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UNIVERSITY OF CALIFORNIA PUBLICATIONS

COLLEGE OF AGRICULTURE

AGRICULTURAL EXPERIMENT STATION

BERKELEY, CALIFORNIA

CALIfORNIA PLANT DISEASES

By RALPH E. SMITH and ELIZABETH H. SMITH

BULLETIN No. 218

(Berkeley, Cal., June, 1911)

SACRAMENTO

W. W. SHANNON - - - - SUPERINTENDENT OF STATE PRTNTING

1911

Benj. Ide Wheeler, Ph.D., LL.D., President of the University.

EXPERIMENT STATION STAFF.

E. J. Wickson, M.A., Director and Horticulturist.

E. W. Hilgard, Ph.D., LL.D., Chemist (Emeritus).

W. A. Setchell, Ph.D., Botanist.

Leroy Anderson, Ph.D., Dairy Industry and Superintendent University Farm Schools.

M. E. Jaffa, M.S., Nutrition Expert, in charge of the Poultry Station.

R. H. Loughridge, Ph.D., Soil Chemist and Physicist (Emeritus).

C. W. Woodworth, M.S., Entomologist.

Ralph E. Smith, B.S., Plant Pathologist and Superintendent of Southern California

Pathological Laboratory and Experiment Station.
G. W. Shaw, M.A., Ph.D., Experimental Agronomist and Agricultural Technologist, in

charge of Cereal Stations.

E. W. Major, B.Agr., Animal Industry, Farm Manager, University Farm, Davis.

F. T. Bioletti, M.S., Viticulturist.

B. A. Etcheverry, B.S., Irrigation Expert.

George E. Colby, M.S., Chemist (Fruits, Waters and Insecticides), in charge of
Chemical Laboratory.

H. J. Quayle, A.B., Assistant Entomologist, Plant Disease Laboratory, Whittier.

W. T. Clarke, B.S., Assistant Horticulturist and Superintendent of University Exten-
sion in Agriculture.

H. M. Hall, Ph.D., Assistant Botanist.

C. M. Haring, D.V.M., Assistant Veterinarian and Bacteriologist.
John S. Burd, B.S., Chemist, in charge of Fertilizer Control.

E. B. Babcock, B.S., Assistant Agricultural Education.
W. B. Herms, M.A., Assistant Entomologist.

J. H. Norton, M.S., Assistant Chemist, in charge of Citrus Experiment Station, River-
side.
W. T. Horne, B.S., Assistant Plant Pathologist.

J. E. Coit, Ph.D., Assistant Pomologist, Plant Disease Laboratory, Whittier.
C. B. Lipman, Ph.D., Soil Chemist and Bacterioligist.
R. E. Mansell, Assistant in Horticulture, in charge of Central Station grounds.

A. J. Gaumnitz, M.S., Assistant in Cereal Investigations, University Farm, Davis.

E. H. Hagemann, Assistant in Dairying, Davis.

B. S. Brown, B.S.A., Assistant in Horticulture, University Farm, Davis.

F. D. Hawk, B.S.A., Assistant in Animal Industry.

J. I. Thompson, B.S., Assistant in Animal Industry, Davis.

R. M. Roberts, B.S.A., University Farm Manager, University Farm, Davis.

J. C. Bridwell, B.S., Assistant Entomologist.

C. H. McCharles, B.S., Assistant in Agricultural Chemical Laboratory.
N. D. Ingham, B.S., Assistant in Sylviculture, Santa Monica.

E. H. Smith, M.S., Assistant Plant Pathologist.
T. F. Hunt, B.S., Assistant Plant Pathologist.

C. O. Smith, M.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier.

F. L. Yeaw, B.S., Assistant Plant Pathologist, Vacaville.
F. E. Johnson, B.L., M.S., Assistant in Soil Laboratory.
Charles Fuchs, Curator Entomological Museum.

P. L. Hibbard, B.S., Assistant Fertilizer Control Laboratory.

L. M. Davis, B.S., Assistant in Dairy Husbandry, University Farm, Davis.

L. Bonnett, I.S., Assistant in Viticulture.

S. S. Rogers, B.S., Assistant Plant Pathologist, Plant Disease Laboratory, Whittier.

B. A. Madson, B.S.A., Assistant in Cereal Laboratory.

Walter E. Packard, M.S., Field Assistant, Imperial Valley Investigations, El Centro.

M. E. Stover, B.S., Assistant in Agricultural Chemical Laboratory.

P. L. McCreary, B.S., Laboratory Assistant in Fertilizer Control.

F. C. H. Flossfeder, Field Assistant in Viticulture, Davis.

E. E. Thomas, B.S., Assistant Chemist, Plant Disease Laboratory, Whittier.

Anna Hamilton, Assistant in Entomology.

Mrs. D. L. Bunnell, Secretary to Director.

W. H. Volck, Field Assistant in Entomology, Watsonville.

E. L. Morris, B.S., Field Assistant in Entomology, San Jose.

J. S. Hunter, Field Assistant in Entomology, San Mateo.

J. C. Roper, Patron University Forestry Station, Chico.

John T. Bearss, Foreman Kearney Park Station, Fresno.

E. C. Miller, Foreman University Forestry Station, Chico.

CALIfORNIA PLANT DISEASES.

By Ralph E. Smith and Elizabeth H. Smith.

An important part of the work of every agricultural experiment
station consists in the dissemination of useful information, as well as
the carrying on of investigations seeking for new knowledge. It is the
former phase of station work which is represented in the present
bulletin. This publication is intended as a handbook of plant diseases
occurring in California, giving a brief description of the nature of the
principal troubles, together with directions for their control. Many
miscellaneous and less important troubles are also described, the plan
being to record all plant diseases of any possible interest which have
been observed in California by members of the department.

The illustrations are all original in this department, save those
illustrating vine diseases reproduced from Bulletin 197 of this experi-
ment station. The photographs have been taken by various members
of the staff, while the drawings are by Miss E. H. Smith.

The meaning of the word ' ' disease, ' ' as it applies in the present sense
tc plant production, is decidedly less specific than the conception of the
same word as applied to the human race or domestic animals. In the
latter case disease may be defined as the opposite of health, and health
means a condition of normal functional activity of the body. In the
growing of cultivated plants or "crops,' however, there are always
two distinct objects or considerations involved for successful, satis-
factory results. These are as follows :

(1) The plant must make a vigorous development and maintain to as
great an extent as possible that condition which we denote as "thrift. "
In almost all cases of crop production it is desirable to maintain thrifty
and vigorous growth. This corresponds quite closely to what we call
"health' ' in the animal body.

(2) Along with this thrifty condition it is likewise necessary to
attain certain arbitrary qualities or characteristics of the root, stem,
leaf, flower, fruit or seed, such characteristics being those which make
the product of the plant most desirable from a commercial standpoint.
Most of these qualities are not at all necessary to a condition of
ordinary health or thrift, and some of them are even opposed to it.

We may, therefore, say in the present sense that we are considering
under the term "disease" any condition of a plant in which there is

.1040 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

a decided failure of thrifty development, or failure of the plant to
produce a commercial product of satisfactory quality or quantity.

This bulletin will impress many, at first sight, as being of a much
more general nature and wider in scope than the usual plant disease
manual. It may seem to some to leave the province of the plant
pathologist and invade that of the soil chemist and physicist, the agron-
omist and the horticulturist. Such a conception of the scope of plant
pathology results from the common impression that all plant diseases
are caused by insects, fungi, bacteria or other living organisms of the
nature known as parasites. This is far from being the case, particu-
larly in a region like California, where the conditions attending the
culture of plants are extremely artificial, the soils largely in a semi-
arid or desert condition before being brought under cultivation, and
where the commercial crops are produced by plants which have been
introduced from all sorts of climates and conditions. Under such
circumstances it is not surprising that soil and climatic conditions
should have powerful influences upon plant growth, and produce
many abnormal effects and disturbances. Such is the case, and in
diagnosing plant troubles in California it is quite as necessary and
usually more difficult to judge such influences accurately than to deter-
mine the work of parasitic organisms. Many of these effects can not
be distinctly segregated or described as specific diseases of certain
plants, but they will be briefly summarized and described in a later
chapter.

The development of plants and the nature of the products which they
bear are influenced by two principal factors : first, the inherent quality
of the plant itself, transmitted through the seed or bud ; second, the
nature of the environment in which the plant develops. One factor is
as important as the other, and the plant pathologist must work through
both in order to attain the desired results. In the former case he enters
the field or calls upon the services of the plant breeder, in order to
obtain varieties of plants having the desired qualities, while in the
latter case he investigates the effects of the various influences and
agencies which act upon the plant during its growth and seeks means
to counteract or stimulate such influences, as the case may be. Here
again the aid of various sciences must be invoked in order to obtain
the desired results. In a recent text-book the matter is well expressed
in the following language: "Every plant has definite requirements for
its best development. The character of the mature plant is the result
of two sets of forces. The first of these is the inherent capacity of the
seed to develop and produce a normal individual of its kind. The
second set of forces constitutes the environment in which the plant
grows, and of which the soil is one part, the other component being

Bulletin 218] CALIFORNIA PLANT DISEASES. 1041

climate. Every plant is an expression of the combination and inter-
action of these three groups of forces — the seed, the climate, and the
soil."*

Ideal conditions for the production of any crop may be summarized
as follows:

In the Plant :

Proper Inherent Qualities of Growth and Production.
In the Air :

Proper Temperature ;

Proper Moisture ;

Proper Light ;

Proper Chemical Composition ;

Freedom from Injurious Influences.

In the Soil :

Proper moisture ;
Proper Aeration ;

Proper Chemical Composition ;

Proper Physical Composition ;

Freedom from Injurious Influences.

In other words, the plant needs in its environment, for successful
development, a proper degree of heat, moisture, air, light, and food, and
freedom from injurious influences. Any serious departure from these
ideal conditions results, in the present sense, in disease.

PLANT PHYSIOLOGY.

A clear understanding of the fundamental principles of normal plant
physiology is necessary to enable one to judge abnormal or diseased
conditions with any degree of accuracy. A brief exposition of this
subject may, therefore, be of use at this point.

Every plant consists of certain parts or organs, each with its parti-
cular duty to perform to maintain the life and activities of the whole.
These parts are commonly as follows : The root, stem, branch, leaf,
flower, fruit and seed. Any or all of these parts is liable to disease,
either in the strict sense of the word, meaning that they may be so
affected as to cause an unhealthy condition, or they may be affected in
the broader sense of having undesirable commercial characteristics,
since all of these parts, in various plants, represent the commercially
desirable portion. Some plants, for instance, like the turnip or carrot,
are cultivated for the root, some for the stem or branches, like the
asparagus or celery, some for the leaf, like the lettuce, and a great many
different kinds for the flowers, fruit, or seed. If the root or stem be
diseased, in a sense of being in an injured or unhealthy condition, the
flowT of water from the ground will be cut off or interfered with and the
remainder of the plant suffer accordingly. If the leaves are injured
or destroyed their functions will be interfered with and the rest of the

* Soils. Lyon and Fippin.

1042

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

plant suffer from starvation. Likewise, the value of the crop will be
injured or destroyed if the particular part of which the plant is
cultivated has imperfections or undesirable characteristics, whether
the health or thrift of the plant is injured or not.

Fig. 1. — Diagram of tree showing movements of fluids as shown by

arrows.

Of the organs mentioned, the root commonly grows in the soil and
the remainder of the plant in the air.

Bulletin 218] CALIFORNIA plant DISEASES. 1043

SOIL RELATION.

The soil has two general purposes in relation to plant growth. In
the first place it furnishes a medium through which the root is able to
accomplish its mechanical function of holding the plant upright in the
air and exposing its parts to the air and sunlight. Second and more
important, the soil is a storehouse of food and moisture, both of which
are indispensable to plant growth. The soil is composed of an aggre-
gation of various sized particles of mineral matter, resulting from
the disintegration of rocks, into which is mixed various amounts of
organic matter, resulting from the decomposition of plant and animal
remains. Being composed of individual particles of irregular shape
there is more or less space between these particles, which is filled either
with water or with air and other gases. The size of the spaces and,
therefore, the amount of water or air which the soil may contain depends
upon the size of the particles and the degree to which they are com-
pacted together.

Far from being an inert mass of dead mineral and organic matter,
the soil is likewise the home of uncounted myriads of living organisms,
not only soil bacteria, of which much has been heard of late, but also
many other forms of low plant life, hosts of simple animal organisms,
and likewise more highly developed creatures, such as earth worms and
many other forms. All of these exert a profound influence upon the
soil and its relation to plant production.

The features of the soil which particularly interest us in this connec-
tion have three phases : chemical, physical and biological. Chemically,
the soil furnishes most of the elements of food which the plant requires,
said elements being derived from the original rocks from which the soil
was formed and the decaying plant and animal remains which it
contains, all being gradually brought into solution in the water which
permeates the soil. The soil may likewise contain substances of a
nature injurious to plants. It is, therefore, most evident that the
student of plant pathology must carefully consider the chemical nature
of the soil in studying the condition and health of the plant.

Physically, the texture of the soil has a very great influence upon the
development of the root, upon the supply of moisture which the soil may
furnish to the plant, upon the availability and accessibility of the food
supply stored up in the soil, upon the performance of cultural opera-
tions necessary to the proper development of the plant and is in every
way fully as important as the chemical consideration.

Biologically, both the chemical and physical condition of the soil are
largely influenced by the activities of the living organisms which it
contains, and this relation is of great importance in many ways to the
growth of the plant. We need not consider these matters in further

1044

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

detail in this place more than to call attention to their fundamental
importance.

The root of the plant spreads through the soil by growth and subdivi-
sion, forming a network of line branches, the extremities of which are
the delicate, minute root hairs through which food and water are
absorbed (Fig. 2). Air is also required by the root as well as by other
parts of the plant. The activities of the root are therefore entirely

dependent upon the physical
texture, moisture supply, tem-
perature and chemical composi-
tion of the soil. If these con-
ditions are favorable, the plant
flourishes so far as the func-
tions of the root are concerned.
If decidedly unfavorable in
any important respect, bad
results or disease follow.

The specific food substances
taken from the soil by the root
are as follows : Nitrogen, hy-
drogen, sulphur, phosphorus,
calcium, potassium, iron, mag-
nesium and oxygen. Some of
these elements may be replaced
to some extent by others, as, for
instance, sodium and calcium
may partly take the place of
potassium and magnesium.
Other non-essential substances
may also be taken up, and in-
deed it may be said that almost
any element in the soil may be
absorbed in considerable quan-
tities. All these elements are
absorbed by the plant through
the root in the form of a solu-
tion in wrater. In other words, the water of the soil is a weak solution
of these and any other soluble substances which the soil may contain.
Each of these substances, with the exceptions stated, is indispensable to
the growth of ordinary plants. In other words, the plant is unable to
develop if any one of these be lacking. Some of them are needed only
in very small amount, and we can scarcely imagine a soil which would
be entirely deficient in any one of these elements. Soils differ, how-

Fig. 2. — Root hairs in soil.

Bulletin 21S]

CALIFORNIA PLANT DISEASES.

1045

ever, in the relative amounts of these substances which they contain
and there is likewise a great difference in the amounts of them which
are demanded by plants. The three elements most likely to be lacking
in quantities sufficient for the maximum development of plants are
nitrogen, phosphorus and potassium. Less commonly calcium (lime)
is lacking, and in some instances an addition of iron to the soil shows a
beneficial effect upon the growth of plants.

A B C D E

Fig. 3. — Section of tree trunk. A outer bark, B inner bark,
C cambium, D sap wood, E heart wood.

The chemical nature of the soil and its modification by the addition
of various substances in the practice of fertilization or soil modification,
form a very complicated subject in regard to its effect upon the growth
of plants. Such effects, while sometimes comparatively simple and
consisting merely in a direct addition to the supply of food material
taken up by the plant, are often extremely indirect, and the ultimate
effect upon the plant may come about through the chemical action of the

1046 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

material upon other chemical substances in the soil, its effect upon living
organisms, or in various other ways. We may cite here, for example,
the recent discussions which have come up in southern California in
regard to the ratio of lime and magnesia contained in soils, the injurious
effects upon plant life of certain combinations of this sort, and the pos-
sibilities of correcting such troubles by the addition of lime or magnesia
to the soil.

From the standpoint of the plant pathologist, the chemical nature
of the soil, through which most of the physical and biological effects are
ultimately expressed, has three main considerations: first, the limiting
of growth by a deficiency in one or more necessary constituents, includ-
ing water; second, a possibility of injurious effects resulting from the
presence in the soil of certain substances in excessive amounts; third,
specific effects of the chemical elements of the soil upon the character
of the commercial product of the plant, such, for instance, as the color,
fiavor or texture of the fruit. In other words, the question arises in
numerous instances as to whether poor growth, lack of fruit production,
deficiency in size, or some other partial failure may be due to a lack or
an excess of some substance in the soil, and also to what extent arbi-
trary characteristics in the commercial product such as color, flavor, or
texture may be influenced by chemical treatment or the chemical nature
of the soil. This, in California, is one of the most important phases of
our subject.

Another feature of the soil, which relates to plant physiology, is its
temperature, a factor which may be of some importance.

MOVEMENTS OF FLUIDS.

After being absorbed by the root the soil solution, or as we may now
call it the sap, passes upward into the plant from the smaller into the
main, larger roots, on up into the trunk. The particular path of this
upward stream is located in the xylem or woody portion of the conduct-
ing fibers; in woody trees of considerable size this upward flow of sap
from the roots is most active in the newer, outer layers of wood or what
we call the ' ' sap wood. ' ' Very large amounts of water, with food mate-
rials in solution, pass up through the stems of plants in this way, as may
readily be seen when we consider the amount of the soil elements which
plants contain, and the fact that the solution in which they come into the
plant from the soil is an extremely dilute one. A large supply of water
is therefore necessary and indispensable to the growth of the plant, not
only for its actual use as food, but also as a conveyor of other elements,
and likewise to maintain the turgidity or rigidity of the whole plant
body. We may say, indeed, that up to a certain point the growth of a
plant is proportionate to the amount of water which it receives, since
the more water the soil contains the more food material will be dissolved

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1047

and given entry to the root. Beyond a certain point the soil may
receive too much water, aeration be too much reduced, and the roots
become sluggish, injured, or even killed. Under the semi-arid condi-
tions of California, however, nothing is so striking in regard to plant
life as the marvelous effect of an abundant water supply upon growth
and fruit production. The crude sap solution passes along up through
the wood or xylem of the stem out into the branches and finally reaches
the leaves.

— S

Fig. 4. — Cross section of leaf, ep upper epidermis,
sm and st sugar and starch-making cells, vb fibro-
vascular bundle, s stoma.

AIR RELATION.

The relation of the plant to the atmosphere which surrounds it is of
supreme importance, its relation being expressed most largely through
the leaves, which act as organs both of absorption and excretion. The
water supply coming from the roots, with its food elements in solution,
comes into the leaves and there the larger portion of the water is
evaporated off into the air by the process called transpiration. This
excess of water passes off in the form of vapor, reaching the air through
minute openings called stomata in the leaf surface. These are usually
more abundant on the lower than on the upper surface of the leaf, and
in the leaves of some plants are confined entirely to the lower portion.

1048 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

At the same time that this process is going on the leaves absorb large
quantities of carbon from the air in the form of carbon dioxide gas.
Carbon completes the list of food substances necessary to the plant,
taken together with those mentioned as being derived from the soil.
The leaves are able, by means of a process exerted through the influence
of sunlight upon their green coloring material or chlorophyll, to
decompose this carbon dioxide and bring the carbon into combination
with hydrogen and oxygen derived from the soil. As a result of this
process, which is called photosynthesis, a succession of chemical changes
occurs which results in the formation of sugar in the leaf, followed by
large quantities of starch. This process goes on during sunlight, and
is indispensable to the life of the plant. During active sunlight in the
daytime a large excess of these substances is formed, so that by evening
the leaf contains an accumulation of starch and sugar. Meantime, both
day and night, the starch is digested into sugar, and a solution of the
latter substance is continually being distributed from the leaves to all
parts of the plant where growth is taking place or where food material
is being stored up. This current passes largely through vessels called
the sieve tubes, which in woody plants are located in the inner bark.

Before the materials formed by photosynthesis can be assimilated by
living substance, they are formed into new compounds containing
nitrogen. A variety of complicated chemical processes goes on all over
the plant in which use is made of the various materials taken from the
soil, and the various substances formed build up the growth of new
parts, the formation of fruit, or are otherwise made use of in the
activities of the plant.

Respiration goes on in the leaves in a manner chemically similar to
that in animals. Oxygen is taken in and carbon dioxide given off.

RELATION OF THE PLANT TO CLIMATIC CONDITIONS.

The atmosphere has many relations to the growth of plants other
than that of supplying carbon dioxide and oxygen to the leaves. Its
temperature, for instance, is one of the most important factors in con-
trolling the distribution of plants or the choice of location where certain
species can be grown. The humidity of the air, its degree of moisture or
dryness, is also of considerable importance. The degree of light which
the leaves receive is a very important matter, especially as it influences
the process of photosynthesis, which is the first, fundamental operation
in the nutrition of the plant. The air may also contain substances
injurious to vegetation, although this rarely, if ever, occurs naturally.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1049

CAUSES OF PLANT DISEASE.

Non-Parasitic Troubles.
Atmospheric :

Excessive Cold ;

Excessive Heat ;

Excessive Dryness ;

Excessive Moisture ;

Wind ;

Hail;

Artificial Influences.
Soil:

Deficiency of Necessary Substances ;

Excess of Certain Substances (Alkali, Salt, Acid) ;

Excessive Dryness ;

Excessive Moisture ;

Faulty Physical Structure (Hard-pan, Heavy or Coarse subsoil) ;

Artificial Influences.
Parasitic Troubles.

Higher Animals (Gophers, Moles, Squirrels) ;

Insects ;

Worms ;

Mollusks (Slugs, Snails) ;

Higher Plants (Dodder, Mistletoe) ;

Fungi ;

Bacteria ;

Slime Moulds.

The above table indicates most of the influences which affect plants
injuriously in California, so far as they can be definitely tabulated. It
should be further mentioned that, in many cases, various combinations
of the above have disastrous results which could not be attributed to any
influence acting alone.

DIRECTIONS FOR EXAMINATION OF DISEASED PLANTS.

Before proceeding to a description of the principal troubles of our
various crops it may be useful to give the following general directions
for the examination of unhealthy plants :

1. Note whether any particular portion of the orchard or field shows
the trouble worse or less and, if so, seek to find wherein conditions are
different there from those in the remainder of the planting.

2. Note whether any particular kind or variety of the crop is more or
less affected than others, also whether any particular individuals show
marked resistance, immunity or freedom from the trouble. Ascertain
the commercial qualities and desirability of any seemingly resistant or
immune variety or individuals.

3. Determine as accurately as possible the part of the plant which is
actually affected. In many cases, for instance, the leaves or top may
wilt and die when the real trouble is in the roots.

4. Look first for the simplest effects, such as those of animals, frost or
other climatic influences, simple injuries or other obvious causes of
trouble.

1050 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

5. Look for indications of alkali, salt, poor drainage, too light or too
heavy soil or other injurious soil conditions, as shown by surface incrus-
tations, the occurrence of native vegetation peculiar to certain conditions
or any peculiarity in the appearance of the soil in the region of the
affected plants.

6. Look for the presence of fungi, insects or other parasites, so far as
one's ability extends in this direction. Endeavor to observe accurately
and judge intelligently whether the organisms found are the cause of
the trouble or simply secondary.

7. If nothing is found above ground to indicate the cause of the
trouble, dig or bore a hole to the depth reached by the lowest roots.
During the digging notice the condition of the roots, the consistency of
the layers of soil, the amount of moisture which they contain, and their
relation to the development of the roots. Look carefully for any
peculiar or suspicious condition, either in the roots or soil, and continue
the examination out to the smallest roots and down to an ample depth.

8. Ascertain as closely as possible all that can be found out about the
previous history and treatment of the soil and plants, all information
of possible value as to irrigation practice, fertilization, cultural methods
and previous climatic conditions ; also the nature of the trouble from its
very first appearance.

9. If necessary, examine healthy groves, trees or plants of the same
kind, making the same examinations and inquiries, and endeavor to
ascertain wherein conditions differ from those where the trees or plants
are diseased.

After this examination, if more information is desired, endeavor to
select the most characteristic samples, either of parts of the plant or
soil, and send them to the proper authority with complete information
as to the nature and occurrence of the trouble. In sending parts of
plants, pack them so that they will remain as fresh as possible. In
obtaining soil samples take a fair sample from each foot down to a depth
of four feet.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1051

SOME OF THE MOST COMMON EEEECTS OE INJURIOUS ATMOSPHERIC
AND SOIL CONDITIONS IN CALIFORNIA.

ATMOSPHERIC INFLUENCES.

Frost and Cold. — The effects of low temperature, in most of the culti-
vated portions of California, are only such as are produced by infre-
quent frosts or injurious effects of temperatures very little below the
freezing point and lasting usually but a few hours. Such effects are in
most cases evident and unmistakable, needing no detailed description
and resulting simply in the death of the parts or organs which are
severely frozen. This is seen, for instance, in the not infrequent killing
of fruit blossoms and young shoots by late spring frosts, the nipping
back of young and tender growth of citrus trees during occasional cold
nights in the winter, and other similar effects. In regard to such
injuries, the grower was formerly at the mercy of the elements, depend-
ing for protection only upon choice of location in planting and avoiding
places known to be dangerous for a certain crop on account of likelihood
to frost. In comparatively recent times, however, appliances and meth-
ods of frost protection have received much attention, and a high degree
of satisfaction has been obtained. By the development of such methods,
the culture of some of our more tender plants has been extended into
regions hitherto dangerous.

One of the most difficult frost injuries to detect is the slight freezing
of oranges, which occurs now and then in some sections. When this
happens the internal texture of the fruit is injured, its juice partially
disappears, and a greater or less portion of the pulp of the orange
becomes dry and insipid. Fruit which is badly affected in this way
may be readily detected in handling by the experienced sorter, but occa-
sionally there may be a considerable quantity of slightly affected fruit
which is extremely difficult of detection until the oranges reach the con-
sumer. A specific gravity method has been employed to some extent,
eliminating all the oranges which float in a liquid of a certain density.
This method works somewhat to the disadvantage of the producer, taking
out all the lighter oranges, whether frozen or not.

Another somewhat obscure effect of freezing is seen occasionally in
young citrus and other trees in a killing of the inner bark just above the
surface of the ground. Not infrequently young trees, which appear to
have gone through the winter without harm, as indicated by the appear-
ance of the top, begin to fail and die later in the spring, and on exam-
ination it is found that the inner bark and wood in the vicinity of the
cambium layer are entirely dead for some distance just above ground.

In the case of deciduous fruits (see Almond, Apricot, Cherry, Peach
and Pear), severe frost just after the fruit has set sometimes kills the

1052 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

young germ of the seed without causing the fruit to drop or even check-
ing its growth for some time. Such fruit sometimes reaches considerable
size before falling and is then found to contain a black, shriveled seed
germ, killed by frost.

In citrus districts most subject to low temperatures during the winter,
with occasional severe freezes, there sometimes seems to occur a general
lowering of the vitality of the trees, and an appearance of weak, un-
healthy, mottled-leaf condition. In such regions where a considerable
portion of the young growth of the trees is frequently killed back, a
condition of degeneration lasting all through the season may occur,
particularly if the trees do not receive the best cultural treatment.

The matter of frost injury in most parts of California, where the
injurious degree of temperature is very slight, its duration short, and
its occurrence comparatively rare, is very much affected by compara-
tively slight influences, particularly the condition of growth in the plant
and the degree of moisture in the soil. By so handling the crop as to
keep down as much as possible the production of tender new growth
during the cold season, by keeping the soil in moist condition, and by the
use of the comparatively simple protective means about to be described,
much of the frost damage which is likely to happen in California may
be prevented.

Frost prevention, both for citrus and other crops, has received much
attention in recent years, and with a large measure of success. For pre-
venting damage to tender growth, fruit or blossoms on cold nights,
methods have been perfected which consist in burning smoky, sooty
fuel, such as soft coal or low grade oils, in numerous small receptacles
placed upon the ground at proper intervals whenever the temperature
approaches the danger mark. A variety of patented devices for this
purpose is upon the market, and literature upon the same may be
obtained from the makers.

In the case of young trees, particularly citrus, special attention is
required to carry them through the first three or four years in localities
subject to occasional frosts. The damage described above, where the tree
is killed just at the surface of the ground, and likewise the killing back
of the top is successfully prevented by banking up the earth somewhat
about the trunk in the fall, and by the use of a wrapping or protector of
some sort about the trunk. A common practice with citrus trees consists
in tying several cornstalks, palm leaves, tule or similar material about
the trunk of sufficient length to enclose and protect most of the top of
the tree at the same time. In many places citrus groves have been
successfully developed by thus protecting the trees during their first
two or three years in the orchard, when without such protection it would
have been almost out of the question to get a growth started.

Bulletin 218] CALIFORNIA plant DISEASES. 1053

Heat. — Cultivated plants in some portions of California are subjected
to very extreme degrees of heat during the summer time, and the choice
of crops for certain localities is largely influenced by this factor. Be-
yond this, injury from unusual degrees of heat, particularly when com-
bined with extreme atmospheric dryness, is of quite frequent occurrence.
The effect of this is usually seen in a sudden burning and withering of
the leaves, producing an effect sometimes called sun-scald. Much
damage is sometimes caused in the same manner to fruit, particularly
grapes, and occasionally some of the deciduous fruits. This injury
shows itself as a burning or withering of the fruit on the exposed side,
or a shriveling and drying of the fruit before it reaches full size. This
trouble is frequently seen in prunes in the northern part of the State.
Trouble of the same sort is also common with the English walnut. Quite
frequently an unusually hot, dry period, particularly when the crop is
approaching maturity, causes a withering and blackening of the exposed
sides of the green hulls which enclose the nuts, and this burning extends
as a discoloration into the meat of the nut itself, causing the hull to stick
to the nut on that side, and the nut to blacken, both inside and out. This
form of sunburn often causes large losses to the walnut grower, and
also limits the growth of this crop to regions where the sun is not too
severe.'

The condition of weather, commonly known in this State as a "hot
norther " or " Santa Ana, ' ' is frequently the cause of much damage to
some crops, especially when occurring early in the season. The condi-
tion referred to consists in a hot, extremely dry, electrical wind, blowing
from the interior or desert portions of the State toward the coast.
When such winds occur the blossoms of fruit trees are sometimes killed
and young sprouts dried up and destroyed, the latter particularly in the
case of buds or grafts which have recently been put in. The English
walnut is also particularly susceptible to this form of injury when in
bloom. The damage in this case appears to be done mainly to the pollen,
and if this sort of weather occurs just when the catkins are shedding
their pollen, the setting of the crop may be very seriously affected.

Another condition commonly called sunburn is of frequent occurrence,
affecting the stems or trunks of young trees. This is almost invariably
seen on the southwest side 'Of the tree, although local peculiarities may
influence this feature somewhat. The trouble is due to a killing of the
cambium layer by the heat of the sun and results in an area of dead
bark extending up and down the trunk or on the sides of larger limbs,
through which decay often sets in and the tree is badly injured or killed.
This form of sunburn is seen particularly in young trees recently set out,
where the trunks are exposed to hot sun before the trees have been able
to draw a plentiful supply of moisture from the soil by the formation

2— Bul. 218

1054 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

of new roots. Trees which for any reason make a poor start and fail
to root properly are especially liable to sunburn in the trunk. When,
for example, nursery trees are allowed to become too dry before planting
this frequently occurs and the trees may be entirely killed, damaged on
one side or, in some cases, may throw out new shoots from the lower
portion of the trunk.

This occurrence of sunburn is by no means confined to the summer
season, but takes place even more commonly during the winter in our
climate. Particularly with such trees as the walnut, apple, peach and
prune, which shed their leaves in the winter, the sap movement does not
become entirely dormant during the winter but is kept in a state of irreg-
ular activity by the occurrence of frequent periods of warm weather.
Especially in regions where the nights are fairly cold and the days hot
during a considerable portion of the winter, trees of this sort become
badly sunburned. The sap starts and stops again in the trunk and
without the presence of leaves to regulate this flow in a normal manner
abnormal conditions occur in the cambium and the hot afternoon sun
causes a burning of one side of the trunk. Toadstool or other fungi
causing decay may then effect an entrance through such a wound and
the tree is destroyed. Sunburn is prevented by the presence of an
abundant supply of moisture in the soil more than by any other in-
fluence. We may, of course, except from this statement the influence
of shade, or climatic conditions not conducive to damage of this sort.
Other things being equal, however, trees or plants having an abundant
supply of moisture in the ground are much less likely to suffer from
sunburn, either in the trunk or as affecting the fruit. It is therefore
advisable to give plants and trees a particularly abundant supply of
water in hot, dry times when the fruit may be kept from injury by
this means, and also during the fall and winter, if abundant rains do
not occur, in order to prevent damage to the trunks and buds. In the
case of nursery trees which have become too dry before planting, it is
often advisable to cut them back nearly to the ground and allow a new
shoot to come up and form the trunk. This should always be done
when the tree is found to be badly sunburned and standing in a dormant
condition without throwing out any new growth. By thus bringing up
a fresh shoot from below, through which the sap is able to circulate
freely, a good, thrifty tree is often produced, while if the tree is not cut
back it stands all through the season throwing out a few stunted, sickly
shoots from its sunburned trunk and very likely dies entirely.

In the case mentioned of deciduous trees which become sunburned
in the trunk during the winter time on account of an irregular activity
of the sap, this condition is usually aggravated if the surface of the soil
is bare and free from vegetation. Frequently the same influences which
cause sunburn prevent the development of vegetation on such soils, on

Bulletin 218] CALIFORNIA PLANT DISEASES. 1055

account of the extreme variation in temperature in winter between the
day and the night. Heavy frosts occur at night, freezing the surface
of the ground, while the hot sun of the day heaves it up and destroys
any seedlings which may have started. The only thing which can be
done in such a case is to make every effort to get some sort of growth
started during the fall before the coldest nights come on. This is fre-
quently difficult on account of a lack of water for starting such a growth.
If it is not feasible the next best thing is to mulch the surface of the
ground about the trees, covering it with straw or any similar material
which may be available. It is also advisable to cover the trunks and
main limbs of any trees which are in danger of sunburn with a coating
of thick whitewash. This should also be done to prevent sunburn wThen
the tops of trees are heavily cut back for any purpose, as. for instance,
after top-working them to other varieties.

Before leaving the subject of the relation of temperature to vegeta-
tion in California, we may say that many peculiar and obscure effects
frequently occur as a result of bringing plants native to the temperate
zone and accustomed to a definite period of dormancy during the winter,
to a region where the change of the seasons is so slightly marked. These
plants are by nature accustomed to and prepared for a dormant period
during a portion of the year. They not only drop their leaves and
cease their growth at the approach of winter, but also undergo chemical
and various other physiological changes in preparation for this dormant
period. The stimulation or irritation caused by the frequent occurrence
during the winter of weather conditions entirely similar to those normal
to the spring time, must cause a frequent starting and stopping again of
those processes which go on in the tree during the normal commencement
of growth in the spring, and in this way pathological conditions are
produced. To conditions of this sort appear to be partially due such
troubles as little leaf of the peach, walnut yellows, sour sap of stone
fruits and possibly other of the so-called physiological or climatic
diseases. The only relief to be expected from this trouble is through the
planting of species or varieties of fruit which are known to be unaffected
by such disturbances.

Excessive Dryness. — This subject has already been treated in connec-
tion with extremes of temperature. High temperature in California is
almost invariably accompanied by extreme dryness and the two work
together in producing burning of foliage, withering of fruit and similar
effects.

Excessive Moisture. — Little trouble of this sort is experienced in Cali-
fornia, since no rain falls during most of the growing season of the
majority of our crops. Fruit setting is sometimes prevented by violent
or long continued rains during the blossoming period, this result being

1056 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

produced largely by interference with or prevention of the process
of pollination. Most of our deciduous fruits have the unfortunate
habit of blooming just when our most abundant rains are likely to occur
and the setting of fruit is sometimes considerably diminished by this
means. In many cases also imperfect pollination results and the fruit
either falls after growing for a short time or the seed does not properly
fill.

Our most serious effect of excessive moisture in the air is probably
that of favoring the development of various fungus diseases and causing
thus an indirect injury. It is an almost universal rule that the develop-
ment of parasitic fungi is favored by atmospheric moisture and very
marked differences result in California in the occurrence of plant
diseases in various seasons according to the amount of moisture which
occurs. The same comparative effect is seen in different sections of the
State, the same crop being badly affected by a fungus disease in one
place and entirely free from it in another, as a result of a difference in
atmospheric moisture conditions.

Wind. — This is an important consideration in connection with Cali-
fornia agriculture, particularly in the case of the production of tree
fruits. In choosing a location for an orchard, and particularly a citrus
grove, this feature should be considered along with temperature, char-
acter of the soil and water supply. The bad effects of wind are mostly
mechanical, consisting in a bruising of the fruit by contact with the
branches and twigs. More than this, serious loss is often caused in
windy localities by quantities of fruit being actually blown from the
trees on to the ground before it is ready for picking. In very windy
localities the growth and form of the trees are decidedly affected, the
tendency usually being to cause the tree to lean over and make its prin-
cipal growth in the direction of the prevailing wind. In a few cases,
notably the apricot tree, it is a curious fact that the tree shows the
opposite response, its branches curving over and pointing directly into
the face of the wind. In very windy localities, particularly along the
coast, the young shoots in the tops of the trees are continually killed
back by the wind, which, together with the breaking off of large limbs,
gives the trees a stunted and deformed appearance. Citrus fruit from
windy localities loses much in quality on account of being covered with
scars and blemishes, and also in quantity, as just stated, on account of
being blown from the trees.

On the other hand, a locality otherwise desirable for orcharding
should not be too hastily condemned on account of wind. Most parts
of California are comparatively windy in their primitive state on
account of the absence of trees to break the force of the wind. It is very
noticeable that as a given locality or valley becomes settled, and the

Bulletin 218] CALIFORNIA PLANT DISEASES. 1057

country is broken up with buildings and trees, the wind currents become
less severe and less damage results from this cause than at first. In
almost all orchard planting in new districts this fact is taken into
account, and protection from the wind is attempted and attained to a
more or less extent by the planting of rows of trees called wind-breaks.
This is done by planting close rows of suitable trees at intervals across
the path of the prevailing wind, on the windward side of orchards, or
home sites, or in any position which will best break the wind in the
locality where protection is desired.

For this purpose eucalyptus trees have been most commonly used
in California, particularly the blue gum? Eucalyptus globulus, in all
regions adapted to its growth. It is customary to plant these trees
about eight feet apart, using two or three rows in an alternate manner.
Another tree much used for wind-breaks is the Monterey cypress. This
makes a much denser growth close to the ground than eucalyptus, and
needs to be planted only in a single row. Its growth is slower than
that of the blue gum but rapid compared with that of most trees other
than eucalyptus. Often a combination is made of cypress and eucalyp-
tus planted alternately in a single row. This makes a taller and more
rapid growing break than cypress alone and a denser one than eucalyptus
alone.

Wind-breaks have a serious objection on account of the large amount
of moisture and plant food which these large, rapid-growing trees take
up. With eucalyptus, particularly, it is impossible to grow thrifty
fruit trees within a space of fifty or more feet of the wind-break after
the trees become large. The shade of the trees also has a detrimental
effect upon the neighboring fruit trees, and a still further objection is
the formation of so-called frost pockets, the latter being due to a lack of
air circulation on cold nights in the portions of the grove most sheltered
by the wind-break. The grower must decide for himself in individual
cases whether the benefit of such a planting will more than repay its
disadvantages. There is a marked tendency at present in our older
settled districts to cut down the original wind-breaks, since the general
development of the country has broken up the sweep of the wind and the
land occupied by these eucalyptus or other trees is now more valuable for
fruit trees or other purposes.

Hail. — Violent hail storms are of occasional occurrence, even in the
most frost-free portions of California. Damage is sometimes caused
through the bruising of fruit and the breaking of foliage and twigs.

Artificial Substances in the Air. — We have already said that the atmos-
phere never contains normally anything injurious to plants. Fre-
quently, however, in the vicinity of cities or industrial enterprises,
various emanations are poured into the air and act disastrously upon

1058 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

vegetation. Such effects are frequently seen in the vicinity of smelters,
chemical works, or in localities where soft coal containing large amounts
of sulphur is burned. Particularly injurious are the fumes resulting
from the burning of sulphur in any form, if they come into contact
with vegetation without being very much diluted with air.

The subject of smelter fume injuries has received very extensive
investigation both in this country and Europe for many years. This has
also been the subject of a vast amount of expensive litigation between
smelting and other companies on the one hand, and agricultural or
timber interests on the other. There is no subject which needs the most
competent expert attention and the most careful judicial consideration
more than this. Grave and extensive injustice may be done by an
improper finding for either the smelting or the agricultural interests.
Both industries are of great importance, and their relative rights and
standing must be carefully considered in cases where their interests
seem to clash. From the standpoint of the smelting company, there
should be clearly and positively established the amount of damage which
is actually being caused by the fumes and the relative value of the agri-
cultural interests affected in proportion to that of the smelting and
mining interests. There is invariably a very natural tendency in the
vicinity of smelting and similar plants to lay to the smoke all sorts of
plant and animal troubles, real and imaginary, which are not caused
by any other very obvious agency. In all agricultural pursuits there
is a certain element of uncertainty, due to climate, soil conditions, and
other uncontrollable and obscure factors. In normal districts a certain
amount of animal and plant disease, crop failure and similar conditions
is expected from such sources. Given, however, a specific, ever-present
agency, known to be injurious under certain conditions, and it is a
natural tendency to lay all sorts of troubles which can not be otherwise
accounted for to this one cause. On the other hand, it is sometimes the
tendency of the smelting company, partly perhaps in self-protection, to
attempt to lay all troubles and injuries to effects other than smoke, and
minimize as much as possible the damage which is actually caused.

There can be but one satisfactory basis of settlement of all such cases,
namely, as we have already said, a careful, expert, and unprejudiced
examination of actual conditions and a settlement of damages or deter-
mination of future policy on this basis. In many European districts
permanent courts or arbitration boards have been established under state
control to settle these questions and this method is far superior to a
constant wrangling in the courts with final decisions based on the relative
arguing ability of the opposing attorneys or the influence of more or
less incompetent, so-called experts, subsidized by the opposing sides to
present their cases in the best possible light. If this matter is properly

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1059

managed, there is no reason why agriculture and mining should not both
be carried on to mutual advantage and without antagonism.

The specific effects of smelter fumes upon vegetation can not be stated
or described in such a manner as to make their identification absolutely
certain. In a general way it may be said that such effects consist in a
spotting or burning of the leaves, and we may also say that there can be
no injury without such spotting or burning. In other words, there is
no such thing as an invisible damage to plants by smelter fumes. Leaf
spot, however, is caused by so many other agencies and conditions that

Fig. 5. — Effect of smelter fumes on leaves of alfalfa.

only the most careful local examination, and broad, general knowledge
of other effects which act injuriously upon vegetation, can enable one
to positively distinguish smoke injury. Microscopic study of injured
tissues is of much assistance to the experienced investigator, but here
again no definite symptoms can be laid down which distinguish this
injury from all others. Chemical analysis, also, has its place, but does
not suffice to distinguish arbitrarily and specifically all smelter smoke

1060 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

injury from every other possible source of trouble. One having a gen-
eral knowledge of plant pathology and entomology can usually soon
eliminate in a smoke district many fungus, bacterial and insect effects
which have been ascribed more or less to the smoke, but beyond this he
may encounter effects of frost, unfavorable soil or climatic conditions,
lack of proper cultivation, effects of fire and many other influences
which must be thoroughly understood and considered. On the other
hand, he must not exaggerate such effects as these and attribute to them
injuries which are really due to the smoke.

Different species of plants vary widely in their susceptibility to smoke
injury, and the amount of injury is also decidedly influenced by weather
conditions. Other things being equal, more damage to vegetation is
caused during wet than in dry weather. This may be due to the fact
that the injurious substances are absorbed by moisture, and thus brought
into contact with vegetation in a more concentrated form when it is wet.
More injury is caused in localities where the wind tends to blow steadily
in one direction much of the time than in places where the currents of
air are constantly shifting. In the latter case, a fairly concentrated
smoke may cause no appreciable damage, while, in the former, quite
dilute fumes may mark out a very evident path of destruction on the
vegetation in the direction of the prevailing wind.

Damage is also sometimes caused by manufacturing plants which
discharge large amounts of dust into the atmosphere. This is the case
in the manufacture of cement, where great quantities of dust go out
into the air and settle upon the leaves of surrounding vegetation, the
dust often setting like cement to a considerable extent. This is very
destructive to the appearance and selling quality of fruit or vegeta-
bles upon which it occurs, and in the case of trees, particularly ever-
greens like the orange and lemon, there appears to be in some cases
considerable damage to the vitality of the tree. This may come about
through an interference with photosynthesis, caused by the light being
cut off through the layer of dust upon the leaves and resulting in injury
to the nutrition of the tree, although this fact has not been clearly
established. There is nothing in the dust itself which would be chem-
ically injurious to the tree or soil. Question has also been raised as to the
effect of such dust deposition upon pollination and the setting of fruit.
"With citrus fruit it is well to bear in mind that damage of this sort is
very doubtful in many cases, since in our most popular variety of orange,
the Washington Navel, and to some extent in other citrus fruits, pollina-
tion is not necessary, and does not ordinarily occur, the fruit developing
by vegetative growth. The same condition exists to a greater or less
extent in other citrus fruits which have a tendency toward seedlessness.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1061

SOIL INFLUENCES.

Deficiencies. — We have shown before that the plant requires from the
soil certain specific chemical elements in proper amounts and propor-
tions, together with a large amount of water. The plant differs from
the animal body in that it may continue growing in size throughout its
Avhole life rather than ceasing to increase at a certain stage of maturity.
The amount or rapidity of this increase, if temperature conditions are
favorable and no injurious influences present, depends almost entirely
upon the amount of the necessary elements and the supply of water
which is available in the soil. Particularly noteworthy in this connec-
tion is the fact that the lack of one element may keep back the whole
development of the plant, even though all the others are present and
abundant. On this account the whole matter of successful soil fertiliza-
tion depends almost entirely upon the determination of the limiting
element or elements and applying these in sufficient quantities for maxi-
mum results, without at the same time using quantities or elements
which are wasteful and without effect.

In this connection the function of water and the possibility of its
being the limiting factor, rather than any chemical element, can not be
too strongly emphasized. There is no question that in a large portion
of the citrus acreage of California, for instance, where artificial fertil-
izers are applied more or less regularly and in fairly large amounts, the
deficiency of water is greater than that of any chemical element and a
large portion of the fertilizers applied remains inert in the soil or is
washed away by rain without ever reaching the interior of the tree.*
For this reason it is extremely important in the examination of unthrifty
trees to inquire carefully into the irrigation treatment which the trees
have received, and? much more important, to examine the soil to a depth
of several feet and find out positively the moisture condition of the lower
layers of soil. This is discussed more particularly in a later paragraph.

We would not infer by this that soils are never deficient in chemical
elements, or that fertilization is never effective. Many soils are decid-
edly deficient in one or more of the essential elements, and practically all

* In order to give further weight to this point we append the following quotation :
"From a theoretical point of view it is not possible to say that any one of the
main soil constituents is more important than any other, since all are necessary to a
proper functioning. Practically, however, there can be no two opinions as to the
supreme importance of the soil water. Nine times out of ten it is the supply of this
constituent which limits crop production. Usually the other constituents are suffi-
ciently if not maximally, favorable, and poor water supply and infertility go hand
in hand. Controlled water usually means controlled fertility. The soil water must
occupy, then, a very prominent place in the theories of the soil physicist, and the
study of its nature and movements must ever be a most important and absorbing
branch of his activity. Nor is the importance of the soil water intrinsic only. It is
the medium of the soil solution and only through it are the necessary food elements
carried from soil to plant. From soil chemist, as from soil physicist, the soil water
is receiving ever increased attention and especially so in the light of the most modern
theories of the dynamics of plant food." — E. E. Price, "Studies in Soil Physics II"
The Plant World, Vol. U, page 59.

1062 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

soils, after continuous cultivation for several years, become exhausted.
Moreover, there are many cases of soils where thrifty plants and profit-
able crops can still be grown without fertilization, and yet, by such
practice, an increased crop can be obtained which will prove a profitable
investment on the cost of fertilization.

The effects of a deficiency of any of the elements most commonly lack-
ing in soils, nitrogen, phosphoric acid or potash, are seen as a backward-
ness in the development of the plant. Nitrogen is most noticeable in its
effect upon growth, and is most likely to be lacking in California soils,
yet an actual deficiency of any of the other necessary elements is equally
effective in checking development. The specific effects of the various
elements upon plant life are frequently described, but we have little
definite information of this sort as applied to California crops. With
the orange, for instance, we are frequently told that nitrogen promotes
especially the growth of the tree; that phosphorus is most concerned
in the setting of the fruit, and that the application of potash produces
more sugar in the fruit. Various statements are also frequently made
as to the effect of these various elements upon the fruit in its time
of maturity, its flavor, texture, color, and various other characteristics.
"We are also told that lack of iron has a marked influence in causing
yellow, light-colored foliage, and that an application of this element
will remedy such a condition. In regard to these ideas, however, we
may say that certainly most of them have never been definitely proven
in California. The most careful experiments have almost entirely
failed to show any specific effects or differences of this sort. So many
other influences come in, such as those of temperature and other cli-
matic conditions, soil moisture, variation in trees and other compli-
cated factors, that it is very easy to ascribe marked differences, noticeable
in a single season, to some substance which has been applied to the soil,
when really some other influence altogether was responsible for the effect
observed. The best evidence goes to show that any fertilizing element
or any other influence which promotes the growth of the citrus tree like-
wise promotes and increases the production of fruit. It also appears
to be a fact that citrus trees which are best nourished and in the most
thrifty condition bear the best fruit, and are in every way most profit-
able.

The specific subject of the methods and materials of soil fertilization
is too extensive a one for complete consideration here. Persons desiring
information along this line should consult some of the numerous pub-
lications upon the subject.

We may say, in brief, that the substances mentioned as being most
likely to be needed, nitrogen, phosphorus, and potash, are commonly
supplied either in the form of stable manure or in various substances,
the preparation of which forms a large and important industry. Nitro-

Bulletin 218] CALIFORNIA PLANT DISEASES. 1063

gen is supplied in the form of salts, such as nitrate of soda and sulphate
of ammonia, or in various substances prepared from slaughterhouse
refuse, such as bone, dried blood, and tankage. Phosphorus comes com-
monly either from finely ground mineral phosphates, which are usually
treated with sulphuric acid to make them more soluble and are then
called superphosphate, or in the form of bone or other animal refuse.
Potash, as used in California, comes almost exclusively from the salt
sulphate of potash, which is mined in Germany. The various fertilizer
dealers supply these different materials and are also in the habit of mix-
ing them together in supposedly proper proportions into so-called com-
plete fertilizers, which are easier and, for the inexperienced, sometimes
safer to use.

Deficiencies in nitrogen in the soil are also supplied in many cases
very satisfactorily and economically by growing and plowing under
so-called green manure or cover crops. For this purpose are used
certain plants, such as clover, vetch, peas or other legumes, which have
the power of absorbing nitrogen from the air. By adding large amounts
of such material to the soil its stock of nitrogen is appreciably increased
and its mechanical condition likewise improved.

Excesses. — Plant troubles due to an excess of certain substances in the
soil are very frequently met with in California. This is particularly
the case in so-called alkali soils. In such cases the soil is impregnated
with excessive and harmful amounts of certain salts which in more
humid climates are dissolved by the frequent rains and carried away
in the drainage.

Alkali Soils. — The most common of the alkali salts are the so-called
white alkali, sodium sulphate, and black alkali, sodium carbonate.
Another substance frequently found in soils in injurious amounts is
common salt, sodium chloride. The presence of these salts is not usually
difficult of detection in a superficial examination, while by chemical
analysis their presence and amount can be absolutely determined.
Alkali lands are usually characterized by spots or areas of greater or
less extent where a white incrustation can be seen upon the surface of
the ground. Black alkali is so called from the fact that when wet
it dissolves the humus of the soil, forming a black, greasy looking sub-
stance upon the surface of the soil, or giving a black color to surface
water. The effect upon native vegetation is always quite characteristic
of the presence and amount of alkali salts. Certain species of plants
prefer alkali soil and flourish according to the amount of these sub-
stances which the soil contains. Most plants, however, are easily
injured by them, with the result that spots containing any considerable
amount of these injurious salts either have upon them the above men-
tioned characteristic plants or remain bare of vegetation with the alkali

1064 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

crust upon the surface, while the surrounding ground is covered with
normal vegetation. In every case where there is any reason to suspect
the effects of alkali or other injurious salts, the soil should be chemically
analyzed down to a depth of several feet.

The present subject, although belonging more in the field of the soil
chemist than that of the plant pathologist, is of so much importance in
the study of plant diseases in California that we have thought it desir-
able in this chapter to make the following quotations from Professor
E. W. Hilgard's authoritative treatment of the subject:*

Effects of Alkali Upon Culture Plants. — In land very strongly impregnated with
alkali salts, most culture plants, if their seed germinates at all, will show a sickly
growth for a short time, "spindle up" and then die without fruiting. In soils less
heavily charged the plants may simply become dwarfed, and fruit scantily. The
effect on grown trees around which alkali has come up, is first, scanty leafage and
short growth of shoots, themselves but sparsely clothed with leaves.

Nature of the Injury to Plants from Alkali. — When we examine plants that have
been injured by alkali, we will mostly find that the visible damage has been done
near the base of the trunk, or root crown; rarely at any considerable depth in the
soil itself. In the case of green herbaceous stems, the bark is found to have been
turned to a brownish tinge for half an inch or more, so as to be soft and easily peeled
off. In the case of trees, the rough bark is found to be of a dark, almost blackr
tint, and the green layer underneath has, as in the case of herbaceous stems, been
turned brown to a greater or less extent. In either case the plant has been practi-
cally "girdled," the effect being aggravated by the diseased sap poisoning more or
less the whole stem and roots. The plant may not die, but it will be quite certain to
become unprofitable to the grower.

It is mainly in the case of land very heavily charged with common salt, as in the
marshes bordering the sea, or salt lakes, that injury arises from the direct effects
of the salty soil-water upon the feeding roots themselves. In a few cases the
gradual rise of salt water from below, in consequence of defective drainage, has
seriously injured, and even destroyed, old orange orchards. The natural occupancy
of the ground by certain native plants may be held to indicate that the soil is too
heavily charged with saline ingredients to permit healthy root growth or nutrition
until the excess of salts is removed.

The fact that in cultivated land the injury is usually found to occur near the
surface of the soil, concurrently with the well-known fact that the maximum accu-
mulation of salts at the surface is always found near the end of the dry season,
indicates clearly that this accumulation is due to evaporation at the surface. The
latter is often found covered with a crust consisting of earth cemented by the crystal-
lized salts and later in the season with a layer of whitish dust resulting from the
drying-out of the crust first formed. It is this dust which becomes so annoying to
the inhabitants and travelers in alkali regions, when high winds prevail, irritating
the eyes and nostrils and parching the lips.

Effects of Irrigation. — One of the most annoying and discouraging features of the
cultivation of lands in alkali regions is that, although in their natural condition
they may show but little alkali on their surface, and that mostly in limited spots,
these spots are found to enlarge rapidly as irrigation is practiced. Yet since alkali
salts are the symptoms and result of insufficient rainfall, irrigation is a necessary
condition of agriculture wherever they prevail. Under irrigation, neighboring spots
will oftentimes merge together into one large one, and at times the entire area, once
highly productive and perhaps covered with valuable plantations of trees or vines,
will become incapable of supporting useful growth. This annoying phenomenon is

*"Soils," pages 426-429.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1065

popularly known as "the rise of the alkali" in the western United States, but is
equally well known in India and other irrigation regions.

The soil being impregnated with a solution of the alkali salts, and acting like a
wick, the salts naturally remain behind on the surface as the water evaporates, the
process only stopping when the moisture in the soil is exhausted. We thus not
infrequently find that after an unusually heavy rainfall there follows a heavier
accumulation of alkali salts at the surface, while a right shower produces no per-
ceptible permanent effect. We are thus taught that, within certain limits, the more
water evaporates during the season the heavier will be the rise of the alkali ; pro-
vided that the water is not so abundant as to leach the salts through the soil and
sub-soil into the subdrainage.

Leaky Irrigation Ditches. — Worst of all, however, is the effect of irrigation ditches
laid in sandy lands (such as are naturally predominant in arid regions) without
proper provision against seepage. The ditch water then gradually fills up the entire
substrata so far as they are permeable, and the water-table rises from below until
it reaches nearly to the ditch level, shallowing the subsoil, drowning out the deep
roots of all vegetation, and bringing close to the surface the entire mass of alkali
salts previously diffused through many feet of substrata.

An effect similar to that described in the last paragraph is sometimes
seen in the case of young seedlings, as in seed beds of eucalyptus or
orange trees, grown in soil containing a considerable amount of alkali or
salt, especially if they are watered with water of a similar nature. In
such cases the young plants frequently begin dying in a manner very
similar to that produced by damping-off fungi. The natural tendency
for the grower is then to use less water and endeavor to keep the soil as
dry as possible, which in the present case has the effect of increasing
rather than preventing the injury, since the injurious salts tend to
accumulate by evaporation about the stem of each seedling. As to the
best method of procedure in such cases, assuming that the trouble is
known to be due to injurious salts and not a case of true damping-off
caused by the fungi, we may again quote from Hilgard (p. 249) :

Mode of Using Saline Irrigation Waters. — The fact that abundant growth of
native as well as cultivated plants may sometimes be seen on the margins of "alkali
lakes" where water of over a hundred grains of mineral salts per gallon continuously
bathes the roots, while the same plants perish at some distance from the water's
edge, points the way to the utilization, in emergencies, of fairly strong saline waters,
viz., by the prevention of their concentration to the point of injury by evaporation.
It is clear that when such waters are used sparingly, so as to penetrate but a few
feet underground, whence the moisture re-ascends for evaporation at the surface, a
few repetitions of its use will accumulate so much alkali near the surface as to bring
about serious injury. If, on the other hand, the water is used so abundantly that
the roots may be considered as being, like the marginal vegetation of alkali lakes,
bathed only by water of moderate strength, no such injury need occur ; and what
does accumulate in consequence of the inevitable measure of evaporation occurring
in the course of a season, may be washed out of the land by copious winter irrigation.

This, of course, presupposes that the land, as is mostly the case in the arid
region, is readily drained downwards when a sufficiency of water is used. When
this is not the case, e. g., in clay or adobe soils, or in those underlaid by hardpan,
waters which in sandy land could have been used with impunity, may become inap-
plicable to irrigation use.

Apparent Paradox. — Tne prescription to use saline waters more abundantly than
purer ones, in order to avoid injury from alkali, though paradoxical at first sight, is

1066 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

therefore plainly justified by common sense as well as by experience, in pervious
(sandy) soils; while in difficultly permeable ones, their use may be either wholly
impracticable, or subject to very close limitation.

Sometimes the alternate use of pure and salt-charged water serves to eke out a
too scant supply of the former. But in all such cases, close attention to the measure
of water that will wet the soil to a certain depth, and "eternal vigilance" with
respect to the accumulation of alkali near the surface, must be the price of immunity
from injury. In all cases the farmer should know how much of alkali salt he
introduces into the land with the irrigation water, and watch that it does not
approach too closely, or exceed, the tolerance of his crops for alkali salts.

A proper discussion of the methods of utilization and improvement
of alkali lands would be too extensive to include in a publication of this
sort. The subject is very fully treated by Hilgard, pages 422 to 484.
We may say, in a general way, that the possibilities in this direction lie,
first in the planting of crops most resistant to such conditions, since
cultivated plants vary widely in this respect. The date palm, for
instance, grows and flourishes in soil where almost no other cultivated
plant can maintain its existence. The grapevine and olive are also
highly resistant, while the peach, apricot, and prune are much more
sensitive. The specific substance present in the soil, whether sodium
carbonate (black alkali), sodium sulphate (white alkali), or sodium
chloride (common salt), is of great importance in this connection, as
the relative tolerance of various plants for these different salts varies
widely. It is also to be remembered that in the case of fruit trees
there is usually some choice in regard to the kind of root upon which
the trees may be budded or grafted, as the various roots vary consid-
erably in their tolerance of saline salts.

In addition to the possibilities of utilizing alkali lands by the choice
of resistant plants, the possibilities of reclaiming or improving such
lands lie mostly in the direction of dissolving out the injurious salts
by flooding with water, and then removing the water with the salts in
solution by drainage. Much good may be done in this manner where
an abundant supply of fairly pure water is available and the topography
of the land is such that drainage can be secured. Something can also
be done in the way of neutralizing or changing the composition of these
soils by application of chemical substances to the soil. It has been
demonstrated, for instance, that in the case of black alkali (sodium
carbonate), a change of this substance to white alkali (sodium sulphate),
can be effected by an application of gypsum, the sulphate being much
less injurious to vegetation than the carbonate. This whole subject is
discussed at length by Hilgard.

Acid Soils. — Vegetation is sometimes injured or its growth prevented
by an acid or sour condition of the soil. This is much less common in
California, however, than in the Atlantic States. It is more apt to occur
in wet, swampy land, or in recently cleared forest soils, where there is

Bulletin 218] CALIFORNIA PLANT DISEASES. 1067

a large amount of vegetable matter in the ground. Such a condition
can be definitely determined by chemical analysis.

Soil acidity is corrected by the application of lime. (See Hilgard,
pages 122 and 123.)

EFFECTS OF DRYNESS.

(The following discussion presupposes to a large extent the avail-
ability of water for irrigation purposes, yet it is to be remembered that
large areas of fruit tree and other crops are grown in California without
irrigation. What is said in regard to the use of irrigation water will,
of course, not apply in such cases. The grower of non-irrigated crops
must look to choice of soil and location and cultural methods of moisture
conservation. What is said in regard to physical soil defects as affecting
the moisture supply applies even more forcibly in this case than in that
where irrigation is practiced.)

Some of the greatest mistakes in California horticulture have been
made in the attempt to grow crops, particularly tree fruits, without
irrigation. Many acres of dying or dead, abandoned orchards still
remain to testify to the disastrous results of such experiments. Further-
more, it may be said that even in the case of a large acreage of orchard
fruits which is still being cultivated and producing fairly profitable
returns, such returns would be very much greater if water for irriga-
tion were available. Even in cases where irrigation might not be neces-
sary every year, a possible source of water supply to be drawn upon
during dry years would be the most valuable form of insurance which
the grower could obtain. There are many orchards and large areas of
land in California where good returns are obtained year after year
without irrigation, yet even in the most favorable cases as the trees
grow older, filling the soil with roots, drawing more completely upon
its moisture content, and demanding more and more water as the tops
grow larger and the crops greater, the desirability of irrigation is likely
to become more or less pronounced. Nothing should be considered more
seriously by the intending planter than the water question, and he
should undertake planting without the possibility of irrigation only
with the utmost conservatism.

No doubt more trouble and failure in cultivated plants is caused in
California from lack of soil moisture than from any other influence.
While it would seem that so simple a cause would be readily seen and
remedied, yet it is a fact that under our semi-arid conditions, where
irrigation during most of the growing season is usually an absolute
necessity, a lack of a sufficient amount of water quite unsuspected by
the grower is one of our most common troubles. It is due in some cases
to an insufficient supply of available water, making it impossible to
obtain the necessary amount, but more often to a failure of the grower

1068 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

to realize or examine the condition of the soil beneath the surface, and
a failure to apply the necessary amount of moisture or to use methods
which would insure its absorption by the deeper layers of soil. In our
citrus groves, for instance, no experience is more common in examining
trees supposed to be suffering from some mysterious disease, than to dig
down three or four feet or less below the surface and find the soil
entirely dry, much to the surprise of the owner. Sometimes, also, in the
case of deciduous as well as citrus groves, in the winter when rainfall
is commonly expected to provide sufficient moisture, the subsoil may be
found extremely dry because the usual amount of rain has not occurred.
Trees often suffer severely from this cause, even when in a dormant
condition. Particularly in the fall, after the crop and leaves are off,
deciduous orchards often go for many weeks without rain or irrigation,
the grower failing to realize that the trees need a plentiful supply of
water even though they are not growing or carrying a crop of fruit.
Severe injury is frequently caused in this manner to walnut, apple, and
other similar trees, which injury shows itself in a poor crop or die-back
condition the following season.

In citrus groves the uncertainties of our rainy season lead often to
equally bad results. The usual practice in citrus irrigation consists in
an application of water about every thirty days, on the average, during
the dry summer season, which application is supposed to be supple-
mented by copious rainfall during the winter months. Such rainfall
is expected to soak the ground more completely and deeply than can
ordinarily be accomplished by irrigation, and is counted upon partic-
ularly to create a subterranean store of moisture in the subsoil. The
citrus grower expects, in an average season, sufficient rainfall to make
irrigation unnecessary during a period extending from about November
first to May first. Relying upon such an expectation his tendency is
to withhold irrigation after October, waiting for the expected rain, and
to put it off as late as possible in the spring for the same reason. The
grower of deciduous fruits, whose crop comes off in the summer and
whose trees are leafless and dormant during the winter, stops irrigating
still earlier and is apt to pay little attention to his trees after the crop
is gathered.

Most seasons this confidence in the elements is not misplaced, rain
coming soon enough and late enough to prevent serious damage. From
time to time, however, a season occurs when the rain does not come on
schedule time in the fall, or the rainy season ceases unusually early in
the spring. In such seasons the grower, with each day's waiting, is
more and more certain that rain will come and continues to postpone
irrigation. Serious injury is sometimes caused in this way and one
which may lead to more obscure after-effects, such as die-back, gumming,

Bulletin 218] CALIFORNIA PLANT DISEASES. 1069

mottled leaf, and other pathological symptoms. Particularly when a
dry fall follows a dry spring, making nearly a year without rain, is
this sort of trouble likely to occur. In such a season, even with more
irrigation than usual, the soil does not get the deep soaking which only
long, heavy rains can give it, and the subsoil is likely to dry out. This
condition is most pronounced, naturally, on soils underlaid with a porous
subsoil not having the greatest water-retaining capacity, or where there
is hardpan or other hard material beneath the surface, preventing a
deep soaking-in of the water. The average irrigation comes far from
equalling a good rain in wetting the ground. "When the winter rain is
up to or above the average in amount and distributed over its normal
season, groves which receive even tolerable irrigation, upon soil of even
moderate water-retaining properties, may go through in fairly good
condition. Following the dry seasons the groves where the subsoil
dried out begin to show up and exhibit signs of distress. In the very
driest years this may extend to groves upon soil which ordinarily is
considered to have good water-retaining qualities.

The effect of frost and cold weather is much more decided on trees in
this dry condition than upon those which have their tissue filled with the
proper amount of moisture, and numerous instances are to be seen of
severe frost injury to citrus and deciduous trees in groves allowed to
become extremely dry in the fall, while neighboring groves, which
receive proper irrigation, are entirely unaffected.

A dry condition of the subsoil is frequently brought about, even
where the amount of water available is sufficient, through faulty physical
conditions such as hardpan, soils underlaid with rock close to the
surface, sandy or gravelly subsoil, or other similar conditions which
prevent the retention of a proper amount of moisture several feet below
the surface of the ground. All sorts of conditions may occur which
have this effect of limiting the moisture supply available to the roots,
and, as we have just said, nothing is more common in California than
to find plant troubles due to this cause. This is one of the most impor-
tant reasons, therefore, for digging down into the soil to an ample depth
in investigating cases of failure or poor development.

In some parts of the State, particularly in the northern portion, a
very irregular soil moisture condition occurs, due to the combination of
a heavy winter rainfall and a very dry, hot summer, with a porous,
gravelly soil more or less underlaid by hardpan. In such regions the
soil becomes extremely wet in winter and if hardpan exists near the
surface the water does not drain away but the soil remains saturated
clear to the surface. After the rains cease, however, the moisture dries
out rapidly, so that during the summer the dryness of the soil reaches
an equally extreme stage. Large areas of orchard have been planted

3— Bul. 218

1070 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

under conditions similar to this without irrigation under the impression
that no irrigation would be needed, on account of the large amount of
rainfall and the extremely wet condition of the soil during the winter.
Such plantings, however, have in every case resulted in absolute failure,
except where subsequently a permanent water supply for irrigation was
secured. The trees linger along for a few years, making a fair growth
at first, but ultimately becoming stunted, affected by die-back, and finally
dying completely, except in the case of the most drouth-resistant species.

The remedy for such troubles is usually obvious, consisting in choos-
ing, so far as possible, deep soils with fairly heavy subsoil, and in
obtaining a sufficient water supply, using methods for its distribution
and application which will insure a proper moistening of the soil to a
sufficient depth. When trouble of this sort is once realized it is in many
cases not difficult to remedy it by proper cultural methods, if the soil is
of proper quality and particularly if sufficient water for irrigation is
available. Again we would say, however, that a failure to examine the
subsoil by deep digging and a consequent lack of knowledge of its
moisture condition is one of our most common causes of tree failure.
Frequently, even at the very time of irrigation, when the surface soil
was saturated and covered with water, it has been found that at a depth
of two or three feet the ground was completely dry on account of a plow-
sole or hardpan which prevented the water from soaking down to a
proper depth. It will be seen from what has been said that this sort of
trouble may occur from one of two causes : either from a too porous sub-
soil with insufficient water-retaining quality, or from a hard layer
beneath the surface which does not allow the proper penetration of
water.

The methods of improving these conditions are considered in another
chapter, see page 1074. It is obvious that the remedy lies on the one
hand in adding humus or organic matter to the lighter soils to make them
hold water better, and on the other hand in breaking up the hard layer of
subsoil in order to allow the water to penetrate more rapidly and deeply.
Beyond these methods of soil improvement there must also be considered
the methods of irrigation best adapted to each condition. In order to
keep more moisture in the soil there are three possibilities in addition
to what may be accomplished by cultural means : either more water must
be put on at the usual time of irrigation, or the water must be put on
more frequently, or the irrigation season must begin earlier or be ex-
tended later to connect more closely with the rainy season. It may, for
instance, be necessary with an orchard having a light, porous subsoil,
especially in a dry season, to irrigate oftener than every thirty days, if
the water can be obtained, or to irrigate earlier or later in the season
than is customary. On heavier soils, or where it is impossible to get

Bulletin 218] CALIFORNIA PLANT DISEASES. 1071

water other than at the regular time, it may be possible and effective
to put on more water than has been the practice. It is easier and
cheaper, of course, to put on larger amounts of water at longer intervals
rather than smaller amounts at shorter intervals. The former method is
also more likely to conform with the established regulations in most irri-
gation districts. Such considerations and the water-retaining capacity
of the subsoil must govern the grower.

In addition to the moistening of the soil by irrigation, there must not
be forgotten the possibilities of preventing surface evaporation by fre-
quent cultivation. This leads us, however, too far from our subject,
and we must leave the matter with this suggestion. Most important of
all is for the grower to know definitely the moisture condition of the
soil at all times down to a depth of at least four feet, disregarding
entirely the appearance on the surface, and irrigate accordingly.

EFFECTS OF EXCESSIVE MOISTURE.

Although a lack of moisture is so common in our cultivated soils, yet
cases are also quite common and sometimes entirely unsuspected where
there is too much water in the subsoil, and vegetation suffers accordingly.
This, again, can be easily determined by digging a hole down to the
depths of the lower roots and examining the condition of the soil as to
moisture. In some regions the natural water level is near the surface,
and this fact must be kept in mind and the level of the water accurately
determined before making extensive plantings. Again, through irriga-
tion or otherwise, the water level may be raised, either in the hollows and
lower spots of a region where the surface is uneven, or under the whole
surface of large areas where the surface is level. The latter case has
already been alluded to in our discussion of alkali soils and the rise of
water in the same, page 1064. Many large areas of good land in Cali-
fornia have been rendered almost worthless in this manner and often this
condition has come about and orchards and other plantings been severely
injured before the true condition was realized by the owner. Here,
again, the simple process of digging a hole to a depth of several feet
in the ground is sufficient to indicate the cause of the trouble. Trees
affected in this manner usually begin dying in the top and at the ends
of the branches, the leaves developing poorly, turning yellow and falling
off as the die-back proceeds. The effect is very similar to that produced
by dryness of the soil, and, in fact, the effect upon the parts above
ground is practically the same in either case. If the soil is too dry, the
top suffers because the roots can not send up the proper amount of
moisture, while if the soil is too wet the roots are injured and killed and
again the top fails to receive what it should from the roots.

One of the worst troubles of this sort is experienced in cases where the

1072 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

water level does not remain constant, either high or low, but rises and
falls a considerable number of feet during the year. This is a condition
of quite frequent occurrence in some sections, particularly in the vicinity
of large, uncemented irrigation canals in sandy soil. In such places
the water level of the surrounding country may come up nearly to the
surface of the ground during the irrigation season when the canals are
constantly full of water, while after the water is shut off its level in the
soil goes down for many feet. Under such conditions, the roots have no
opportunity to accustom themselves to development at a certain level,
but are continually subjected to alternate flooding and drying. Such a
condition can be determined by digging an open pit or well to a depth
of 10 or 15 feet, and watching the fluctuation of the water level during
the season.

The only remedy for all these conditions consists in drainage to pre-
vent the water rising above a certain level, and, in the last instance
described, in cementing the bottom and sides of the main ditches so that
seepage can not occur. The latter is expensive but is the only means of
stopping the widespread injury of this sort, which is at present occurring
in some regions.

EFFECTS OF FAULTY PHYSICAL STRUCTURE.

Cultivated plants frequently suffer or die on account of unfavorable
conditions of structure or formation of the subsoil. Nothing is more
fatal to the success of the land-seeker in California than to judge the
value of a piece of ground by the nature of the surface soil. By digging
or boring down to a depth of a few inches or feet he may encounter
something entirely different from that seen on top, and something which
would doom his proposed planting to absolute failure from the very
start. Again, plantings may be made and flourish for a time, but then
begin to fail as the roots reach the unfavorable conditions below.

Faults of this sort are most commonly of two general classes, namely,
the subsoil is either too hard and impenetrable, preventing the roots
from developing properly and limiting the supply of moisture available
for them ; or it is too coarse and porous, being unable to retain moisture,
and deficient in plant food. In the former instance, on digging down
into the soil one may encounter at a slight depth solid rock, hard clay
(hardpan), or he may come into gravel, coarse sand, or some other
undesirable soil formation. Again, in the case of old, long cultivated
orchards, particularly in heavy soils, an artificial hardpan or plow-sole is
frequently formed on account of the gathering together of the finest soil
particles at a depth just below that reached by the plow and cultivator.
All of these conditions can be readily determined by digging or boring
down into soil.

The chief difficulty in this respect is that of judging accurately just

Bulletin 218]

CALIFORNIA PLANT DISEASES.

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1074 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

what degree of hardness or coarseness in the subsoil is undesirable or in-
jurious, or what conditions in these respects are desirable and favorable
to plant life. On the one hand, the heavier the soil the better it will
retain moisture and plant food, so long as it is not so extremely hard or
impervious as to prevent its being penetrated by roots and water. On
the other hand, the heavier the soil the more difficult it is to cultivate,
while if it is sandy and porous it is easier to handle, takes up water more
readily, and is more easily penetrated by plant roots. On lighter soils
plants usually respond more promptly to applications of water and
plant food ; such soils are easier to plow and cultivate and can be worked
at any time of year, while heavy soils present an opposite condition in
these respects. Furthermore, different kinds of trees and plants vary
widely in their adaptability to heavy or light soils, or the depth of soil
which they require for proper development. Soils which are entirely
too light or too shallow for one kind of tree may be entirely fitted for
another kind. Altogether, therefore, one may not judge too hastily or
be too quick either to condemn or approve a soil for a certain plant
without large experience, and expert knowledge of practical conditions
and results in this respect.

The methods of improvement of soils of poor mechanical structure
form a subject in themselves too extensive to be taken up in this place.
Such improvement must be mainly brought about in one of two ways :
First, through cultural operations, such as deep plowing and special
cultivation; second, by adding materials to the soil, such as straw,
manure, or green manure crops. Special treatises on this subject should
be consulted for information along these lines.

In the case of hardpan of limited thickness underlaid by good soil,
the radical practice is sometimes resorted to of blasting with powder or
dynamite, blowing out a hole for each tree before it is planted. Even
in established groves, blasting between the trees is sometimes done with
good results. ( See Hilgard 's ' ' Soils, ' ' page 181. )

Artificial Influences in the Soil. — Injury to plants sometimes occurs
through the presence in the soil of injurious substances which have come
there artificially through drainage, or by being placed in or upon the soil.
These may be waste substances from manufacturing or result from any
one of a great variety of causes, sometimes wholly unsuspected. As an
instance of this, we may cite injury to citrus trees which sometimes
occurs from the pouring upon the ground of the residue of sulphuric
acid and potassium cyanide remaining after the process of fumigation
for killing scale insects. Sometimes a single root or one side of the
trunk will be affected by some injurious substance of this sort, and the
injury reflect itself in only one limb, or on one side of the tree corre-

Bulletin 218] CALIFORNIA PLANT DISEASES. 1075

sponding to the injured portion of the root or trunk. Some very mys-
terious cases of tree disease have been traced to this source.

A not infrequent source of injury to trees, particularly street trees,
is the presence in the soil of illuminating gas escaping from leaky pipes.
Great damage has resulted to the street trees of many cities from this
source. In any case, where street trees commence to fail and die from
no apparent reason, this sort of trouble should be looked for if there is
a gas pipe in the street.

INJURIES BY ANIMALS.

Various animals are injurious to cultivated crops, but their effects
and remedies are mostly obvious, and need no special consideration.

The most serious injury of this sort in California is that produced by
the common gopher, which is one of our greatest pests. These animals
feed upon the roots of all sorts of cultivated plants and trees, and under
favorable conditions become very numerous. Their most evident effects
are seen where plants suddenly wilt and die on account of the roots being
eaten off. In the case of orchard trees of considerable size, the gopher
often works on the bark of the main roots, causing the tree to gradually
decline and its foliage to become yellow, finally bringing about the death
of the tree. It may linger along for several years, however, before be-
coming entirely dead. In citrus groves, especially where gopher control
has been neglected, trees are frequently seen with foliage of a bright
yellow color and covered with an abnormally large number of small
fruits. Such trees are an almost invariable indication of gopher attacks,
and, if not taken in hand very promptly, will soon be killed. If, how-
ever, gophers are gotten rid of before the injury to the roots has gone
too far, the tree may form new bark and finally recover. In such cases,
it is well to cut the top back to an extent proportionate to the amount
of injury and thus give the tree a better chance to recover.

Gophers can only be kept down by constant warfare through the use
of traps, poison and shooting. Special traps and poisonous preparations
are made for this purpose, some of which are very effective. See bulletin
172, "The Pocket Gopher," Kansas Experiment Station, Manhattan,
Kansas.

Squirrels, moles, and other similar animals often cause much damage
to vegetation and are to be controlled by means of the nature just
alluded to, namely, poisoning, trapping, and shooting. See Circular
76, "The California Ground Squirrel,' ' Bureau of Biological Survey,
United States Department of Agriculture. See, also, Wickson 's ' ' Cali-
fornia Fruits,' ' page 410, for methods of control of gophers, squirrels,
rabbits, etc.

In regard to rabbits, we quote the following from the "California
Cultivator' ' of March 23, 1911 : "According to the experts of the North

1076 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Dakota Agricultural College, damage to trees by rabbits gnawing the
bark can be stopped in the following way: Make a thick whitewash;
slaking the lime over night improves it. To each pailful of the white-
wash add three tablespoonfuls of paris green, and paint the trees with it.
Stir frequently when applying it. ' '

Insects. — The control of insect pests will not be considered in this
bulletin. This is a large subject in itself and publications are available
covering most of our common pests.

Worms. — One organism of this group is of particular importance in
connection with California plant diseases, namely, the Nematode Root
Worm, Heterodera radicicola. This is a worm of microscopic size, which
lives parasitically in the roots of many different plants, causing small
nodules or galls upon them. Such nodules are quite frequently seen
upon the roots of nursery stock, garden vegetables, and other plants,
but for some reason this organism does not seem to become serious in
this State. In the southeastern portion of the country it causes serious
damage to orchard trees and other plantings, but this does not seem to
be the case in California.

The organism in question is hatched from eggs which are deposited
by adult female worms in the root galls. These eggs hatch and the
young worms, which are so small as to be quite invisible to the eye, move
about in the soil for a few days but soon burrow into the tips of young
roots where they come to rest. By their presence in the roots they cause
an irritation which produces a swelling and the formation of galls. The
mature female worms can be seen with the naked eye by careful exam-
ination, being little, pearly-white, pear-shaped bodies, about the size of
small pin head. They may be found embedded in the tissues just
beneath the surface of the galls.

This form of injury is alluded to more specifically in connection with
various plants in a later portion of this bulletin.

Slugs and Snails. — These creatures are frequently the cause of much
damage to plants, especially in moist weather. They are best controlled
by sprinkling dry lime dust upon the ground in circles about the plants,
upon the leaves of the plants themselves, or in any way so that the slugs
will be obliged to come into contact with the lime. This is very repulsive
to them on account of its irritating effect upon their soft bodies. They
may also be trapped to some extent by laying boards upon the ground
in the vicinity of the plants upon which they feed, thus affording a
shelter under which they may be found and killed. It is said that ducks
are particularly fond of these creatures.

In regard to snails, we find the following in the Pacific Rural Press,
of June 12, 1909, page 439 : 'These pests are quite common in England

Bulletin 218] CALIFORNIA PLANT DISEASES. 1077

and in English gardeners ' experience a mixture of salt and soot scattered
upon the ground which they traverse seems to be most effective. Lime,
which is something of a protection against the slug branch of the snail
family, does not seem to be objectionable to the shell bearer."

Fungi, Bacteria, and Slime Molds. — Organisms of this sort are the
cause of most of our specific plant diseases, and these are described in
connection with their particular host plants in the following alpha-
betical list. A short description of the general nature of these organisms
may be useful at this point.

Fungi. — The organisms called fungi are true plants but of a very
low order. The largest and most highly developed members of the
family are represented by the toadstools, mushrooms, and similar plants.
Other common examples of fungi are the various molds and mildews
often seen growing upon different organic materials, especially in moist
air. Only certain fungi are injurious to vegetation. Those species
which are not are called saprophytes. These grow upon dead material,
like the toadstools which we see upon dead wood or manure and the
molds which develop upon decaying fruit, moist leather, bread or jelly.
Many kinds of fungi, however, are able to grow only upon the tissues
of living plants. These are called parasites. Examples of this are
seen in the rose mildew, a mold-like fungus which can not live except
upon living leaves, and the various rusts which have the same habit.
In the case of the rust most of the fungous plant develops in the interior
tissue of the leaf, while in the rose mildew it grows mostly upon the
surface.

It is characteristic of parasitic fungi that in most cases each particular
species of fungus has a particular species of plant which it attacks, or
its attacks are limited to a few closely related plants. Certain species
of rust, for instance, attack only a few of the grains or grasses. Another
species of rust attacks the asparagus, but the asparagus rust fungus
can not develop upon grain nor the grain rust upon the asparagus plant.
Some fungi are both parasitic and saprophytic, being able to grow
either upon living plants or dead matter. Others are mainly sapro-
phytic but may become parasites upon plants in a weakened or un-
healthy condition.

The body of a fungous plant consists usually of a branching mass of
very fine, thread-like filaments called the mycelium. In toadstools
the mycelial filaments become very abundant and mass together into
structures of considerable size and definite form. In the mold fungi
the mycelium develops abundantly under favorable conditions and
makes a cobweb-like or cottony mass. In most of the parasitic fungi
the filaments of the mycelium grow through the interior tissues of the
plant attacked (called the host plant) and at the same time withdraw

1078 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

nourishment for their own use. They also sometimes secrete poisonous
substances, and thus are caused the leaf spots or dying of whole leaves
which we see resulting from fungus attacks. Some fungi also cause
active decay of fruit, fleshy roots, tubers, wood, and other vegetable
material. The reproductive bodies of fungi, corresponding to the seeds
of higher plants, are called spores. These are usually very small, dust-
like particles, each of which is capable of sprouting and reproducing the
fungus if it finds favorable conditions. In the case of the rusts we see
the spores as a dusty powder which develops on affected plants. Most of
the common molds also produce a dusty mass of spores on the surface
of the mycelium.

The control of fungus diseases by spraying is almost always effected
by covering the plants with the poisonous material before the fungus
has made its attack, thus killing the spores before they can send out
sprouts and reach the interior tissues. If the latter has been accom-
plished and the fungus is already inside the plant nothing can then be
done to stop its effects save by preventing its spread to other leaves or
plants not yet affected.

Bacteria. — The bacteria are organisms of even simpler nature than
the fungi, having no mycelial body, but consisting of very minute, indi-
vidual particles. Each of these individuals is able to multiply very
extensively and rapidly by division, so that under favorable conditions
bacteria can develop in sufficient abundance to form a mass visible to
the eye. Such a mass of bacteria is usually of a slimy nature, as seen
in fruit and vegetables which have become so thoroughly decayed as to be
in a semi-liquid condition. Most of the bacteria are purely saprophytes,
living only on dead matter and producing by their growth decay, fer-
mentation, putrefaction and similar processes. A number of species,
however, are parasitic on animals, causing many of the commonest and
most serious human and animal diseases. The bacterial plant parasites
are fewer in number, although the list of bacterial plant diseases is
gradually growing. Some of the most conspicuous examples, like the
pear blight and walnut blight, develop in the fresh, succulent tissues
of the bark or in the fruit, causing the death of the parts affected.

It should be said in connection with fungus and bacterial diseases
that the mere finding of an organism of this sort upon a diseased plant
or any of its parts is by no means proof that the organism found is the
cause of the trouble. If a leaf, for instance, is injured in any way so
that its vitality is almost or quite destroyed, various kinds of sapro-
phytic fungi or bacteria usually develop upon it very quickly. If a
plant dies or becomes very much weakened from any cause its roots soon
begin to decay and various saprophytic soil fungi and bacteria will be
found in its tissues. It is practically impossible for dead or dying plant

BULLETIN 218] CALIFORNIA PLANT DISEASES. 1079

tissue, no matter how it was first affected, to remain in existence without
falling prey to all sorts of fungi and bacteria which would have no
power whatever of developing upon the same plant when in a healthy
condition. The plant pathologist must, therefore, proceed with extreme
caution to attribute plant troubles to organisms of this sort until he has
absolutely proven that the initial injury was produced by the organism
under suspicion, when the plant was still in a healthy condition. To
make this absolutely certain, he must not only find the organism upon
the plant, but must also produce all the characteristic symptoms of the
disease by inoculating healthy plants of the same species with his fungus
or bacterium. Long experience may make this unnecessary at times
and obviate much tedious work, but the young investigator is more apt
to err in the other direction, attributing plant troubles to fungi or
bacteria which really had nothing to do with them.

Slime Molds (Myxomycetes) . — A few plant diseases are caused by
organisms of this class. They are grouped at the very bottom of the
vegetable kingdom, and comprise some of the simplest forms of life.

A LIST Of THE MORE SPECIFIC PLANT DISEASES IN CALIFORNIA,
WITH BRIEF DIRECTIONS FOR TREATMENT.

ALFALFA.

Crown Gall (Urophlyctis alfalfw). Figure 7.

Gall-like swellings appear on the stems and main roots just at the
surface of the ground and the plants die. The trouble is favored by
excessive moisture in the soil. Caused by a fungus. This is a new
disease in this State, and has not been reported elsewhere in the country
at this writing.

Allow the ground in affected spots to dry thoroughly and do not use
it again for some time.

Leaf Spot (Pseudopeziza medicaginis) . Figure 8.

The leaves turn yellow and die, with small, dark spots upon the
surface. The trouble is not a serious one in this State, and needs no
special treatment. Caused by a fungus.

Cut and burn the crop if badly affected.

Rust (Uromyces striatus) .
Reddish-brown, dusty pustules break out in small spots on the surface
of the leaves. This trouble is caused by a true rust, and sometimes
becomes quite destructive to alfalfa during the rainy season. It in-
variably disappears with the coming of dry weather, so need not be
seriously feared.

Cut and burn badly affected crops.

1080

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Fig. 7. — Crown gall of alfalfa (Urophlyctis alfalfae),

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1081

Stem Rot (Sclerotinia libertiana).
The stems wilt and die after reaching nearly full size. Usually scat-
tering stems here and there about the field are affected, and may be
easily seen by their contrast with the thrifty, green appearance of the
other stalks. This trouble usually occurs most abundantly where there
is a thick stand of alfalfa, heavily shading the ground, particularly in
the spring when the ground is very moist. On pulling an affected stem
it is found to be decayed at the base, and usually shows a more or less
abundant white mold upon the surface if there is an abundance of
moisture. In this mold small, roundish, black bodies develop, which
represent one stage of the fungus. This is apparently the same fungus
which causes the cottony mold decay of lemons (page 1123) and also

Fig. 8. — Leaf spot of alfalfa (Pseudopeziza
medicaginis ) .

stem rot of various other plants. It causes considerable damage to
alfalfa at times in this State, and it has been reported as a serious
disease in other States. The fungus is common, affecting various plants
all over the world.

No specific remedy can be suggested, but the disease usually disap-
pears to a large extent during the summer and fall. Badly affected
fields should be plowed up and used for some other crop for several
years.

1082

UNIVERSITY OP CALIFORNIA — EXPERIMENT STATION.

Fig. 9. — Shot-hole of almond (Cercospora circumscissa) .

Fig. 10. — Almond rust (Puccinia pruni),

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1083

Dodder (Cuscuta).

A thread-like, yellowish vine forms a thick mat in the alfalfa, and
becomes parasitic upon it. It is a true flowering plant. In badly
affected fields a large proportion of the crop is lost from this source.
Allow the field to dry out for some time and the dodder will often

Fig. 11. — Crown gall of almond (Bacterium tumefaciens) .

be entirely killed without destroying the alfalfa roots. If the field is
badly affected plow and replant later.

Avoid planting infested seed. Dodder seed is often mixed with that
of alfalfa.

ALMOND.

Shot-hole (Cercospora circumscissa) . Figure 9.

There appear on the leaves numerous, small, dead spots, which finally
fall out, giving a shot-hole effect. The young twigs are also spotted.
The trees are sometimes defoliated early in the season by this fungus
and the crop badly injured.

Spray with Bordeaux mixture in the spring as the buds are opening.

1084 UNIVERSITY OP CALIFORNIA — EXPERIMENT STATION.

Rust (Pnccinia pruni). Figure 10.

Red or brown, dusty pustules appear on the under side of the leaves,
usually late in the season. The fungus may hasten the normal dropping
of the leaves somewhat but is not serious on thrifty trees ; worse where
the trees suffer from drouth.

No treatment ordinarily needed.

Crown Gall (Bacterium tumefaciens) . Figure 11.

Large swellings appear on the main root just below ground and to
some extent on the smaller roots. This results in a gradual failure
and dying of the trees. This is one of the commonest troubles of our
stone fruit trees, being found both in the nursery and on mature orchard
trees. This trouble is caused by a bacterial organism which infests the
soil. The organism would seem to be abundant in California soils,
since cases are not rare of infection on the roots of trees grown from
pits in virgin soil.

Avoid planting nursery trees in affected ground and in orchard
planting discard every tree which shows any evidence of this trouble.
On old trees the galls may sometimes be chiseled off after digging down
and exposing the main roots, but this treatment is not usually very
satisfactory. Disinfect the cuts with strong bluestone or corrosive
sublimate solution.

Root Rot — Oak Fungus. Figure 12.

Many orchards of almonds and other trees contain certain spots
where the trees commence dying from a center, the trouble gradually
proceeding outward in a circle, involving tree after tree. Clusters of
toadstools frequently appear about the base of affected trees in the
winter. These spots usually coincide with places where oak trees
formerly stood and the destruction of the fruit trees is due to certain
' ' toadstool ' ' fungi which apparently live on the old oak roots and spread
through the soil, infecting the roots of the orchard trees. Several dif-
ferent fungi seem to cause this disease, among which Armillaria mellea
is probably the most important.

The progress of the trouble may be checked by digging a deep trench
around the affected area, but this is impracticable in most cases.

The development of a resistant root presents the only practical
remedy.

The pear root, fig and that of the California black walnut are some
of the most resistant among fruit-bearing trees and these may usually
be planted with safety. The cherry is the most resistant of the stone
fruits.

Fruit Drop.

The fruit falls to the ground while still very small and undeveloped.
Due partly to seasonal conditions which can not be controlled, and
partly to a lack of cross pollination, which can be secured by mixing

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1085

varieties in planting. Heavy rains at the time of blossoming may have
this effect, and it may also be produced by frost, killing the young germ
in the seed of the fruit. Many other fruits are affected in the same
way, such as the apricot, cherry, peach, and pear. The fruit may
remain on the tree and continue to grow in size for some time before
dropping.

Fig. 12. — Root rot caused by the toad-stool fungus (Armillaria

mellea) on live oak.

Sour Sap.
"When affected with this trouble the tree may suddenly die just as it
is coming out in the spring in full vigor, or the effect may be limited
to one limb or one portion of the tree, which dies after the leaves have
started, or even after the fruit is partly grown. All our stone fruits
suffer frequently with the disease characterized by this name, while
4— Bul. 218

1086

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

occasionally the pear and other trees are affected. The trouble appears
to be due entirely to climatic conditions resulting from a combination
of unseasonably warm, balmy weather in winter, followed by a marked
change to colder weather. The sap of these trees frequently starts into
active circulation with the first approach of spring, and when this
occurs too early in the season, cold weather following suddenly, checks
the flow of sap and other functional activities of the tree, causing a
stagnation and finally fermentation.

Affected trees should be pruned back to healthy wood, where there is
enough remaining to make a new top.

Fig. 13. — Die-back of orchard trees.

Die-Back.
Numerous more or less abandoned groves of almonds, as well as other
deciduous fruit trees, are to be seen in California which present a dis-
tressing appearance on account of a dying back of the branches. In
some cases the trees are entirely dead, while in others they show all
stages of deterioration. The trouble in the majority of these cases is
due primarily to a lack of water induced by a variety of causes, either
an absolute lack of sufficient moisture during the year to keep the trees
alive, or unfavorable soil conditions, such as hardpan, gravel, and similar

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1087

troubles. Lack of soil fertility is frequently a contributory factor.
Such cases of die-back are connected usually with some of the unfavor-
able soil conditions which we have described in connection with that

Fig. 14. — Apple twig affected by mildew (Podosphaera oxyacanthae) .

subject. In the majority of cases these plantings were doomed to failure
from the start and represent an ill-advised undertaking, or in some cases
criminal deception. Various secondary causes may contribute to the

1088

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

dying of such trees as we have described, but such factors are usually
of little importance, and in many cases are an actual blessing to the
owner in hastening the time when his expenditures for the maintenance
of such an orchard are brought to an end.

APPLE.

Mildew (Podosphacra oxyacanthw) . Figure 14.
Characterized by a dwarfing of the tips of the new shoots, which,
together with the leaves which they bear, remain stunted and covered

^WHfh, ,1

Fig. 15. — Apple scab (Venturia inaequalis) .

with the white mildew growth of the fungus. Much worse on some
varieties than others.

Has not been controlled very successfully heretofore, but good results
have been obtained in some instances by spraying quite frequently
through the early part of the season, commencing just before the buds
unfold, with sulphide sprays. (See page 1187.)

Some growers report success from spraying with the caustic soda-
sulphur spray, about 10 pounds of dry sulphur being added to each 50
gallons of spray.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1089

The iron sulphide spray mentioned on page 1187 is said to be partic-
ularly effective for mildew in the Pajaro Valley.

Scab (Venturia inaequalis) . Figure 15.

Easily identified by the scabby patches produced on the surface of the
fruit, in which the brown, velvety growth of the fungus can be seen.

Spray with Bordeaux mixture just as the buds are opening, again
after the petals fall, and once or twice at intervals later, where the
variety or location is particularly susceptible. Arsenate of lead or
paris green for codling moth may be combined with this spray.

Blight (Bacillus amylovorus) .

See pear blight, which is caused by the same organism. Blight is not
usually as destructive in apples as in pears, except occasionally with
very susceptible varieties. Its worst effect in apples usually consists in
killing the blossoms and thus destroying the crop, rather than causing
the death of large limbs or whole trees. Sometimes the disease runs
down into the large limbs and may remain alive there from year to year,
forming a source of infection to neighboring pear and apple orchards.
More often the infection proceeds only to the base of the fruit spurs,
killing the twigs to that point.

Destroy old, worthless apple trees standing in the vicinity of valuable
apple or pear orchards.

Root Hot.
The " toad-stool' ' disease, described for the almond, occasionally
affects young apple trees recently set out, but it is not usually serious
on established trees.

Stem Rot (Schizophyllum commune) . Figure 16.

. This is another toad-stool disease, affecting the tree above ground.
The fungus in question shows itself in clusters of small, bracket-like
growths which appear on dead portions of the trunk or branches. This
fungus infects the tree through wounds caused by pruning or any
injury and in some cases develops rapidly in the heart wood of young
trees, extending far up in the trunk and out into the branches, while
the bark is still green and healthy and the whole tree appears to be in
good condition. From the heart wood the fungus gradually works out
into the outer sap wood and cambium, killing the tree. Affected trees
often appear in good condition at the end of the growing season in the
fall, but are found to be dead the following spring when they fail to
leaf out. This sudden effect is produced by the development of the
fungus into the sap wood and cambium during the winter while the
tree is dormant and more susceptible.

Make all pruning cuts cleanly and close to the trunk, and paint over

1090 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Fig. 16. — Canker of apple limbs caused by the fungus Schizophyllum.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1091

the scars with thick lead paint. In cases of trees unavoidably injured
the wounds should be treated in the same manner as soon as possible.

Sun Burn. Figure 17.

The bark on one side of the
trunk dies and the wounds thus
produced frequently become in-
fected with the little Schizo-
phyllum fungus just described.
The apple is quite susceptible
to winter sun burn injury of the
trunk and large branches. Es-
pecially in the higher foothill
regions, where in late winter
and spring the days are hot
and the nights cold, trouble of
this sort often occurs, as de-
scribed on page 1054.

Paint the trunks with thick
whitewash, and keep the
ground about the trees covered
in winter with vegetation or a
mulch of some sort.

Fig. 17. — Effect of sun burn on trunk of apple

tree.

Fig. 18. — Fruit spot of apple.

1092

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Die-Back. See Almond.
Fruit Spot. Figure 18.

Characterized by the appearance of sunken, discolored spots on the
surface of the apple, beneath which the tissue is found to be brown and
dead. The dead tissue also extends to a considerable extent in streaks
and lines through the flesh of the apple. This effect may show while
the apple is still on the tree or sometimes develops only after the fruit
has been picked for some time. The trouble has been ascribed to various
causes. This disease is similar to that called "brown spot" or "Bald-
win spot" in other portions of the country.

No cause or remedy satisfactorily demonstrated in California.

Fig. 19. — Storage spot of apple.
Storage Spot.

Numerous dark, dead spots appear on apples after being in storage
for some time, usually on the upper side of each apple as it lies in the
box. Especially common on the White Winter Pearmain, but also found
on Jonathan and other varieties.

Cause not definitely known, but in storage not due to freezing. Has
recently been attributed to after-effects of arsenical insecticides.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1093

Hollow Apple. Figure 20.
A peculiar condition found in one or two instances.. The affected
fruit is sunken in on one side and has a misshapen appearance. On
cutting through the apple large hollow cavities are found corresponding
to the sunken areas on the surface. Due apparently to some injury-
while the fruit was small.

Fig. 20. — Hollow apple.

Club Tip.

Terminal buds die back or fail to grow and enlarged swellings develop
at the ends of the living portion of the twigs. Lateral shoots may
develop later from these. Affects some varieties more than others.

Due apparently to unfavorable soil or climatic conditions which check
the growth of the terminal buds. Sometimes caused by apple mildew.
No remedy, save in latter case, which see.

Seasonal Effects. Figure 21.
Apple trees in California, particularly in the valleys, are sometimes
affected by the seasonal diseases described on page 1151. These effects
show themselves in die-back, blooming out of season, failure of the buds
to open at the proper time, " Little Leaf," and a stunted, weak growth
of the shoots. Such effects are produced most commonly, perhaps, by a
long, dry season in the fall, causing the trees to become especially dor-

1094

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

mant, followed by warm, spring-like weather during the winter soon
after the first rains. Again, they may be produced by long, continuous
rainfall during the winter, followed by a very sudden end of the rainy
season and a long period during the spring and early summer of hot,
dry weather. These, and other irregular combinations may produce
the effects described and other similar ones.

Fig. 21. — Little leaf of apple.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1095

APRICOT.
Shot-Hole and Fruit Spot (Coryneum beyerinkii). Figure 22.
This fungus is the same as that causing the peach blight and produces
in the apricot a spotting of the fruit, shot-hole effect in the leaves and
killing of the buds.

Spray with Bordeaux mixture during November and again in spring
just as the buds open.

See bulletin 203, page 33, California Experiment Station.

Fio. 22. — Apricot shot-hole and leaf spot (.Coryneum beyerinkii),

1096

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Fig. 23. — Apricot bud blight.
Bud Blight. Figure 23.
Characterized by a dying of the buds during the early winter and
caused very largely by the fungus just mentioned.

Similar trouble is caused more or less by "Sour Sap" conditions.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1097

Scab (Cladosporium carpophilum) . Figure 24.
Causes a scabby spotting on the surface of the fruit.
Has never been sufficiently serious to warrant treatment in California.

Brown Rot (Sclerotinia fructigena). Figure 20.
A decay of the fruit while still on the tree, occurring some seasons in
the vicinity of San Francisco Bay and other moist localities. The young
growth as well as the fruit is also sometimes affected, the new shoots
wilting and dying back from the attacks of this fungus. This is the
most serious obstacle to stone fruit production in the eastern states, but
does not find sufficient moisture for its development in California,

Fig. 24. — Apricot scab (Cladosporium carpophilum) .

except on early varieties in occasional seasons of late rains in the local-
ities mentioned above.

No definite remedy for this trouble has been demonstrated in Cali-
fornia, but spraying with self-boiled lime sulphur just as the fruit is
setting and again with the same following subsequent rains is recom-
mended for trial.

See bulletin 203, page 39, California Experiment Station.

Blossom Rot. Figure 26.

The young fruit decays while still very small and enclosed by the
calyx or outer cup of the blossom. The trouble occurs when wet rainy
weather prevails during the time of fruit setting. It commences in a
rotting of the calyx cup, which is dead and susceptible to decay by
saprophytic fungi, which decay spreads to the young fruit. It is caused
by various fungi, of which perhaps a species of Sclerotinia, apparently
8. libertiana, is most common, causing a decay of the young fruit on the
tree. When such fruit is picked and placed in moist chamber it develops
an abundant cottony mold in which black sclerotia soon forms. This
appears to be the same fungus causing the cottony mold or white rot of

1098

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

the lemon storage. Botrytis vulgaris is also common in this trouble.
Same treatment as brown rot.

Fig. 25. — Brown rot of apricot (Sclerotinia fructigena) .

Spraying for shot-hole fungus might also be of some benefit in this
trouble.

Fkuit Drop. See Almond.

Sour Sap and Seasonal Effects.

The apricot is particularly sensitive to sour sap (see Almond) and
other seasonal effects. It is a tree having a free flow of sap, quick to
respond to stimulating influences and one having the characteristic of
all the stone fruits of forming an abundance of gum when injured in
any manner. On this account, if any active sap movement from the

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1099

Fig. 26. — Apricot calyx rot (Sclerotinia Hbertiana).

roots is started early in the season by warm weather or an abundance of
moisture and this activity be checked again by less stimulating weather
conditions, trouble is very apt to follow. The sap becomes stagnant in
the tissues, full of sugars and other easily fermentable substances, gum
begins to form, sun burn may also occur and very often severe injury
take place in the tissues of the sap wood and cambium layer.

1100

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Crown Gall and Root Rot. See Almond.
Die-Back. See Almond.
Gummosis. See Cherry.

ASPARAGUS.
Rust (Puccinia asparagi). Figures 27 and 28.

Causes premature death of the bushy tops
which grow up after the cutting season, thus
injuring the vitality of the plants. The
fungus causing the rust shows three different
stages, the spring rust, appearing in the
form of elliptical patches on the stems of
plants which are allowed to grow up early
in the season, the summer or red rust, which
covers the tops with a reddish, dusty powder
of spores during the summer, causing their
death, and the black rust stage, which ap-
pears on the tops in the form of numerous
black pustules following the red rust.

During the cutting season allow no wild
asparagus to grow up.

Keep the fields well irrigated and culti-
vated during the summer and fall after cut-
ting stops. Dust the tops thoroughly with
flowers of sulphur about three weeks after

Fig. 27. — Asparagus rust,
winter stage.

Fig. 28. — Asparagus rust, summer stage.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1101

the cutting season ends and repeat this two or three times during the
remainder of the season. .

Select seed for planting from the most rust-resistant plants. See
Bulletins 165 and 172, California Experiment Station.

ASTER.

Yellows.

Characterized by the production of sickly, yellow shoots and abortion

of the flowers. Apparently caused by climatic conditions. Not very

serious in California. No remedy known.

BARLEY.

Closed Smut (Ustilago hordei).

The grain is turned a dark color by
the formation of the fungus spores in its
substance. This remains firm rather
than flying out in a dusty mass, as in the
next form.

Loose Smut (Ustilago nuda). Figure 29.

Differs from the last in that the smutty
substance of the grain scatters out in the
form of black dust, leaving the heads
empty.

Barley is not often affected with smut
in California, so that we can not distin-
guish as to the occurrence of these two
different species. It is advisable, how-
ever, to treat the seed as follows :

Soak for 10 minutes in one of the fol-
lowing solutions :

1. Bluestone 1 pound to 5 gallons of water.

2. Formalin 1 pint to 30 gallons of water.

The seed should be soaked long enough
to get every grain thoroughly wet and
then immediately taken out. If not
planted at once the grain must be dried
before storing. Plant a little more seed
after this treatment than would be used
with untreated grain.

Loose smut alone is more successfully
controlled by the following seed treat-
ment :
in cold water for 5 hours. Then soak in water at a temperature
degrees F. for 15 minutes. The proper temperature must be

Fig. 29. — Loose smut of barley
(Ustilago nuda).

Soak
of 125

5_Bul. 218

1102

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

carefully maintained to make this treatment successful, but it is not
usually necessary in California.

Blade Blight (Helminthosporium gramineum) . Figure 30.

The leaves turn yellow and are covered with elongated black spots.
This is frequently seen in unfavorable seasons when the plants are small
and rather stunted. The plants usually overcome the diseased condi-
tion when weather conditions are favorable.

It is a question whether the primary trouble is not caused by weather
conditions more than by the fungus. In periods of long
continued, cold rain in winter, to which barley is often
subjected, the plants grow very feebly, turn yellow and
form their roots close to the surface of the water-soaked
ground. "When, as sometimes happens, the
seasonal rain suddenly ends and hot, dry
windy weather follows, the surface soil
dries out suddenly, the shallow-rooted bar-
ley is left without moisture and the al-
ready weakened plants fall an easy prey
to fungi.

No remedy feasible or commonly needed.

BEAN.

Mildew (Erj/siphe polygoni).

Produces a white growth of the fungus
covering the surface of the leaves in moist
weather.

Sprinkle with dry sulphur.

Rust (TJromyces appcndiculatus) .

Causes a yellowing and death of the

leaves with the production of a dusty red
rust on the under side. Not usually de-
structive except on plants growing poorly.

,,/

Spot {Collet otrichum lindemuthianum) . Figure 31.

Causes large, scabby, dead spots upon

the pods. Not often serious in this State.

May be controlled by selecting clean seed

Fig. 31. — An-
thracnose of"

Fig. 30. — Blade
blight of bar-
ley (Heimin- and spraying the plants with Bordeaux bean (Coiieto-

thospor ium . trichum linde-

grarmneum). mixture. muthianum).

BEET.
Rust (Uromyces oetm) .

A typical red rust on the leaves, common on sugar and garden beets,
if grown during the rainy season. Not serious.

Bulletin 21S]

CALIFORNIA PLANT DISEASES.

1103

Fig. 32. — Leaf spot on beet {Cercospora beticola).

Leaf Spot (Cercospora beticola). Figure 32.
Produces small dead spots all over the leaves. Quite common in
California, but practically unknown on sugar beets.

Downy Mildew {Peronospora schachtii). Figure 33.
Causes a stunting of the inner leaves and a checking of the growth
of the plant. The fungus is visible to the eye as a mildew on the under

1104

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

side of the affected leaves in the center of the plant. Found recently
in California on sugar beets, this being the first report in this country.
Not yet serious. Occurs only during the rainy season.
When found, the plants should be pulled and destroyed.

Root Rot (Rhizoctonia) .
Appears in young plants as a decay of the main root. Does not
usually kill the plant but causes the root to fork and become misshapen.
Not very serious.

Curly Top — Blight. Figures 34 and 35.
Characterized by thickened, curled leaves, stunted growth, an abun-
dance of fibrous roots and a pronounced blackening of the concentric

Fig. 33. — Downy mildew of beet (Peronospora schachtii).

rings in the interior of the beet. Our most serious sugar beet disease.
The cause of this disease has recently been found to be an insect
( Eutettix) , but its development is very largely influenced by climatic
conditions.

Avoided largely by determining the best time for planting in affected
localities.

See bulletin 184, page 240, California Experiment Station.

Root Knot (Nematode).
Produces small; gall-like swellings on the roots. Has been found in
California but does not seem to have become serious. See page 1076.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1105

Fig. 34. — Curly top of beet.

1106

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Fig. 35. — Curly top of beet. Sections showing blackened fibrovascular rings.

Bulletin 21 S J

CALIFORNIA PLANT DISEASES.

1107

Produces bright
orange masses of
spores all over the
under side of the
Leaves. The fungus
spreads all through
the plant so that it
is not easily con-
trolled.

Cut affected
plants to the
ground and burn.
Spray new growth
with Bordeaux
mixture.

BLACKBERRY.

Rust (Oymnocotiia int ers tit alls ) .

Fig-

Leaf Spot
(Septoria rubi).
ure 36.

Produces small
dead spots on the
leaves. Not usu-
ally very serious.

Spray with Bor-

Fig. 37. — Fruit rot of blackberry
(Botrytis vulgaris).

Fig. 36. — Leaf spot of blackberry {Septoria rubi).

deaux mixture about four
times at short intervals (of
about ten days), the first
application when the buds
are beginning to unfold.

Crown Gall
( Bacterium tumefaciens ) .

Produces large swellings

or galls just below ground.

Destroy affected plants and

use care in planting clean

stock.

Fruit Rot (Botrytis). Fig-
ure 37.

The ripe fruit decays on
the bushes and is covered
with a grey, dusty mold.
Usually not abundant ex-
cept in moist weather.

No treatment feasible.
All affected fruit should be

1108

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

discarded and not mixed with that which is unaffected, as the rot will

spread after picking.

CABBAGE.

Club Foot (Plasmodiophora brassiccc).

Produces large swellings on the roots and stunting or death of the

plants. Not common in California.

Black Rot (Pscndomonas campestris).

This bacterial disease causes the
ruin of the heads, the veins of the
leaves turning black and decay-
ing. The trouble is very uncom-
mon in California if it occurs at all.

CARNATION.

Rust (Uromyces caryophyllinus) .

Produces pustules containing the
reddish, dusty spore masses of the
fungus on the leaves. Not serious
on healthy plants in this State.

Wilt — Stem Rot (Fusarium).
Causes a dry rot of the stem and
root tissue of the plant. Not
serious.

Leaf Spot (Heterosporium echinulatum
and Septoria dianthi). Figure 38.

Produces dead spots on the
leaves. Not important in this
State.

This disease, together with the
rust, may be controlled to some ex-
tent by spraying with Bordeaux
mixture if necessary. In both cases
use care in selecting healthy cut-
tings for propagation and grow
them in fresh soil.

Fig. 38. — Leaf spot of carnation
( Heterosporium echinulatum ) .

CELERY.

Summer Blight (Cercospora apii).
Produces large, irregular dead spots on the leaves during the summer.
Quite common in moist localities but not serious.

Winter Blight (Septoria petroselini, var. apii). Figure 39.
Produces smaller spots than the last, with numerous black pustules
dotting them. Develops more during the rainy season, especially if the
growth of the plants is checked by unfavorable conditions. The disease

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1109

affects mostly the older outside leaves, causing a stunting of the plant
and also decay in shipment.

Spray frequently with Bordeaux mixture at all times during the

Fig. 39. — Winter blight of celery (Septoria petroselini).

growth of the plant, from the seed bed up to maturity, whenever there
is much moisture in the air.

See Bulletin 208, California Experiment Station.

Stem Rot (Sclerotinia).
Causes a reddish, soft decay of the stalks.

Root Rot (Fusarium).

A decay of the roots. Both this and the last occur only when the land

is wet and heavy and the plants growing poorly. Neither is common

nor serious.

CHERRY.

Brown Rot (Sclerotinia fructigena) . See Apricot.

Root Rot. See Almond.

Gummosis.

The cherry, like other stone fruit trees, is very subject to gumming

of the trunk and branches, as a result of any injury. In seasons of

heavy rains during the spring cherry trees frequently show a trouble

1110

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

of this sort quite similar to that of citrus trees. Masses of gum break
out on the trunk and the trees frequently die. Young trees are some-
times affected much like citrus trees, the gum breaking out just at
the surface of the ground. This is a climatic or seasonal effect and
can not be controlled. Trees on wet ground usually show the trouble
worst. This is especially true with young trees which have been planted

too deeply.

Die-Back.

Cherry trees, while not attacked by many fungus diseases in Cali-
fornia, are very subject to injury from unfavorable conditions of soil,
moisture, etc. As a result of such injuries the trees frequently die
back from the top and suffer severely in this way.

This trouble can be controlled only by planting on soil which is partic-
ularly suited to the cherry and by determining the best root stock for
any given type of soil or locality.

Trees in which die-back and gummosis are produced by unusual
climatic conditions should be cut back in the top to sound wood, and
have the trunks protected from sun burn by whitewash or wrapping.

Fruit Drop. See Almond.

CHRYSANTHEMUM.

Rust (Puccinia chrysanthemi) .
Figure 40.

A true red rust causing
injury to the growth of the
plants with the production
of powdery spore masses
on the leaves. Only seri-
ous with us when the plants
do not receive sufficient
water. Vigorously grow-
ing plants which are well
irrigated do not suffer from
this trouble.

CORN.

Smut (Ustilago may Ms).
Produces large, tumor-
like swellings on the ears,
stalks or tassels. These
finally break and discharge
their contents in the form of a black, powdery dust which is chiefly com-
posed of the spores of the fungus. Not seriously abundant.

Fig. 40. — Chrysanthemum rust {Puccinia chry-
santhemi).

"Bulletin 218]

CALIFORNIA PLANT DISEASES.

1111

Rust (Puccinia sorghi).
A powdery, red rust on the leaves. Not serious.

Mold (Diplodia zcw) .
The corn becomes moldy and covered with fungus growth in the ear.
<Quite common in this State on moist land. Affected ears should be

destroyed.

COTTON.
Boll Rot.
The seed and a part of the lint are affected with a soft decay while the
bolls are still green.

Cause unknown. Possibly bacterial. Noticed for the first time in
Imperial Valley in 1910.

Fig. 41. — Nematode galls on cucumber root.

CUCUMBER.

Mildew (Erysiphe cichoracearum) .

A white fungus growth all over the surface of the leaves. Not serious.

Stem Rot (Sclerotinia libertiana).
This dry rot of the stem and root has been found on plants growing
in greenhouses. Not serious except under such circumstances. Use
fresh, unaffected soil.

1112 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Root Knot (Nematode). Figure 41.
Causes swellings all over the main and smaller roots. Found only in
greenhouses. See page 1076.
Control as in Stem Rot.

Leaf Spot (Altcrnaria hrassicw, var. nigresccns) .

This fungus has been known to do considerable damage in a few cases,
causing large dead spots, later covered with the black fruiting fungus.
Not important as yet.
Can be controlled with Bordeaux mixture.

CURRANT.

Mildew (Sphaerothcca mors-uvw) .
A white, powdery mildew on the leaves and fruit.
Dust with dry sulphur while the leaves are wet with dew, if treatment
seems necessary.

DAHLIA.

Mildew.

A white, powdery mildew on the leaves. Not serious.
Treatment as for currant mildew.

DEWBERRY. See Blackberry.

Fig. 42. — Fruit rot of egg plant (Botrytis vulgaris).

EGG PLANT.

Rot (Botrytis). Figure 42.

A moldy decay of the fruit. The fungus mentioned has a grey,
dusty appearance. Not serious.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1113

Wilt — Stem Rot (Nectria ipomocw).
This fungus causes a dry rot of the stem and root. Usually occurs
only on old plants in which the stem has been injured.
Do not plant in affected soil if the trouble is serious.

EUCALYPTUS.
Damping Off.

Causes great losses by a stem rot and dying of the young plants in
the seed bed.

Sow the seed in clear sand, transplanting to better soil as soon as the
seedlings are large enough to handle. Keep as dry as possible without
checking the growth seriously.

Fig. 43. — Crown gall of eucalyptus.

Water only in the morning and as little as possible on cloudy days.

Mildew.
A powdery mildew has been known to occur on seedlings, but is not
of general occurrence.

Treat with dry sulphur as for other mildews, after destroying badly
affected plants. Observe precautions as for damping off with regard
to water.

Leaf Spot (Hcndersonia sp.).
Sometimes seen on the blue gum (Eu. globulus), causing dead spots
on the leaves. Not serious.

1114

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Crown Gall. Figure 43.
The seedlings of some species frequently develop gall-like swellings
on the stem near the surface of the ground. This condition does not
seem to be particularly injurious. Cause unknown. Possibly a normal
condition. GRApE

Mildew (Uncinula spiralis). Figure 44.

A white powdery mildew on the leaves and fruit clusters.
Dust thoroughly with flowers of sulphur in moist weather before the
fungus develops extensively. See Bulletin 186, California Experiment

Fig. 44. — Powdery mildew of grape (Uncinula spiralis).

Station. On account of the importance of this disease, we quote as
follows from California Experiment Station Bulletin 197 :

' ' The most common mistake of those who have attempted to follow the
directions of the bulletin (186) has been a failure to treat the vines
thoroughly or rapidly enough in the beginning of the season. It can
not be too strongly urged that the most effective way to control the
mildew is by a thorough and effective sulfuring in the beginning of the
season. This alone will in most parts of the State keep the vines free,.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1115

and the sulfuring during the blossoming is needed only for its effect on
the setting of the fruit, and as an extra precaution. Sulfuring later, if
needed, is a proof that the first
two have not been well done.
This is true for the whole of
the two central valleys and
for most of California, except
the coast belt subject to sum-
mer ocean fog.

"Definition of a Thorough
and Effective First Sulfuring.
— The first sulfuring should
be made when the shoots are
between 6 and 15 inches long.
It should be done in such a
way that every part of every
leaf of every vine in all parts
of the vineyard receives some
sulfur, and the whole vine-
yard should be gone over in
as short a time as possible.
This will be a thorough sul-
furing. To be effective, it
must be followed immediately
by two or three days of warm
weather. Unless this happens,
the sulfuring should be re-
peated as many times as are
necessary until the proper
weather conditions are ob-
tained. ' '

Black Knot. Figure 45.
(California Experiment
Station Bulletin 197) : "This
is one of the commonest and
most widely distributed dis-
eases of the vine in California.
Many specimens are received by the Experiment Station every year,
from nearly all vine-growing sections. It consists of peculiar growths,
or swellings, usually near the surface of the ground on the upper parts
of the roots or the lower part of the trunk. It often occurs, also, on all
parts of the trunk and branches, but only rarely on the canes.

'As a rule it does little damage unless it occurs on young vines, or
attacks old vines very severely. Figure 45 is a photograph of a young

Pig. 45.

-Black knot of grape (Bacterium
tumefaciens) .

1116

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

vine very badly attacked, showing a large mass of knots at the surface
of the ground, and four on the stem above the surface. Such a vine is
almost girdled and could never develop into a healthy plant. In some
cases where the knots occur on a branch or arm they could be removed
and the vine might recover perfectly.

"It is not uncommon to find vines with large masses of knots on all
sides of the trunk and on all the arms, which yet make a vigorous
growth and produce good crops. When the knots extend all around

the trunk of an old vine,
however, it may be girdled,
and, while it seldom dies, it
may become weak and worth-
less.

' ' Various theories have
been advanced as to the
cause of this disease, but the
most commonly accepted is
that it is due to abrupt
changes of temperature, and
especially to autumn frost
occurring before the vine
has become thoroughly dor-
mant. This cause alone,
however, does not seem to be
sufficient to cause the dis-
ease. The knots appear only
on vines growing in moist
places, and especially in
sandy soil in the hotter re-

gions

#

' ' Anything which causes
a vine to grow vigorously
late in the season and pre-
vents the proper ripening of
the wood, renders it suscep-
tible to the disease.

' ' In accordance with these
ideas, the remedies advo-
cated aim at causing the vine
to ripen its wood early and
fig. 46.— couiure disease of the vine. completely. These remedies

are drainage of the soil, fertilization with phosphatic manures, longer
pruning, raising the trunk of the vine, and removal of the knots. Swab-
bing with lime, sulfate of iron, and other antiseptics has proven useless. ' '

*It is now known to be due to an infection by the crown gall organism, Bacterium
tumefaciens.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1117

COULURE OF MUSCATS. Figure 46.

(California Experiment Station Bulletin 197): "The Muscat of
Alexandria, from which the bulk of our raisins is made, has a tendency
to drop its blossoms without setting. This trouble is usually known in
California by the French term of 'coulure,' which may be translated
'dropping.' The first crop is particularly subject to this defect, which
is often so serious that a large part and sometimes the whole of the first
crop is lost."

This trouble is due to a failure of pollination of the blossom. The
author recommends as a remedy planting occasional rows of other
varieties with the Muscat. For this purpose the Palomino, Perruno,
Beba and Berger are suggested.

MISCELLANEOUS DISEASES.

The grape is affected in California by several miscellaneous and
peculiar diseases, most of which are not very clearly defined. Some of
these have received the names Anaheim Disease, Red Leaf, Little Leaf
and other local names.

The first named, also called the California Vine Disease, was of the
greatest importance a number of years ago when almost all the vine-
yards in southern California died from a mysterious trouble which
received this name. Although carefully investigated at the time by
Professor Newton B. Pierce, at that time of the United States Depart-
ment of Agriculture, no definite cause of this disease was ever discovered.
At present vines are occasionally affected with something which might
pass for the same disease, but it is difficult or impossible even for the
experienced plant pathologist, save, perhaps, one who was familiar with
the Anaheim disease at the time of its first and greatest period of preva-
lence, to say just what is really Anaheim disease and what is one of the
various troubles which have received other names. So little is under-
stood about these vine diseases at present that it is scarely worth while
to attempt to discuss them in a publication of this sort. We quote as
follows from California Experiment Station bulletin 197:

Mysterious Dying of Vines (Anaheim Disease). — The vine, like most plants,
especially fruit trees, which are cultivated on a large scale, is subject to diseases of
more or less intensity whose cause is not thoroughly understood. These diseases are
(1) caused by parasitic organisms which have so far escaped detection, or (2) what
is usually known as "physiological."

Physiological diseases are presumably due to some unfavorable conditions. For
example, chlorosis, or the failure of the leaves to develop chlorophyll properly, is due
to an excess of soluble lime carbonate in the soil, and is intensified by cold, dampness
and the susceptibility of the variety.

The most serious of these two classes of diseases, which affects the vines, is the
Anaheim, or, as it is sometimes called, the California Vine Disease. Notwithstand-
ing that it has been the subject of continuous investigation for over fifteen years its
cause is still quite obscure. Even the characterization and detection of the disease
are so uncertain that vineyards, which after several years of observation by the most

6_Bul. 218

1118 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

experienced investigators have been pronounced infected, have later been declared
free. This has led to such a diversity of opinion that while one expert claims that
the disease exists in every vineyard in the State, another would have us believe that
no such disease exists at all, and that all cases of dying vines can be ascribed to one
or other of the recognized vine diseases.

Neither of these extreme views seems to explain completely the observed facts.
While many cases of supposed Anaheim have proved to be nothing but Phylloxera,
root-rot, vine-hopper, drought, etc., there still remain a large number of unexplained
cases.

In some cases the symptoms are practically identical with those of some of the
"physiological" diseases which affect the vine in Europe. Typical cases of Rougeot
have been noted in Contra Costa County, of Brunissurc in San Joaquin, and of
Folletage in Fresno, Kings, and other counties. In Sonoma County the disease of
Red-leaf, which has some analogy with Anaheim, has been studied by Mr. O. Butler.
An account of these diseases may be found in Bulletin 168, entitled "Observations
on Some Vine Diseases in Sonoma County."

In a general way, as these troubles are due to soil and climatic conditions which
weaken the vine, they are to be combated by cultural methods which tend to invigor-
ate. Shorter pruning, thorough cultivation, irrigation or drainage, and fertilization
will in most cases be effective in curing vines which are not too far gone.

Many cases have been brought to the attention of the station during the last two
years, in which vines which were apparently healthy the previous year have failed
to bud out in the spring, or budded out weakly and very late. The cause, in most
cases, seemed to be some injury to the vines during the growing season of the pre-
vious year. This cause was in many cases the attacks of vine-hoppers. Black
Prince vines growing in Tokay vineyards have very often been killed. This seems
to be because the vine-hoppers, having a special fondness for this variety, congre-
gate in large numbers on such isolated vines. Whenever the hoppers are sufficiently
abundant to cause the dropping of the leaves in summer, the vine fails to ripen its
wood properly. Without mature green leaves the buds and canes do not receive the
stores of starch which they need for the new growth in spring, and will either grow
poorly the following year or fail to start at all.

When a new growth of leaves in autumn follows summer defoliation by hoppers,
mildew, or other causes, the effect is even worse. The new shoots which start
exhaust what food reserves the vine possesses, and the leaves are killed by the early
winter frosts before they have been able to return the supplies they have taken from
the canes. Similar, but less severe, effects have been observed following a bad attack
of mildew.

This starvation of the canes and buds may be brought about in another way,
namely, by the production of too large a crop. It is often possible, by excessively
long pruning, to cause a vine to produce an abnormally large crop of grapes. The
larger the crop the more material it takes from the vine, and if too large, the vine
is unable to support it and at the same time lay up reserve materials in its canes
and buds. In consequence, an extra large crop is often followed by weak growth
in the spring, and a consequent small crop the following autumn. Vines of heavy
bearing varieties may even be killed in this way, by repeated long pruning.

This fact has been long recognized by practical grape-growers. Lately, Professor
L. Ravaz,* of the National School of Agriculture at Montpellier, France, has
advanced the opinion that the death of vines, as a consequence of overbearing, is
much commoner than is usually supposed. This overbearing may occur as a conse-
quence of various conditions other than long pruning. Some seasons are peculiarly
favorable to heavy crops. Certain diseases and injuries induce temporary heavy
bearing. Whatever the cause of abnormally heavy crops, Professor Ravaz believes
that they may result in the death of vines. This is the explanation he gives of the
death of large numbers of vines in southern France, Algeria, and other countries,
and he ascribes our so-called Anaheim disease to the same cause.

This is substantially the explanation given of the dying of vines in Santa Clara,

* "Influence de la surproduction sur la Vegetation de la Vigne," by L. Ravaz, Coulet
et fils, Montpellier, 1906.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1119

in Bulletin 134, which was published before the region was declared infested by
Anaheim disease. Whether this explanation is sufficient is still doubtful, though
it is rendered probable by the fact that healthy young vineyards are now growing
in Santa Clara, on the same soil where vines have been killed by Anaheim disease.

GRAPE FRUIT. See Orange.
GUAVA.

RUSSETING.

In this trouble the surface of the fruit shows a scabby condition indi-
cated by the above name. Thought to be caused by an insect.

Fig 47. — Rust of hollyhock (Puccinia malv ace arum) .

HOLLYHOCK.
Rust {Puccinia malvacearum) . Figure 47.
In this disease the fungus injures the leaves seriously, becoming visible
in the form of numerous small pustules of spores on the under side.
These pustules are dense and compact rather than dusty as in most rusts.
The wild mallows are affected with the same fungus. Hollyhocks grown
in rich soil with an abundance of water are much less affected than those
which lack moisture.

1120

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Fig. 48. — Leaf spot of iris (Hetero-
sporium gracile).

Irrigating and fertilizing abundantly will control this disease.
Spraying with Bordeaux mixture and other fungicides is sometimes
resorted to, but this treatment is not very satisfactory.

IRIS.

Leaf Spot (Ilctcrosporium gracile). Figure 48.

Large, elliptical dead spots appear
on the leaves, with a yellow margin
between the dead and the green tissue.

Quite disfiguring, but no treatment
ordinarily considered necessary.

LEMON.

Gummosis. Figure 49.

Characterized by the exudation of
gum from the trunk of the tree just
above the point of budding. The tree
appears yellow and dies when badly
affected. Occurs on poorly drained,
heavy soil, especially if the point of
budding is deeply covered with earth
and where the soil about the trunk
is undisturbed by cultivation. This
trouble is more common on lemons than on oranges.

Gumming is a characteristic of the citrus tree when affected by any
injurious condition. Frequently, for instance, when trees have been
extremely dry and suffering from a lack of moisture gum will break out
at the crotches or twig axils when an abundant supply of water is
furnished. If the twigs in this or any other manner are caused to die
back for a short distance gum is very likely to exude after irrigation
at the point where the dead portions of the twig join the live tissue.
Any injury or irritation may have the same effect. When citrus trees
are budded, either in the nursery or in the case of orchard trees, gum-
ming often occurs at the point of budding, particularly if a large supply
of moisture is furnished soon after the budding is done. Many buds
are often killed in this way as a result of rain or irrigation. Such effects
as these are not usually very serious, except that in the case of budding
the process may have to be repeated.

Orange or lemon nursery trees one or two years of age sometimes gum
badly just above the point of budding from no very apparent cause. As
a result of such gumming the cambium layer is killed and if the injury
is extensive the tree may die. In the majority of cases, however, if the
trees are affected on only one side and planted and cared for properly,
they make a complete recovery and after a year or two the injury disap-

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1121

pears. These cases probably start in the majority of instances from an
excessive flooding of the soil with water, put on either while the trees
are growing to force them along or just before they are dug in order
to assist the operation of " balling." Trees affected in this way when
received for planting should not be looked upon as having any serious
contagious disease, but the buyer should simply discard those in which

Fig. 49. — Gum disease of lemon.

the inner bark is badly affected and notify the nurseryman of the num-
ber of trees found in this condition. If the trees have once been planted
and then die or fail to grow it is impossible to decide whether the gum-
ming took place before or after the trees were planted.

In order to successfully control gum disease in orchard trees, soil con-
ditions must first of all be improved by securing drainage, removing

1122 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

soil from about the bud and thoroughly cultivating or digging about
the tree. Water must not be allowed to stand about the trunk or the soil
remain continually saturated. After thus improving conditions, the tree
itself may be treated by taking out narrow slits of bark on several sides
of the trunk, extending from the ground up to the fork. These slits
should pass through the gummy portion and also the unaffected bark.
This will usually suffice to effect a cure if taken in time and if soil con-
ditions are sufficiently improved.
For further treatment see Bulletin 200, California Experiment Station.

Brown Rot (Pythiacystis citrophthora) . Figure 50.
A very virulent form of decay spreading rapidly through the boxes
from fruit to fruit. Affected specimens show a brown, rather dry decay

Fig. 50. — Brown rot of lemon (Pythiacystis citrophthora).

of the rind upon which a delicate, scanty white mold develops when
considerable moisture is present. Fruit out in the open shows no mold
on the surface. Affected fruit has a peculiar odor which is very char-
acteristic. Mostly seen in lemons held in storage for curing. In wet
weather this decay often appears on the fruit while still on the tree, but
it is mostly confined to that within two feet of the ground. The disease
affects all kinds of citrus fruit in this manner.

The fungus which causes this trouble is primarily a soil inhabitant,
living naturally in the ground beneath the trees where its spores are
produced.

Orchard infection is prevented by keeping the trees pruned up some-
what from the ground, cultivating the soil under the trees in summer
and covering it in winter with straw or a green cover crop. Spraying
the ground under the trees in winter with thick Bordeaux mixture is
also helpful. The worst infection, that of lemons in storage, is con-

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1123

tracted in the tank of the washing machine where the water becomes
extremely infectious from the presence of spores brought in with the
orchard soil and dust. This is easily controlled by disinfection of the
wash water with copper sulphate.

See Bulletin 190, California Experiment Station.

Cottony Mold — White Rot (Sclerotinia libertiana). Figure 51.
Causes decay of the fruit in the curing house with the production of
an abundant white mold spreading over the lemons. In this mold

Fig. 51. — Cottony mold of lemon {Sclerotinia libertiana).

are found irregularly-shaped, black, seed-like bodies called sclerotia
from which another stage of the fungus develops. The same fungus
also develops in the orchard soil during the rainy season and often
becomes very abundant upon green-manure crops or other vegetation
growing about the lemon trees, particularly upon the vetch. The
sclerotia develop upon green-manure crops or directly upon the soil,
the latter during the rainy season, and out of them grow little funnel-
shaped toadstool-like bodies which give off the spores of the fungus.

1124

UNIVERSITY OP CALIFORNIA EXPERIMENT STATION.

The fungus is not actively parasitic and it has been found difficult
to infect lemons with its spores save when they are injured or bruised
in some way. They also require considerable moisture for infection.
Experiments have shown that almost all the infection takes place at
the stem end of the lemon where it is cut from the tree, and practically
all, it is probable, in the washing water, except in the case of fruit
allowed to stand out in the rain for some time, when infection may take
place.

Cottony mold sometimes develops to a considerable extent in packing
houses where the fruit is being washed in bluestone solution to prevent
brown rot, from which fact it appears that a strength of this substance

which kills brown rot
spores does not kill those
of the cottony fungus.
Laboratory tests have
shown this to be a fact.
The control of cottony rot,
therefore, depends upon
either using the germicide
stronger than that used
for brown rot or finding
means for preventing the
development of the fun-
gus in the orchard. Along
the former line we may
say that it is not safe to
use bluestone in the wash
water much stronger than
it is now being used in
many houses for brown rot control ; a strength of 1/50 of one per cent,
or about 1J pounds of bluestone to 1,000 gallons of water. This would
mean putting in about the quantity of bluestone stated into a 1,000-
gallon tank in the morning and fortifying this with about one pound
more in the afternoon, after considerable wash water has entered the
tank. The question of the strength of bluestone in lemon wash water
depends to a large extent upon the quality of the water used as to its
alkali content, since the alkali salts neutralize the copper sulphate.
This whole question of disinfecting lemon wash water is now being
investigated at the Whittier Laboratory.

In regard to orchard control of this trouble, we may say that the cot-
tony mold has had a very marked prevalence since the use of vetch as
an orchard cover crop became so general. There is much ground for
believing that these facts are related to one another, cottony mold

Fig. 52. — Peziza developing from sclerotium of
cottony mold fungus (Sclerotinia libertiana).

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1125

having become more abundant on account of the opportunity given for
its development in the orchard by the presence of the vetch plant, upon
which it develops particularly well. We are by no means ready to
advocate the discontinuance of cover crop practice in lemon groves for
this one reason, although it may be said that other factors are develop-
ing in actual practice which make the growth of such a crop in a lemon

Pig. 53. — Peziza of cottony mold fungus growing in orchard soil.

grove undesirable from some other point of view. This whole subject
is now under investigation and will be reported on in a future bulletin.
See Bulletin 190, California Experiment Station.

Gray Mold {Botrytis vulgaris).

This produces a dark colored decay of the rind on which a dirty gray
mold develops. The fungus is able to develop at low temperatures close
to the freezing point and sometimes causes considerable loss in fruit held
in cold storage. Not ordinarily very serious.

1126

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Blue and Green Mold (Penicillium italicum and P. digitatum). See Orange.

Twig Blight (Sclerotinia .lioertiana) .

The twigs die back from the tip in moist weather, showing to some
extent a white moldy fungus upon the surface in which may be imbedded
small, hard, seed-like bodies or sclerotia, at first white but finally becom-

Fig. 54. — Green and blue mold rot of lemon (Penicillium digitatum and italicum).

ing black. A mass of gum exudes at this point. This fungus, which is
the same as that causing the cottony mold, occasionally infects the tree
itself, both with lemons and other citrus trees, with the effect just

Fig. 55. — Supposed effect of wither-tip fungus on lemon fruit (Colletotrichum

gloeosporioides) .

described. The infection comes from spores produced by the growth of
the fungus upon the green manure crop. Not serious. This effect is
sometimes confused with that of the next described disease.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1127

Wither-Tip, "Tear Stain" (Colletotrichum gloeosporioides) . Figures 55 and 56.

The effects of this disease consist in a general way in a spotting of the
fruit and leaves and killing back of the twigs, and an attack upon the
young, newly-formed fruit, causing it to drop. To what extent, how-
ever, such effects occur in California solely from the attacks of this
fungus, without the aid of other harmful conditions, is somewhat doubt-
ful and difficult to determine. Wither-tip is a trouble of quite common
occurrence in Florida and probably most other citrus growing regions.
It has been known to exist in California for some time but there has
always been a question as to how much this fungus is really parasitic
and how much it develops simply in a secondary manner upon tissues
injured in other ways. Little attention was given to the subject in
California until the winter of 1908-09, when there appeared to be a
considerable epidemic of wither-tip in southern California, particularly
on lemons and grape fruit. Since that time the subject has received
considerable investigation.

The most pronounced effect upon lemons attributed to the wither-tip
fungus has been a slight spotting of the fruit, the spots being quite
numerous upon the exposed side of the lemons while still on the tree,
each spot of small size and reddish color. Such spotting has been quite
generally attributed to this fungus and yet it may be said that in
numerous efforts made to produce such an effect by direct infection
with the spores of the wither-tip fungus, entire failure has always been
the result. The same is true in regard to the dropping of young fruit.
It has frequently been assumed that this is an effect of the wither-tip
fungus, yet efforts made to produce the same effect by spraying young
lemons profusely with wither-tip spores have always failed to produce
infection or cause such fruit to drop any more than that which was not
sprayed.

The fungus commonly shows itself to the eye in the form of numerous
minute black dots upon the surface of dead twig tips or on dead spots
on the leaf. In the latter case, starting on spots killed by fumigation,
fire or other injuries, or possibly without preliminary injury on old,
nearly dead leaves, the spots slowly spread in an oval form, with a yellow
band between the dead and green tissue and the characteristic black dots
(pycnidia) upon the surface of the dead portion.

Another fungus, a species of Pleospora, having a similar appearance
and effect, has also been found quite abundantly on citrus trees in the
northern part of the State.

The wither-tip fungus is one of the commonest inhabitants of our
citrus trees. Every dead twig, every fallen leaf, every leaf or twig
injured by fire or any other cause, immediately becomes covered with a
flourishing growth of this fungus. Young lemons which fall to the
ground from any cause show the same fungus upon them after a short

1128

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

time. It has even been found that the most healthy, green leaves, if
picked from the tree and placed in a moist chamber, soon become cov-
ered with this wither-tip fungus. Trees suffering from gum disease,
gophers, drouth or any other influence which causes them to lose their
vitality and begin to weaken and die back in the branches soon develop
an abundance of this organism. It is also likely that citrus insects,
like the red spider and any other which punctures or injures the fruit,
may promote the development of this fungus.

All in all, our conclusion has been that it is extremely doubtful
whether the wither-tip fungus ever in California attacks sound, unin-

Fig. 56. — Effect of wither-tip fungus on sickly lemon leaf and twig (Col-

letotrichum gloeosporioides) .

jured, vigorous foliage, twigs or fruit, or develops at all, save in a
secondary manner or following some other injury. The subject is still
receiving careful investigation and will be made the subject of a future
bulletin.

"Within the last two or three years considerable spraying has been
done in lemon groves in southern California with the idea of combating
the supposed effects of this fungus. Such work has been done with
Bordeaux mixture and also with various sulphur sprays made by com-
bining sulphur with lime, soda or potash. Some growers have believed
that they saw good results following such spraying, while others were
unable to see such benefits. "We are following the results of such work.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1129

Red Rot. Figure 57.

A curing-house trouble in which the rind develops a rusty bronze color
and gradually dries down into a sunken condition with a dark red or
black color.

Cause unknown; apparently not a parasite.

Fig. 57. — Red rot of lemon.

Fig. 58. — Peteca of lemon.

Peteca. Figure 58.

This trouble shows itself in the form of deep sunken pits in the rind

of the lemon after it has been in the curing house for some time. The

tissue at these spots is found to be dried and shrunken prematurely.

1130

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

The trouble is not serious, save in its effect upon the appearance of the
fruit. Cause unknown.

LETTUCE.

Damping Off (Botrytis vulgaris).
Drop (Sclcrotinia libertiana) .

The plants wilt and die, collapsing upon the ground. The stem rots
off just at the surface of the ground and one or the other of the above
named fungi is usually found at this point. Other damping off fungi
may cause the trouble in some instances.

See Tomato.

LOGANBERRY. See Blackberry.

Fig. 59. — Scab of loquat (Fusicladium eriobotryae) .

LOQUAT.
Scab (Fusicladium eriobotryce). Figure 59.

Similar to apple and pear scab, to which trees this is related. Affects
both fruit and leaves.

Blight (Bacillus amylovorus) .

The blossoms and twigs wither and die. This trouble is caused by the
pear blight organism, to which the loquat is quite susceptible.
Same treatment as for pear blight.

MADRONE.

Leaf Spot (Sphaerella arbuticola)

Produces disfiguring dead spots on the leaves.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1131

NURSERY STOCK.
Crown Gall. Figure 11.
Very common on the roots of nursery trees, particularly those of the
stone fruits. See Almond.

Discard affected trees and never use such for planting. Do not grow
nursery stock on affected land.

Root Knot {Nematode). Figure 41.
These microscopic worms sometimes invade the nursery, producing
galls and swellings all over the roots of the young trees.
Destroy affected plants.

Allow infested soil to dry for a season before using it again.
See page 1076.

OAT.
Rust ( Puccinia graminis ) .

Produces numerous pustules of the black or red rust condition on the
surface of the plants, sometimes covering the leaves with the reddish,
powdery spores. Sometimes abundant in wet seasons, badly injuring
the crop.

No treatment is feasible save the use of resistant varieties.

Smut (Ustilago avenw).

Causes the heads of grain to turn into black, dusty, smutty masses.
May be entirely pre-
vented by the seed
treatment recom-
mended for barley
smut.

OLEANDER.
Twig Gall.
( Tuberculosis ) . Fig-
ure 60.

This plant is some-
times affected with
galls or swellings on
the stems and twigs,
very similar to the
olive disease of the
same nature. Ap-
pears to be caused by
the same or a very
similar organism. Not
serious.

Fig. 60. — Stem gall of oleander.

Leaf Spot (Macrosporium nerium).
Produces dead spots on the leaves. Not important.

1132

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

OLIVE.

Tuberculosis (Bacterium Savastanoi). Figure Gl.

This is a bacterial disease, the parasitic organism causing a production

•of galls of considerable size on the trunk, branches and small twigs.

Some varieties are more susceptible than others. If taken in time the

Fig. 61. — Tuberculosis of olive (Bacterium Savastanoi).

disease can be successfully controlled by cutting out all affected parts
and saturating the wounds with a strong disinfectant.
See Bulletin 120, California Experiment Station.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1133

Leaf Spot (Cycloconium oleaginum)
Causes spots of considerable size on

the leaves. No treatment is usually

necessary. Dry Rqt Figure 62.

Characterized by the appearance of

numerous large spots on the fruit which

dry and sink in. During some seasons

the olive is considerably affected with

this trouble. Cause not known.

Root Rot (Toadstool disease). See Almond.

ONION.
Downy Mildew (Peronospora schleideniana).

Causes serious losses some years in
onions grown for seed during the win-
ter. The fungus affects the seed stalks
and leaves with the production of large
dead areas upon which may be seen the
dark, purplish-colored mildew. The seed
stalks topple over and fail to develop
seed.

This disease has not been successfully
controlled in California, but in Eastern
states has yielded fairly well to spray-
ing with Bordeaux mixture, to which a
resin "sticker" has been added. This
spraying must be done at frequent in-
tervals, commencing before the mildew
appears.

The development of resistant strains
by seed selection is promising.

Fig. 62. — Dry rot of olive fruit.

ORANGE.
In the consideration of diseases of the orange and other citrus trees,
it is desirable to mention at the outset certain peculiar characteristics of
such trees which distinguish them to a considerable extent from any
other cultivated plant. These features make the citrus tree specially
liable to peculiar, obscure effects of climate, soil or other non-parasitic
conditions, and in making an investigation of citrus diseases one should
not fail to keep these peculiarities of the citrus tree prominently in
mind. First, is the very free circulation of water from the roots up into
the tops, which occurs when plenty of moisture is available in the soil.
This water carries with it all the food materials from the soil which the
tree takes up and thus we see that the citrus tree must take up large
7_Bul. 218

1134 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

amounts of such food material very freely when large amounts of soil
moisture are available. This feature is of no special importance when
the trees receive a uniformly sufficient supply of water, but must have
very decided effects when the moisture supply is irregular and the soil
becomes alternately ..very wet and very dry. In such cases the soil food
materials are supplied to the tree in a correspondingly irregular manner.

Connected with this feature is the second peculiarity which we would
mention, namely, the quickness with which citrus trees respond when
needed water is supplied. Trees which are suffering from dryness, and
from no other cause, show a most marvelous sending forth of new shoots
and rapidity of growth when water is applied to the roots. Inversely,
the trees are as quick to suffer from a lack of moisture as to respond to
an addition of it. Their tendency is to form a large amount of new,
succulent tender growth, both in the top and root, when water is sup-
plied and the distress of the tree is proportionately greater if a shortage
of water follows, on account of the presence of this growth.

Again, the tree is peculiar in being ready to grow at any time of year,
particularly if its growth has been checked somewhat by lack of moisture.
It has almost no reaction to seasonal conditions. Normally, however,
the tree has three or four fairly well-defined periods of growth during
the year, being intermediate in habit between deciduous trees, which
have one growing and one resting period, and most evergreen tropical
trees which grow more or less continuously all the time.

Still further, a feature of great importance is the tendency of the
citrus tree when injured in any way, either mechanically or physiologic-
ally, to produce a quantity of gummy substance which may run out at
the wounds or break out through the bark. The formation and presence
of such gum, when once started, may become a chronic source of irrita-
tion to the tissues after the cause of the original injury has entirely dis-
appeared, and furthermore, the gum is often a source of trouble through
the secondary fermentation or decay which it may undergo in the tissues
of the plant.

It is the tendency in most citrus species, and particularly in the
varieties most commonly cultivated, to produce fruit asexually, ap-
parently by purely vegetative growth without the process of pollination.
In the Washington navel orange, for instance, and probably to a greater
or less extent in other citrus fruits which are seedless or nearly so, the
fruit appears to be simply a vegetative growth like the leaves, rather
than a product of sexual fertilization. If this be true, it is evident that
herein exists a most important difference, from a practical as well as
investigational standpoint, between the citrus and most other cultivated
fruits.

All these peculiarities are of great significance in any investigation

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1135

concerning the citrus tree, and make, in California at least, the con-
sideration of plant physiology, soil and climatic conditions, and other
similar factors of more importance than the study of parasitic attacks.

Gummosis. See Lemon. Figure 49.
Scaly Bark. Figure 63.

Characterized by the appearance of scaly areas of bark on the trunk
or branches, the outer bark rising in scales from the inner. Small drops

Fig. 63. — Scaly bark of orange.

of gum exude in spots on the affected portion, which gradually spreads.
Affected limbs die back slowly but new growth keeps taking their place
and the tree lives for many years in an unhealthy condition.

This trouble apparently originates in an irregular moisture condition
of the soil. Practically all the affected trees in the State have been in

1136 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

their present condition for many years and seem to have become affected
at a time when irrigation by flooding was generally practiced and culti-
vation received little attention.

The worst affected trees can not be saved, but should be dug out and
replaced. Trees where the disease exists only on the branches will
recover if affected parts are cut off. In case the scaly bark is on the
trunk and the patch is not too large the diseased portion should be cut
out to healthy bark and the wound painted over. Such cases will almost
invariably heal completely.

If the trunk is badly affected, but the tree in fairly good condition,
the scaly surface bark should be scraped off and several slits cut through
the affected area. The scaly part may then be painted over with pure
neatsfoot oil, linseed oil, 10 per cent caustic soda or potash solution, or
kerosene oil.*

The soil about the tree should be thoroughly dug up and the applica-
tion of oil or whatever is used repeated about once a month for several
months. This disease, as well as the last, is not contagious and no infec-
tion need be feared to neighboring trees.

See Bulletin 200, California Experiment Station.

Mal di gomma.

A virulent decay of the bark of the roots from the surface of the
ground downward. This is occasionally found on trees in extremely
heavy, wet soil or where too much water is used close about the trunk
of the tree.

Affected trees can rarely be saved but may be replaced successfully if
soil conditions can be improved.

See Bulletin 200, California Experiment Station.

Exanthema — Florida Die-Back.

The branches die back from the ends and numerous axillary buds
develop, forming bushy tufts of small twigs all through the top of the
tree. Corky outgrowths develop on the bark of the twigs and gum
exudes from these places. In the first stages of the disease there develop
near the center of the tree abnormally large, dark green leaves, giving
the tree a false appearance of unusual thrift. The fruit takes on a pale
yellow color while still small and immature and has an insipid sweetness
with no development of acid quality. Dark brown spots or patches
appear on the rind and from these as centers the oranges crack and split.

This disease occurs in California mostly upon coarse or gravelly soils
or subsoils, following the application of stable manure or other nitrog-
enous material in an organic form. It is most apt to occur when such
fertilization is practiced on trees which have not previously been receiv-

* Injury is sometimes caused by a too abundant use of these substances, especially
on badly affected trees.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1137

ing it, especially if they have been suffering somewhat from lack of plant
food and water. The disease may be likened to a form of indigestion.

On these soils citrus trees should receive very careful irrigation to the
end that the ground may be kept continuously moist and not be allowed
to become alternately wet and dry, as is the tendency on such porous
soils. Fertilization should be uniform without the sudden application
of large amounts of manure or organic fertilizers.

See Bulletin 200, California Experiment Station.

Chlorosis.
This term applies to cases where the leaves become yellow and pale,
lacking the normal green
color. No definite dis-
ease is indicated by these
symptoms, more than
that the trees are in dis-
tress of some sort. The
cause of the trouble is
usually to be found in
some unfavorable soil
condition.

Mottled Leaf. Figure ('A.
What has been said in
the last case applies to
this also. Affected trees
show a yellowing of the
leaves between the veins,
with the green color
only along the mid rib
and the lateral veins,
giving the leaf a mottled
appearance. Examina-
tion shows that leaves
once green never become
typically mottled there-
after, although they may become lighter in color or even bright yellow.
Typical mottled leaves are found only toward the ends of the shoots and
represent leaves in which the green color has never completely de-
veloped, rather than those in which the chlorophyll has once existed
but then disappeared. Mottled leaf is a case of non-development or
slow development of chlorophyll. Along with the mottling of the
leaves there also occurs, if the trees are badly affected, a decided short-
age in the amount of fruit and in typically bad cases the fruit present

Fig. 64. — Mottled leaf of orange.

1138 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

is of very small size, becoming fully colored when only an inch or two
in diameter. Considerable die-back also occurs and the foliage is thin
and weak, giving the tree a brushy look, with many small, dead twigs at
the extremities.

Mottled leaf is by no means to be always regarded as a symptom of
disease or a cause for alarm. Frequently in the winter young, rapidly-
growing trees show such a condition in their youngest leaves, especially
during periods of long continued cold rain. This is to be regarded as
simply a temporary set-back in the development of the leaves and with
warm weather the normal green color appears and the leaves soon put
on their natural appearance.

A more serious condition of mottled leaf may result from any one of
a variety of causes. It does not necessarily indicate any specific disease.
There has been, however, in southern California, particularly during the
past year, quite a widespread condition of this sort, which appears to be
of the same general nature. This condition has been attributed to a
variety of causes, most of which probably had nothing whatever to do
with the disease. One theory that has been given prominence is that
mottled leaf is due to the presence in the soil of an excess of magnesium
over lime. Not long previously the opposite theory was held in a similar
case in the San Joaquin Valley, namely, that mottled leaf is due to an
excess of lime in the soil.*

Examination of typical cases of mottled leaf all over the affected dis-
tricts shows the following facts to be true : The trouble is less generally
abundant near the coast and more abundant inland. Oranges are more
affected than lemons, and Valencia oranges more than Washington
Navels. Oranges top- worked on other citrus trees are worse affected
than those which were budded in the nursery. Oranges top-worked on
lemon trees are rather worse than those top-worked on orange trees.
(The worst combination in this respect is, therefore, Valencia top-
worked on lemon.) Trees are worse affected on the south than on the
north side. The most heavily fertilized groves are as badly and prob-
ably more affected than those which have received less fertilization.
( This is particularly the case in connection with the application of stable
manure.) Orchards underlaid with gravel, sand or sandy loam are
more affected than those having a subsoil of fairly heavy loam containing
no sand. Orchards underlaid with plow-sole, hardpan, or extremely
heavy, poorly drained soil are likely to be affected. In orchards where
a certain area or streak of mottled leaf runs through the orchard this
corresponds to an area where the subsoil is different and usually where
it is coarser. Young buds top-worked on large trees often show mottled
leaf for several years, but gradually come out of it and attain a normal

* Circular No. 27, California Experiment Station.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1139

condition as the new tops become larger. Trees standing close to cor-
rals or manure piles where they receive a constant supply of liquid
manure are likely to be badly affected with mottled leaf.

All these observations taken together point to one conclusion ; namely,
that the most prevalent and typical form of mottled leaf is due to an
irregular supply of moisture and plant food. There should be remem-
bered in connection with the unusual prevalence of this trouble in 1910
and 1911 the following facts : The winter of 1909-10 was unusually cold,
and citrus groves suffered much more than usual from freezing. In
the winter of 1910 the rains stopped very early and the spring was a
very dry one. In the fall of 1910 the rains were late in commencing,
so that a period of nearly a year elapsed with very little rainfall. Irriga-
tion was practiced more or less thoroughly during this unusually dry
spring and fall, as well as during the summer, but all observation goes
to show that in most of the citrus groves the subsoil became much drier
than usual during that season. Orchards underlaid with either a porous
or a hard, impenetrable subsoil were most subject to this condition, as
discussed on page 1069. The result was that in irrigating only the sur-
face layers of soil were saturated, while between irrigations the soil dried
out much more than commonly. This would have the effect of giving
the tree an irregular nutrition, soil food-materials being taken up at
the time of irrigation, but being unavailable during periods of dryness.

We are led to the conclusion that this is the nature of the trouble
from the facts cited in regard to the soils upon which mottled leaf is
most prevalent, the fact that the best fertilized groves were apparently
more affected, other things being equal, and the fact that trees getting an
excess of nutriment, like those top-budded and those standing close to
manure piles, were the most affected. The fact that interior districts
suffered more than those near the coast and that trees showed more effect
on the south than on the north side indicates that where the sun was
hottest, drawing most upon the moisture, the trouble became more pro-
nounced.

We do not wish to be understood that the whole question of mottled
leaf may be settled in this manner, but simply wish to state these sug-
gestive facts. The methods by which conditions tending to produce
this condition may be improved are alluded to on page 1074.

Die-Rack.
This general term denotes cases where the branches die back from the
tips. It is not a specific disease, but as in the last two cases, indicates
that something is wrong with the tree. The trouble usually lies under-
ground, and most often denotes unfavorable soil conditions or lack of
water.

1140

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Trunk Rot (Schizophyllum commune). Figure 65.

The trunk or large limbs decay at points where they have been cut
off or injured, with the production of small, white, bracket toad-stools
upon the surface. Not parasitic on sound trees. This also affects apples,
walnuts and other trees.

Cover all large cuts or wounds thoroughly with grafting wax.

Fig. 65. — Schizophyllum trunk rot of orange.

Root Rot.
Citrus trees are affected by the " toadstool' ' or oak fungus disease
described under "Almond," whenever they happen to be planted upon
foot-hill land which has formerly grown oak trees. The trees die with
a decay of the roots and the white felty growth of the fungus is found
between the wood and bark. (See Almond.)

Twig Blight (Rclcrotinia) . See Lemon.

Wither-Tip, Anthracnose, "Tear Stain."

The wither-tip fungus described in connection with the lemon has a

somewhat similar relation to the orange. The fungus occurs abundantly

upon dead or injured twigs, leaves or trees, but is of doubtful occurrence

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1141

as a true parasite. This fungus occasionally causes a decay of the fruit
of the orange, quite different from anything seen in the lemon. The
wither-tip rot of the orange consists in a large, rather dry, brown spot,
starting sometimes on fruit while on the tree during wet weather, and
gradually spreading. These spots usually develop at places where
oranges touch each other. The same spotting and decay is quite fre-
quently found to a considerable extent in oranges held in cold storage,
particularly if the temperature is a little too low. Under such condi-
tions this fungus may develop abundantly and cause a considerable
amount of decay.

Damping Off (Rhizoctonia, Fusarium). Figure 66.

Causes the loss of great quantities of orange seedlings in the seed
bed. The plants begin to die in
spots which gradually extend,
finally involving large areas if
not checked. Two distinct forms
of the disease are recognizable,
one caused by the first named
fungus above, producing a decay
of the stem just above ground,
while the other shows itself in
dead spots on the stem at any
point.

These troubles can only be con-
trolled by strict attention to
proper methods of planting and
watering. The seed bed should
be constructed with an inch of
clean, fresh sand on top, with
heavier soil beneath. For the
inexperienced grower, particu-
larly, it is better to make fur-
rows six inches deep and about
a foot apart, planting the seed
broadcast on the ridges between.
The water may then be run in

these furrOWS and allowed tO FlG< 66.— Damping off of orange seedlings.

soak into the ground laterally, rather than being sprinkled on the
surface. Where the seed is sown broadcast all over the surface of
the bed and the water applied by sprinkling, watering should always
be done in the morning and no oftener than is absolutely neces-
sary. In many cases a good watering once a week is sufficient to keep
the soil under the sand wet enough and twice a week is almost always
sufficient until the plants get quite large. It is better to give the bed

1142

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

a good soaking at long intervals rather than to keep sprinkling on a
little water frequently. One should keep the surface as dry as possible
and after the plants get well started determine the need of water by
digging down into the soil beneath rather than wetting the bed as
soon as the surface sand gets dry.

Leaf Spot — Gum Spot. Figure G7.
Dark colored, slightly raised spots or areas* appear on the back side of

Fig. 67. — Gumming of orange leaves.

the leaf in places where it is turned up and exposed to the sun. These
spots are formed by the deposition of a gummy substance in the tissue.
The trouble appears to be in a form of gumming resulting from sunburn
on the under side of the leaf. Not serious.

Blue Mold (Penicillium italicum and P. digitatum). Figure 54.
The fruit shows a soft, moldy decay, the surface of the affected portion
being covered with a dusty mass of spores, of a blue or green color,
according as the first or second named fungus is present. The blue

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1143

fungus is somewhat more active than the green and causes occasional
infection by contact from one fruit to another.

The two fungi named above are the commonest cause of decay in citrus
fruit. Only very slightly parasitic on uninjured fruit; this decay is
practically confined, under ordinary conditions, to fruit which has been
injured in handling.

The extensive demonstrations of the United States Department of
Agriculture have established beyond question that citrus fruit will
keep indefinitely so far as blue mold decay is concerned, unless the fruit
has been bruised or injured in some manner. Such injury comes about
mainly either through cuts in the stem end made in clipping the fruit
from the tree, from rough handling during the process of hauling to
the packing house, or in grading or packing. As a result of the demon-
stration mentioned above, the whole practice of citrus fruit handling
in California has been revolutionized along the line of more careful
handling, and implements
and apparatus tending to-
ward less injury in pick-
ing and handling fruit
have been developed. Each
year 's experience goes more
and more to demonstrate
the possibilities of almost
absolute prevention of this
commonest form of decay
through careful handling.

Navel Rot — Black Rot.
(Altemaria citri) . Figure 68.

Affected oranges color
prematurely in the fall and
are affected with a dry,
black rot in the tissue below

Fig. 68. — Navel rot of orange (Altemaria citri),

the navel end. This rot is not very virulent and often remains con-
fined to one section of the orange. Occasionally in seasons of consider-
able early rain this trouble becomes quite abundant, but it is not
usually a serious matter.

Brown Rot. See Lemon.
Brown Spot. Figure 69.
A serious trouble in some localities, characterized by the development
of dark brown, sunken, dead spots of considerable size on the rind, ap-
pearing from five to ten days after the fruit is picked. Not visible on
the tree. Apparently due to climatic or other local conditions rather
than to any parasite.

1144 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

The nature of brown spot appears to be that of a premature dying of
the rind in certain spots. The fruit shows absolutely no indication of
any such trouble while it is on the tree or immediately after picking,
but after a few days have elapsed these sunken, dark colored, dead
spots begin to appear. Some years they become darker in color than
others. So far as known the trouble only affects the Washington navel
orange and is worst on the smoothest, highest quality fruit. Coarse,
rough fruit is not as likely to be affected. The trouble is usually much
more prevalent in the inland districts with hotter weather in summer,
than it is out toward the coast. The earliest picked fruit is much more
affected than that left on the trees until late in the season and, in fact,
brown spot usually disappears almost entirely after January. For this
reason the growers have a theory that the occurrence of heavy winter
rains stops this trouble. Fruit picked very early, while still green,

Fir. 69. — Brown spot of orange.

say early in October, shows the spot very decidedly, the spots remaining
green when the rest of the rind has turned to its normal yellow color.
Fruit from all sides of the tree appears to be equally affected, so far as
has been determined. Various forms of spotting may be found on navel
oranges while still on the tree, but it is certain that brown spot has no
connection with any of these, but that the true brown spots develop in
portions of the rind which are absolutely smooth and unblemished when
the fruit is picked.

It would appear that in the physiological processes which go on in the
rind during its development and ripening, some substance or principle
is present in certain areas which inhibits these normal processes. When
the orange is picked early in the season it appears that this inhibiting
substance is in an active condition and causes the area of tissue where it
is present to begin to die as soon as the fruit leaves the tree. If the
orange stays on the tree until later in the season the injurious substance

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1145

seems to disappear or be removed in some manner, leaving the rind in
a normal condition. When decolorized and treated with iodine, the rind
of oranges freshly picked in a brown spot season and locality shows the
presence of an accumulation of starch in areas here and there, corre-
sponding to about the size and distribution of the brown spots which
would have developed on the same oranges if they had been kept for a
week or two. If tested in the same way after the spots have developed,
an accumulation of starch is similarly found in the areas forming the
spots. It therefore appears that diastatic action in these areas is in-
hibited in some way.

Investigation has thus far failed to demonstrate the nature of the

Fig. 70. — Puffing of orange fruit.

initial injury, whether due to some climatic condition, lack of moisture,
or possibly an insect puncture. It is certainly not due to frost or cold
weather. The fruit from certain groves seems to show the trouble more
than that from others, and it is possible that the same is true of individ-
ual trees, but this has not yet been determined.

See Bulletin 203, page 47, California Experiment Station.

Splitting.
The fruit cracks and splits on the tree before maturity. Varies from
year to year in abundance. Apparently caused by climatic or seasonal
conditions causing irregularity in the growth of the fruit.

1146 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Puffing. Figure 70.

Characterized by a condition of the rind indicated by the above name.
The surface of the fruit becomes rough and uneven, due to a spongy
condition of the rind. The whole orange becomes soft and structureless
with an unnatural sweetness.

This trouble varies with the season and appears to be connected with

soil moisture conditions.

Stain.

A discolored, darkened condition of the rind developing after the

fruit has been picked. Occurrence apparently confined to fruit which

has been subjected to low temperatures, either in transit or cold storage.

Shoulder Spot — Stem End Spot. Figure 71.
A dry, brown, dead spot or area develops upon the orange about the
stem end or at one side of the latter on the "shoulder'' of the fruit.
These spots are primarily dry and not of the nature of decay, but they
often become infected with blue mold or other fungi. Often, too, they
are covered with a growth of a Cladosporium fungus, which forms an
almost black mold upon the surface. These spots may also become in-
fected with the wither-tip fungus. This form of spot or deterioration
at the stem end of the orange occurs only in old fruit, most commonly in
the last Washington Navels of the season. It is especially abundant in
seasons following years of exceptional drouth, particularly when the
fall rains are very late in commencing. The normal deterioration of the
orange when its physiological life is ended begins at the stem end and
the present trouble appears to be simply a somewhat premature death
of the tissue, owing to the age and weakness of the fruit. This is made
more pronounced, as has just been suggested, by a long, dry season
during the preceding fall which weakens the tree and thus reduces the
vitality and length of life of the fruit.

Miscellaneous Spots and Blemishes.
Oranges and other citrus fruits are subject to a variety of surface
spots and blemishes. In a paper prepared by Dr. J. Eliot Coit of
this Department, published in the California Cultivator of March 16,
1911, about fifty different forms of such blemishes are classified and
described. These are classified as being caused by insects, fungi, me-
chanical injuries and physiological troubles. Those which we have
described above are by far of the most importance, although occasionally
in certain seasons some other form of spotting, blemish or injury
occurs which attracts considerable attention for a temporary period.
Frequently in such cases certain mold fungi develop upon the surface
of the areas affected and are sometimes taken for the cause of the trouble.
This is particularly the case with a species of Cladosporium which pro-

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1147

Fig. 71. — Shoulder spot of orange.

1148

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

duces a dark brown mold on the surface of the spots. This fungus, how-
ever, has nothing to do with originating any form of spot upon citrus
fruit.

Palm (Phoenix canariensis, dactylifera, etc.).
Leaf Spot (Graphiola phoenicis). Figure 72.

Injures the lower leaves of the date palms with the production of
minute black protuberances of the fungus, mostly on the lower side of
the leaves.

Remove all affected leaves, and if this fails to control the trouble the

Fig. 72. — Palm leaf spot (Graphiola phoenicis).

Fig. 73. — Palm leaf spot (Sphaerodothis
neowashingtoniae) .

trees may be sprayed with the ammoniacal copper carbonate. Bordeaux
mixture is effective, but disfigures the tree.

Palm (Washingtonia) .
Leaf Spot (Sphaerodithis neowashingtoniae) . Figure 73.

The leaves become covered with small, elongated, black, slightly ele-
vated spots of the fungus growth, and die.'
Affected leaves should be removed.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1149

PEA.
Mildew (Erysiplie polygoni).
Covers the plants and pods with a white mildew. Most prevalent in
wet weather and is usually only serious on the winter crop.

Dust the vines with dry sulphur at the first appearance of the trouble.
In cloudy weather spraying with Bordeaux mixture is most effective.

Blight (Ascochyta pisi).
Produces black spots on the leaves and pods and seriously injures the
vine. Most troublesome in wet weather.

i 0 _, 1

Fig. 74. — Curl leaf of peach (Exoascus defor-
mans).

Spray with Bordeaux mixture if the trouble is serious
enough to make it profitable.

PEACH.

Leaf Curl {Exoascus deformans) . Figure 74.

Many of the leaves are curled and deformed in a char-
acteristic manner as they develop in the spring. These
afterward wither and fall, together with much of the
fruit. A new crop of leaves then develops in a normal
manner.

Spray with Bordeaux mixture or lime-sulphur just fig. 75. Peach

before the buds open in spring. blight (Coryneum

r xr a beyennkii).

Blight (Coryneum oeyerinkii). Figure 75.
Dead spots appear on the young shoots during the winter, particularly
at the buds. The buds are killed, together with much of the young
8— Bul. 218

1150

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

growth or fruiting wood. During the spring rains a jelly-like gum
exudes in large quantities from these dead spots.

Spray with Bordeaux mixture during November and again with the
same material or lime-sulphur just before the buds open. A combined
spraying may be made for blight, curl leaf and peach worm by using
Bordeaux in the fall and lime-sulphur in the spring.

See Bulletin 191, California Experiment Station.

Mildew (Podosphaera oxyacanthce) .

A white powdery mildew appearing on the leaves during the summer.

Not serious.

Die-Back. See Almond.

Fig. 76. — Little peach.

Little Peach. Figure 76.
Some or all of the peaches remain small and undeveloped, while the
normal fruit is reaching full size.

This is not the dreaded little peach disease of eastern states, but
appears to be the effect of imperfect pollination. Its occurrence has
been found to follow seasons of much rainfall during the blossoming
period. Not serious. In some cases Fruit Drop occurs from the same
cause. See Almond.

Brown Rot. See Apricot.

Cbown Gall, Root Rot, Sour Sap, Rust. See Almond.

Gummosis. See Cherry.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1151

Split Pit.
The pit cracks and splits into many small fragments while the fruit
is still on the tree. Cause not known, but apparently climatic. Possibly
due to frost injury in spring.

Fruit Gumming.
Masses of gum appear on the surface of the fruit, which may be traced
through the flesh to their origin in the pit. Apparently somewhat con-
nected with the last trouble.

Little Leaf — California Yellows. Figure 77.

Characterized by the development of spindling, yellow, sickly looking
shoots on the new growth, with small, narrow, yellow leaves. The leaves
along the shoots drop off during the summer, leaving tufts at the ends.
Fruit fails to develop, shrivels and drops. Worst on trees from three to
seven years old.

This trouble also attacks other stone fruits, walnuts, pecans and other
trees. Always worst on lighter, drier soils, this feature showing itself
by the more pronounced occurrence of the disease on trees standing in
sandy streaks or slight elevations in the orchard.

This trouble has no relation to the true Eastern peach yellows, but is
decidedly climatic and seasonal in its appearance. Occurs mostly follow-
ing unusually dry seasons, on trees standing in light soil or one under-
laid with a coarse, sandy subsoil. Trees on a fairly heavy subsoil, or
those which have received abundant irrigation throughout the preced-
ing season are decidedly free from the trouble even in the worst affected
localities. Appears similar in nature to " mottled leaf" of the orange,
and, in fact, orange trees growing near peaches affected by ' ' little leaf '
show a typical "mottled leaf" condition. Many other kinds of trees are
also more or less affected.

The typical peach disease has been seen only in the San Joaquin
Valley, in the most sandy regions.

In most cases, regular irrigation during the summer shows a marked
effect in controlling this trouble. Such irrigation should be given partic-
ularly in the latter part of the season, after the crop is off, especially
when the rains are late in commencing.

Climatic Effect.
The trees fail to leaf out properly in the spring and seem to become
confused, so to speak, as to the season. Later in the summer the trees
may bloom and leaves begin to appear, but the tops usually die back
nearly to the forks of the tree and sometimes the trees die entirely. If
not too badly affected, the tree sends out new sucker growth from the
trunk and base of the main limbs. Plums, apricots, apples and other
trees are sometimes affected.

1152

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

This trouble is one which occurs mostly in the southern part of the
state as a result of unseasonable climatic conditions. It is usually most
pronounced in seasons when a period of warm, stimulating rains in the
winter is followed by a long, cold spring. Similar results are also pro-

Fig. 77. — Little leaf of peach.

duced by an abnormal, dry fall, throwing the trees into a dormant con-
dition, followed by warm, spring-like weather accompanying the winter
rains. These combinations and various others often have unfavorable
effects upon trees which are accustomed to a definite resting period dur-
ing the winter. Many peculiar diseases of deciduous fruits described

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1153

in this bulletin under various names, such as "die-back," "yellows/
etc., are no doubt contributed to by such disturbances in the normal
period of dormancy. Every few years there is usually a season, espe-
cially in the southern part of the State, when deciduous trees are badly
affected in such ways as these.

Following such an attack, trees should be pruned back to healthy,
vigorous wood, when they will usually form a new top and come back
into good condition again. With peaches it is noticeable that varieties
of the saucer or Peen To type are not affected in this manner, as are
the Persian varieties.

PEAR.
Scab (Venturia pirina). Figure 78.

Similar to apple scab, which see. Develops as a dark brown fungus
in spots on the young pear or even in the blossoms. Also on the under

Fig. 78. — Pear scab (Venturia pirina).

side of the leaves. Much worse in sections with abundant moisture in
spring. Often causes much of the fruit to fall at the very first of its
development, while the affected pears which remain on the tree are
scabby and much deformed.

1154

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Spray with Bordeaux mixture. See Apple Scab. Combined spraying
may be done for scab and codling worm.

See Bulletin 163, California Experiment Station.

Blight (Bacillus amylovorus). Figure 79.
The leaves, blossoms and young fruit wither and turn black on the
affected portions but do not fall, remaining tightly attached to the
twigs during the winter after the green leaves have fallen. Caused by
a bacterial organism which produces its infection largely through the
blossoms, being carried by insects from tree to tree. The infection pro-
ceeds downwards through the inner bark of the twigs and branches and
when working vigorously the blight kills the twigs or whole branches

very rapidly. The dis-
ease often runs down into
the large limbs, where it
remains alive over winter,
producing the so-called
' ' hold-over ' ' blight, which
is a source of infection
during the following sea-
son.

The blighted twigs,
branches or trunks show
a red, sappy, juicy condi-
tion of the inner bark
when infected with the
true pear blight organism.
If the disease is fresh and
active the bark when cut
into is very juicy, exuding
the slightly sticky sap
quite freely and showing
the characteristic bright
red color in the inner
bark. This symptom is of
importance in distinguishing true blight from such troubles as sour sap,
crater blight and black leaf.

In the smaller twigs and branches the organism dries out and becomes
entirely dead. Infection also takes place through the agency of biting
insects in the young shoots and suckers. Through this means the dis-
ease frequently gets into the trunk of the tree and also down into the
roots. Here it spreads and causes the death of the tree by slow de-
grees, due to the destruction of the inner bark of the trunk or main
roots. In such cases the leaves of affected trees take on a peculiar

Fig. 79. — Pear blight (Bacillus amylovorus)

Bulletin 218] CALIFORNIA PLANT DISEASES. 1155

bronzy reddish coloration in the fall, which is quite characteristic to
the experienced eye.

From the "hold-over" blight in the trunks and large limbs an in-
fectious sap exudes when growth starts in the spring, which sap con-
tains myriads of the blight organism. This sap is attractive to insects,
which, in feeding upon it, get the blight bacteria upon their bodies and
mouth parts; and transfer them to the blossoms or green shoots of other
trees, thus spreading the infection.

Cut out and destroy all diseased parts, taking care particularly in
the summer time to cut far below any visible sign of the disease, even
at the sacrifice of considerable fruit. The pruning instruments should
be kept constantly disinfected, using a solution of corrosive sublimate
(bichloride of mercury) 1-1000.

Trees badly affected in the trunk or roots should be taken out and
destroyed, unless it is possible to cut out all the affected tissue of the
inner bark, which can be identified by its reddish color. In some cases
the affected tissue can thus be removed, cutting back to sound bark and
wood on all sides, and the tree saved. In doing this work the tools
should be thoroughly disinfected, and the wounds saturated with the
disinfectant and afterwards painted over with white lead paint.

See Bulletin 184, page 221, and Bulletin 203, page 18, California

Experiment Station.

Black Leaf.

In this disease one side or one limb of the pear tree dies and the
leaves turn black and hang on for some time. The effect is quite similar
in a general way to that of pear blight, but there is no sign of the
presence of the pear-blight-causing organism as indicated by the red,
juicy inner bark of limbs and twigs affected with the real blight. Some-
times there is connected with black leaf a dying of the bark extending
in a narrow strip of uniform width down the trunk to the ground. All
phases of this disease are distinguished from the true blight by the
fact mentioned that there is not present the red, juicy condition of the
inner bark, but the bark simply dies down and becomes very hard and
dry from the first. This trouble also often occurs in orchards where
the blight is not present and does not show the characteristic spreading
of blight from tree to tree through the blossoms or by infection of
young shoots and suckers.

The disease appears to be more of the nature of sour sap, connected
most commonly with an excessive amount of moisture in the ground
during the winter and spring. Where individual limbs are affected or
narrow strips of bark on the side of the trunk, it appears that certain
roots have been badly injured and that the portions affected above
ground correspond with such roots.

1156 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Crater Blight.
This term is a rather common one among pear growers, but is not
applied to any very definite form of disease. It is supposed to signify
a dying of certain spots or patches of bark situated on the limbs or
trunk. In these patches the bark becomes rough on the outside and dark
colored beneath the surface. Some injury of this sort appears to be
connected with the disease described above, the bark dying in certain
spots rather than in a strip up and down the whole length of the branch
or trunk. True pear blight may also cause a similar effect by running in
from a small shoot or fruit spur, but many cases of both black leaf and
crater blight occur without the presence of the pear blight organism.
Frequently, what is called crater blight is renlij nothing more than the
normal roughening of the bark of the pear tree as it grows older. In
this tree the bark begins to crack and roughen in patches on the trunk
and main limbs, and its normal condition has sometimes the appearance
of the outbreak of some disease.

Cukly Bark.
This is somewhat similar to the above, the bark cracking in concentric
rings in spots upon the surface of the main limbs. It is not of any seri-
ous consequence.

Fruit Drop.

The young fruit drops from the tree while still very small and im-
mature. Due to imperfect pollination. Ordinarily, results simply in
a desirable thinning of the fruit, but sometimes a large part of the
crop drops from this cause. May also be produced by frost affecting the
fruit soon after setting. Such fruit may remain on the tree and con-
tinue to grow for some time after the frost occurs before falling.

Ringed Fruit.
Some years many pears are found at maturity with a scabby ring or
belt of considerable width extending around the fruit. The pears are
constricted in this portion, owing to interference with the growth. It
is evident that this effect comes about through some injury to the pear
when it is quite young. This is a frost effect, and pears in a very small,
young condition may be seen with similar rings about them in a season
when much damage has been caused by late frost.

PECAN.

Rosette or Frizzies.

While not an important crop in California, there is considerable inter-
est at present in pecan planting, and it is desirable to call attention to
this disease.

Shoots develop of a spindling, yellow, frizzly appearance, continually

Bulletin 218] CALIFORNIA PLANT DISEASES. 1157

dying back and shooting out anew from axillary buds. The trouble
is very similar, if not identical, with that affecting the walnut and also
seems to be related to what we have described as the California peach
yellows. It is probably the same as the pecan rosette, which occurs in
the southeastern states.

PLUM.

Die-Back, Crown Gall, Sour Sap, Rust. See Almond.

Brown Rot. See Apricot

POMELO. See Orange.

POTATO.

Scab (Oospora scabies). Figure 80.
The growth of this fungus on the surface of the potato produces a
rough, scabby condition greatly injuring its appearance and selling

Fig. 80. — Potato scab (Oospora scabies).

value. Possibly this or a similar condition is also caused by other

agencies than the fungus above named.

Use clean seed, treating before planting or cutting by soaking one and

one half hours in a solution of one pint of formalin to thirty gallons of

water. If the soil is badly infested, do not use it for potatoes for several

years.

Early Blight (Alternaria solani).

Produces dead spots on leaves. Not serious in this State.
Late Blight (Phytophthora infestans) .

Causes death of the leaves and decay of the tubers. This fungus de-
velops only when considerable moisture is present in the air, and its
attacks on potatoes in California are therefore confined to those grown
in the winter season or in very foggy localities near the coast. Under

1158 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

either of these conditions the disease may develop very disastrously and
suddenly, killing down and blackening the potato tops, as though they
were struck by frost.

Spray with Bordeaux mixture immediately after rains or during
foggy weather, if treatment seems necessary.

Dry Rot (Fusarium oxijsporum) .

This fungus causes a decay of the stems and main roots, resulting in
a gradual wilting and dying of the plants. Affected potatoes show a
dark ring just inside the surface and from this the fungus may spread
all through the tuber, producing a dry rot. Potatoes in storage some-
times develop this quite extensively. The parasite is thus carried in
the seed and can be controlled only by planting potatoes which are
free from this fungus.

Use seed known to be from a crop not affected by this trouble and
do not plant potatoes in badly infested soil.

Brown Streak.
The tubers show a brown ring or streaks in the flesh just beneath the
surface, and sometimes throughout. This is sometimes confused with
the disease preceding, but there appears to be a distinct trouble of this
sort in which no fungus can be found. Occurs particularly in foothill
and mountain districts. Apparently clean seed from outside districts
develops the trouble in the first crop in affected regions.

Black Leg (Bacterial).

The disease appears when the plants are quite young and small. The
affected plants are of a pale color, with the leaflets rolled inward and
the shoots unnaturally straight. The stem is conspicuously blackened
below ground, or in some cases somewhat above ground, especially in
moist weather. The seed tuber decays prematurely.

This trouble, which appears to be due to a definite bacillus, has oc-
cured quite extensively in southern California.

Do not plant seed potatoes from affected fields. Soak the seed in for-
malin solution as for scab. Avoid planting in affected soil.

Little Potato.

Clusters of abnormally small tubers develop near the surface of the
ground or even upon the stems above ground.

Apparently due to root or stem diseases which cause decay of the
parts below ground. May be caused mainly by Rhizoctonia, which soil
fungus is very common in California. In the latter case numerous
small, black sclerotia, the resting stage of the fungus, are commonly to
be found clinging to the surface of healthy potatoes of normal size, with
apparently no ill effect. Figure 81.

Use same treatment as for scab.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1159

Fig. 81. — Rhisoctonia on potato.

1160 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

General Directions for Potato Planting.

Use seed from a field unaffected by disease of any sort and plant only
potatoes which are free from decay and any internal discoloration.

Avoid planting on land where potatoes were affected the previous year
with any disease of the parts below ground.

Before cutting the seed potatoes soak them for one and one half hours
in a solution of one pint of formalin to thirty gallons of water.

PRUNE. See Plum.
Shrivels.
The fruit becomes discolored on one side, shrivels and dries before
maturity, remaining small and worthless.

Prunes are grown in California very largely without irrigation, and
this trouble is undoubtedly due to a lack of water. It occurs particularly
in dry seasons when the winter rains cease very early. Under such
conditions the water supply fails early in the season and the fruit has
not sufficient moisture for its full development. The foliage also suffers
from the same cause, many of the leaves fall, red spider becomes prev-
alent, hastening the fall of the leaves and further weakening the tree,
and the fruit is exposed to sunburn, which hastens its premature
maturity.

PUMPKIN.
Mildew (Erysiphe cichoracearam) .

This white powdery mildew often covers the leaves of pumpkin vines.
Not serious.

Wilt (Bacillus tracheiphilus) .

The vines wilt and die from no apparent cause. A decay develops
in the stem which appears to be caused by a bacterial organism. So far
as investigated, this does not seem to agree entirely with the charac-
teristics of the disease caused by the organism named above, which
occurs in other parts of the country.

QUINCE.
Blight (Bacillus amylovorus) . See Pear. Not serious.

Little Leaf. See Peach. Figure 82.
Black Knot.

Large black knots or swellings develop abundantly on the trunk and
branches. This condition is so common and characteristic on the quince
in California that it has come to be regarded as a normal one. It is a
fact that there appears to be no particularly bad effect from such knots,
as the trees continue to live and bear fruit in an apparently healthy con-
dition. Whether or not these swellings are due to the specific organism
of root knot (Bacterium tumefaciens) has never been determined.

IIUU.ETIN218]

CALIFORNIA PLANT DISEASES.

1161

Fig. 82. — Little leaf of quince.

1162

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

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Bulletin 218] CALIFORNIA PLANT DISEASES. 1163

ROSE.
Mildew (Sphaerotheca pannosa and S. humuli). Figures 83, 84 and 85.

Roses in California are commonly affected with two different powdery
mildews quite different in appearance from one another. The first
named is seen most characteristically on the hybrid roses and is partic-
ularly severe on the Crimson Rambler. It forms a thick, dense, felty
white growth upon the green shoots, buds, and young leaves more than
on the surface of the older leaves. This does not affect the tea roses.
The latter are particularly susceptible, however, to the second fungus
named, which produces a more delicate fungus growth upon the leaves
and blossoms rather than the stems, giving them a crinkled appearance.

The most effective treatment for these and the following rose troubles
consists in spraying the bushes occasionally with a solution of sulphide
of potash (liver of sulphur), one ounce to three gallons of water. Spray
the under side of the leaves as well as the top and make up the solution
fresh each time the spraying is done. If the bushes are also affected
with plant lice an addition of tobacco extract or cheap soap may be made
to the spray. In bad cases of mildew further relief may be obtained by
dusting the bushes thoroughly with flowers of sulphur while they are
still wet with the spray.

Different varieties vary greatly in susceptibility, and the ordinary
grower will find the most satisfaction by discarding the most susceptible
kinds and growing others which are less liable to disease.

Rust (Phragmidium subcorticium) . Figure 86.

Affects the hybrid roses, causing the leaves to turn yellow and fall,
with black or bright orange pustules of rust spores on the under side.

See Mildew.

Black Spot (Actinonema roscc).

Produces purplish or discolored areas of considerable size on the sur-
face of the leaves, causing them to drop.

See Mildew.

Cane Blight. Figure 87.

Affected wood turns a dark purplish or black color, with a sharply
defined line between the sound and diseased bark.

This trouble is common in California and due to a fungus which is
apparently undescribed in plant disease literature. It infects stubs left
in pruning and often develops down into the main branches, seriously
injuring the bushes.

May be largely avoided by proper pruning.

1164 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Fig. 85. — Rose mildew (Sijhaerothcca humuli) .

Bulletin 21S]

CALIFORNIA PLANT DISEASES.

1165

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1166

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

SORGHUM.

Smut (Sphacelotheca sorghi and S. reiliana).

This crop is affected by two different smut fungi in California, the
former developing a black, dusty mass of spores in place of the seeds
of the grain, while the latter breaks out in swellings on the plant itself,
containing the black, smutty spore masses like corn smut.

Use seed from fields free of smut.

STRAWBERRY.
Leaf Spot (Sphaerella fragarice). Figure 88.
This fungus produces on the leaves numerous small dead spots with
dark purple margins.

Fig. 88. — Leaf spot of strawberry (Sphaerella fragariae).

In badly affected fields mow the leaves closely and burn them.
Spray with Bordeaux mixture if the trouble is serious enough to war-
rant this.

Mildew {Sphaerotheca castagnei).

A white surface mildew. Not serious.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1167

SQUASH. See Pumpkin.

SWEET POTATO.
Stem Rot — Wilt (Fusarium).
The plants gradually die and wither away in the field, the stem and
roots being affected by this dry rot fungus.

Use seed from an uninfested locality and plant on fresh land as far
as possible.

Gather and burn all affected vines.

Black Rot (Ceratocystis fimbriata).

Characterized by black, dry, scabby
patches developing on the potatoes while
they are in the ground.

Do not use seed from infested fields or
plant again on the same ground.

Soft Rot (Rhizopus nigricans). Figure 89.

A soft decay of the potatoes in storage,
caused by a black mold which appears on
the surface.

Handle the potatoes carefully while
green and let them cure or dry thoroughly
before storing. Pack in dry sand for long
keeping.

SYCAMORE.

Blight (Gloeosporium nervisequum) .

The young growth is killed back as
though by frost. This fungus affects syca-
more trees quite universally just after they
leaf out in the spring.

No practical means of control, except by
spraying specimen or particularly choice
trees with Bordeaux mixture just before
they leaf out.

Fig. 89. — Sweet potato rot
{Rhizopus nigricans).

Mildew (Microsphaera sp.).
A powdery mildew has been found in nurseries on the Sycamore.

TOMATO.
Damping Off (Rhizoctonia, Fusarium. Sclerotinia, Botrytis). Figure 90.

Young plants in the seed bed decay at the surface of the ground and
die away in large numbers. Much worse in damp, cloudy weather and
sometimes difficult to control under such conditions. Caused by various
fungi. The trouble is checked by bright sunlight and dry weather.

Make the seed bed soil as sandy as possible.

1168

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Avoid excessive watering when the weather is favorable to this
trouble; water only in the morning and on sunny days so far as pos-
sible. Give the plants plenty of ventilation and fresh air.

Summer Blight (Fusarium).
Occasional plants here and there in the field gradually turn yellow,

sicken and die, after reaching consider-
able size. A dry rot is found in the stem
and roots, caused by a fungus. This
fungus does not infest the soil in the
field and the disease may be abundant
one year and totally absent the next
year in the same field. Affected plants
sometimes do not show the fungus until
in the last stages, and there is some
doubt as to the identity or cause of this
trouble. Plants may become infested in
the seed bed under conditions favorable
to damping off. It is possible that two
different diseases are confused in this
trouble.

Keep the seedlings as free from damp-
ing off as possible and use only the best
plants for planting in the field. Select
seed from healthy plants.

See Bulletin 175, California Experi-
ment Station.

Winter Blight {Phytophthora infestans).
Figures 91 and 92.

The leaves and stems are suddenly
blackened and killed and the fruit spots
and decays. The whole effect is quite
similar to that of frost. Caused by the
potato blight fungus. Never occurs dur-
ing the summer, but occasionally comes
on to a disastrous extent on the winter
shipping crop following early fall rains, or in early spring plants.
Spray with Bordeaux mixture immediately following rain.
See Bulletin 175, California Experiment Station.

Blossom End Rot. Figure 93.

The end of the tomato becomes discolored and affected with a dry

rot which spreads to a greater or less extent. Tomatoes of all sizes are

affected, particularly those which are half grown. No definite cause has

been found for this trouble, which varies in abundance from year to

Fig.

90. — Damping off of tomato
seedlings.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1169

Fig. 91. — Winter blight of tomato fruit (Phytophthora infestans),

1170

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

year. Apparently worse on dry ground where the vines do not receive
regular irrigation.

Fig. 92. — Winter blight of tomato leaf (Phytophthora infestans) ,

Fig. 93. — Blossom end rot of tomato.
Stem Rot (Sclerotinia libertiana).

A dry rot of the stem and wilting of the vine. Found only in green-
houses. Not serious.

Bulletin 21S]

CALIFORNIA PLANT DISEASES.

1171

Leaf Spot (Scptoria lycopersici) .
Small dead spots appear on the leaves. Not common or serious.
Found mostly in seed beds.

Root Knot (Nematode).
Galls or swellings appear all over the roots and the plants sicken and
die. Infection takes place in the seed bed. Carefully discard affected
plants in field planting and change the soil in infested beds.

TURNIP. See Cabbage.

Fig. 94. — Leaf spot of vetch (Colletotrichum sp.).

VETCH.

Leaf Spot. Figure 94.
Small black spots appear on the leaves and the whole plant is more or
less killed. Does some damage on vetch planted for a cover crop ;
usually associated with the cottony mold fungus, Sclerotinia. Caused
by a fungus, probably a species of Collet otrichum.

1172

UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

WALNUT.

Bacteriosis (Pscudomonas juglandis). Figures 95, 96 and 97.

Blight.
Causes a black spotting on the surface of the young nuts, many of
which drop prematurely. Affected nuts which reach full size have the
contents blackened and spoiled. The shoots are also affected with the
production of black, canker-like areas, most of which heal out as the
wood hardens, leaving wounds and cankers of considerable size. Many
of the small fruit spurs and twigs are entirely killed, but the disease

Fig. 95. — Walnut blight on nuts (Pseudomonas juglandis) .

does not kill large limbs or whole trees. The leaves are also affected in
black spots.

The disease varies in abundance from year to year, being most preva-
lent in seasons with much fog and moisture late in the spring.

No practical remedy has been found for this disease, but the problem
has been largely solved by the development of immune varieties. Such
trees are now available to a limited extent and must soon supplant the
present plantings of seedlings or susceptible kinds.

Some control may possibly be obtained by spraying with Bordeaux
mixture or sulphur sprays just before the buds open. The expense of
spraying walnut trees thoroughly is so great, and so much time is re-
quired to thoroughly cover trees of this size, that we have no faith in a
satisfactory solution of the walnut blight problem along this line.

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1173

On old groves liberal fertilization with nitrogenous fertilizers, to-
gether with the use of green manure crops, will go far towards making
up for the losses caused by the disease.

Most walnut groves would be benefited by more irrigation than they

Fig. 96. — Lesions on blighted walnut twigs (Pseudomonas juglandis) .

receive at present, particularly during the winter and in the fall after
the crop is harvested.

See Bulletin 203, page 24, California Experiment Station.

Trunk Rot {Schizophyllum commune). Figure Go.
The trunk or main branches rot, with a production of small, white
bracket toadstools on the surface of the affected wood. This fungus
does not affect sound trunks, but follows deep wounds, bruises, heavy
cutting, sunburn or other injuries. The wood of the English walnut
is particularly susceptible to this form of decay.

1174

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Fig. 97. — Blighted walnut twigs (Pseudomonas juglandis) .

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1175

All severe cuts or wounds should be carefully covered with grafting
wax to allow healing over without decay. In top-grafting walnut trees
this should be given special attention or serious decay may follow.

Sun Burn. Figure 98.
Serious damage is sometimes caused from this source, both on the
fruit and the tree. In the latter case the trunk is usually affected, dead
areas developing in the bark on the sunny side. This originates mostly
in winter when the nights are cold and the days bright and sunny. Not
usually serious on thrifty trees growing in good soil. Black walnut

Fig. 98. — Walnuts affected by sun burn.

trunks with rough bark are not affected by sun burn, so that trees
grafted high on such trunks are immune.

On the fruit the sun sometimes has a disastrous effect, causing a
blackening and burning of the husk on one side during extremely hot
weather in summer. The meat is also blackened, and the husk sticks
to the shell so that separation is difficult and a black spot is left. Thrifty
trees are less affected, particularly when supplied with an abundance
of moisture at the root. Individual trees or varieties vary in suscepti-
bility to this trouble, and this quality should be considered in planting
in localities where trouble from sunburn is likely to occur.

Perforation. Figure 99.
The shell fails to develop properly, being only partially formed, with
numerous openings and thin places. This appears to be simply a lack
of development due to climatic conditions and occurs in seasons with a
dry spring and a dry, hot summer. Seems worse on trees attacked by
aphis.

1176

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

Erinose.

Blister-like swellings appear on the leaves, sometimes becoming very
abundant. This trouble is caused by an insect, so minute that it is not
visible to the eye.

Not serious or requiring treatment.

Fig. 99. — Walnut perforation.

Die-Back. Figure 100.

The limbs die back from the ends, sometimes for only a short dis-
tance and sometimes down to the main forks of the tree. All the limbs
or only a part of them may be affected. Two general types of die-back
may be distinguished, one on the old trees, particularly "hard shells,"
which die back slowly all over the top, and another in young trees from
two to ten years old, which die back suddenly during a single winter in
part or all of the limbs, or sometimes the whole tree dies back clear to
the ground.

The former type of die-back affecting old trees occurs mostly on light
soils where the trees are getting old and the roots find insufficient moist-

BULLETIN 21 S |

CALIFORNIA PLANT DISEASES.

1177

ure. Such dying back is also hastened by lack of cultivation, irrigation
and plant food, which lack becomes more pronounced as the trees grow
older and the tops and roots more crowded. The only remedy for this
trouble is to thin out the trees where they are too closely planted and
give the soil better care. Most of these old hard shell orchards, even at
best, have now become so unprofitable and undesirable as to make it
seem better for the owners to cut down the trees and use the land for
some other purpose.

The second form of die-back mentioned, that occurring in young trees
which have formerly been thrifty, killing them down to the forks or
even to the ground, is a very serious matter at present in some districts.
The trouble shows usually to a
greater extent in a certain por-
tion of the orchard or in certain
orchards worse than in others
near by. It developed more ex-
tensively in the spring of 1911
than ever before, when a great
many trees which had seemed
healthy and vigorous the pre-
vious fall were found to be al-
most entirely dead in the spring.
Affected trees failed to leaf out
at the proper time and more or
less of the top proved to be either
entirely dead or developed very
slowly later in the season. Such
trees often threw out new growth
or suckers toward the base,
which made a very vigorous
growth, while the tops were dead
or very slow in coming out. The
leaves which finally developed
from the affected limbs had a yellow, sickly appearance.

This trouble is more or less the same as that described under wralnut
'Yellows," and evidently has been caused by the abnormally dry sea-
son of 1910. The disease is practically the same in its nature as that
described as the "Little Leaf" of the peach and shows similar relations.
Trees standing over coarse, dry subsoil or those which had for any rea-
son become drier than usual during the fall of 1910 showed the trouble
the worst. Young trees under ten years of age showed the trouble
worse than older ones. It is a common practice in some of the worst
affected districts to grow alfalfa between the walnut rows and in groves
or portions of groves which for this reason became drier than the aver-

Fig/100. — Die-back of walnut.

1178 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

age late in 1910 the trouble has been worse. Even in some fairly heavy
soils the packing of the surface on account of several years' irrigation
and handling of alfalfa prevented the moisture reaching the subsoil and
thus the same effect was produced. Frost was also responsible to a
greater or less extent for the dying back of trees in dry ground.

Trees affected in this way should be pruned back to good live wood,
if not too far gone, and it is to be expected that a new top will soon be
produced. By proper attention to irrigation late in the season, espe-
cially in dry years, it is not to be expected that the trouble will occur
again save in soils most unsuitable for walnuts on account of coarse
subsoil near the surface. We may say here that in choosing crops for
interplanting walnuts, it is not desirable to let the ground remain in
alfalfa too long unless an abundant water supply is available, and one
can be sure by actual examination that the soil is sufficiently moist at
all times, both for the alfalfa and for the trees. In any event, it is
ordinarily best to leave a cultivated strip at least eight feet wide on
each side of the tree row, and as the trees grow older it is better to plow
out the alfalfa and grow some annual crop which will receive regular
cultivation, as well as irrigation.

Yellows.
Spindling, yellow shoots develop which usually die back from the
tip. All degrees of the trouble may occur from slightly unnatural
yellowing and slenderness of the normal shoots to the production of
masses of small, yellow shoots, with continual dying back. This affects
the English walnut, and is even more pronounced on the Northern
California black walnut in certain seasons and places. It has been
abundant even on black walnut trees of large size in some parts of
northern California during the last two or three years, and very preva-
lent in nursery trees of the northern California species grown in the
southern part of the State. At the same time and in the same nurseries
seedlings of the southern California black walnut have never shown the
slightest indication of this trouble. This disease appears to be the
same which affects the peach (which see), and also to some extent the
pecan, apple, and many other trees. It is probably due to a climatic or
soil condition rather than to any parasite. Conditions which result in
sour sap and similar troubles in the stone fruits seem to be related to
this disease, and it is very likely due to a disturbance of the dormant or
resting condition through which these trees normally pass during the
winter. Also seems to be connected with lack of rain or irrigation late

in the season.

Crown Gall — Black Knot. Figure 101.

Walnut trees are affected in some instances with large knots or
cankers on the trunk just below ground or a slight distance above

Bulletin 218]

CALIFORNIA PLANT DISEASES.

1179

ground. This trouble is not a common one, but seems to occur in some
districts more than others. Whether such knots are due to the real
crown gall organism (Bacterium tumefaciens) has never been de-
termined, but their appearance leads one to suspect that they originate
from infection of scars or wounds on the trunk by this parasite. Known
only upon the English walnut.

As soon as the trouble appears cut out the diseased tissue, disinfect
with strong bluestone solution and paint over the wound.

Fig. 101. — Black knot on walnut trunk (Bacillus tumefaciens) .

Crop Failure.
It is a very noticeable fact in connection with the California walnut
industry that the total product of the groves of the State is not mate-
rially increasing, although the acreage has multiplied many times during
recent years. This is due to a very general condition of poor produc-
tion in the large walnut-growing sections of the southern portion of the
State. The older groves, although by no means at an age when they
should be deteriorating, show very little tendency to increase their
yield, and in many cases are gradually going back. The quality and
size of the nuts, as well as the quantity, is also a source of complaint.
Many of the nuts which mature are empty or poorly filled with shriveled,
light weight meat, giving the nut when cracked an unattractive appear-
ance.

1180 UNIVERSITY OF CALIFORNIA — EXPERIMENT STATION.

Trouble of this nature is quite commonly attributed to walnut blight,
with which disease, however, it has nothing to do. There is probably
no one cause or reason for this condition. It is due, generally speaking,
to a loss of vitality in the trees, brought about mostly by unavoidable
mistakes made in planting when the industry was new and experience
in walnut growing very limited. In the first place, all the older groves
were planted with the trees too close together. At the common distance
of forty feet the branches begin to touch before the trees are ten years
old, and by the time they reach full bearing age, the ground is com-
pletely shaded and the tops of the trees form a solid mass throughout.
This condition is extremely unfavorable to walnut production, and as
the groves grow older is the cause of more and more lessening of the
crop.

Another factor in walnut deterioration has been the common idea
that these trees require very little cultivation, irrigation, or fertilization
and the very irregular attention which they have received in this respect.
It is true that many walnut trees exist which receive no cultivation
whatever and produce very good crops. Such trees, however, usualty
stand out by themselves with full exposure on all sides, and moreover,
while the ground about them is not cultivated, it is at least subject to
uniform conditions. The walnut tree seems to particularly resent rad-
ical changes in soil treatment. It may do well with no cultivation and
will do better, other things being equal, with good cultivation, but it
is decidedly injured by irregular treatment in this respect.

Another feature of the situation is the fact that all our older groves
are seedling trees, growing thus on their own roots. The English wal-
nut root of the type most commonly grown in southern California is
thrifty and vigorous when soil conditions are very favorable, but has
little ability to withstand hardship. Many of the present walnut groves
have been planted on soil which for one reason or another is not well
adapted to this root, and as a result the trees gradually fail as they
grow older.

Again, the inherent nature of the trees in regard to quality and
quantity of production is responsible to a considerable extent for the
present unsatisfactory condition. Almost every walnut tree over ten
years of age in Santa Barbara, Ventura, Los Angeles, and Orange
counties is of the type known as the Santa Barbara soft shell seedling.
These have all descended from a few trees of the original planting of
Joseph Sexton and have in most cases been planted with no discrimina-
tion or selection of the nuts. As a result of this the type has degener-
ated to a marked extent and a large proportion of the present trees are
decidedly inferior inheritently to their original parents.

In addition to all this, the climatic conditions of the last two or

Bulletin 218] CALIFORNIA PLANT DISEASES. 1181

three years have been such as to have a decidedly unfavorable effect
upon walnuts, as described in other portions of this bulletin. The case
is, therefore, not altogether hopeless, since it is to be expected that even
under present conditions we may have better walnut seasons and crops
than those of the past few years. With better and more regular cultural
care of the orchards which is now coming into practice, there is still more
hope for the future. Growers are beginning to realize that some of the
attention which they give their orange and lemon groves might not be
wasted upon walnuts.

The faults outlined above may be counteracted to a considerable ex-
tent by thinning out the closely planted trees, either by removing a por-
tion of the tops or taking out some of the trees bodily, and by giving
the groves cultivation, irrigation, and fertilization along rational lines.
The fact is apparent, however, that the present seedling walnut groves
have had their day and that they will gradually disappear just as the
seedling apple, the seedling orange and all other fruits of the same
nature are gradually supplanted by more desirable, definite varieties.
The real hope of the walnut industry lies in the future, and is based
upon an entirely new start along the lines just mentioned. Upon this
basis there is absolutely no doubt but that the walnut will again come
into its own and prove one of our most attractive and profitable crops.
A complete bulletin upon walnut culture in all of its phases is now
under preparation by the senior writer.

WATERMELON.

Wilt (Fusarium).
The vines wilt and die with a dry rot of the stem and leaves. Caused
by a fungus which infests the soil and lives there from year to year.
Plant on new soil. Resistant varieties are being developed.

WHEAT.

Closed Smut (Tilletia foetans). Figure 102.
The grains are converted into a black substance which does not scatter
out loosely as in the next. Affected grains have a disagreeable odor.
Use seed treatment as for barley smut.

Loose Smut (Ustilago tritici). Figure 102.

The kernels and chaff are converted into a black, powdery mass, which
blows away before harvest time, leaving the bare stalks.

Use the hot water treatment as for barley if this form of smut is
particularly bad.

Rust (Puccinia graminis).

The rust appears as an orange-red powder on the leaves, later turning
black. Wheat fields are sometimes badly injured when the weather is
10— Bul. 218

1182

UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

moist and favorable to the rust. Some varieties are considerably re-
sistant.

Yellow s — Wi n teri ng .

Wheat, as well as other grains, sometimes shows in the spring a yellow-
ing and discoloration of the leaves with no apparent specific cause.

Fig. 102. — Closed and loose smut of wheat (Tilletia foetans and

Ustilago tritici).

Sometimes the whole field shows this condition so decidedly as to have
the appearance of being badly injured. The trouble appears to be due
to climatic conditions, producing a disturbance in the growth of the
plant. The yellowing usually disappears in the spring and, if condi-
tions are favorable, the plants regain their normal appearance.

Bulletin 2183 CALIFORNIA PLANT DISEASES. 1183

FUNGICIDES.

The following are the chief substances used for the control of plant
diseases by spraying, dipping, disinfecting, etc. It should be clearly
understood that all control of this nature must be accomplished entirely
by prevention rather than cure. In other words, these fungicides
where they are to be effective must be applied for the purpose of poison-
ing and killing the spores or germs of the parasites and thus preventing
their further spread and development.

bluestone. (Copper Sulphate.)

This material comes in the form of large, hard, blue crystals, and is
used in large quantities in fungicidal work, as the basis of Bordeaux
mixture. The crystals dissolve readily in hot water and more slowly in
cold. If thrown into the water and allowed to sink to the bottom they
soon form there a concentrated solution and only a small part of the
material is dissolved. For this reason it is necessary to either stir the
water frequently or suspend the bluestone in a sack or basket so that
it just dips under the surface. This substance is extremely caustic to
vegetation when used alone, and is, therefore, commonly combined with
lime in Bordeaux mixture.

A plain solution of bluestone and water of about 3 pounds to 50 gal-
lons may be used during the winter time on fruit trees to remove moss,
etc., from the bark. This solution would be extremely disastrous to
green leaves.

LIME.

This material in the form called "quick-lime" or "stone-lime,' is
mainly useful in fungicidal work as an ingredient of Bordeaux mixture.
For this purpose it must be in a fresh, hard condition and not in the
least air-slaked.

Hydrated lime, a form which is coming considerably into use, consists
of lime which has been slaked with a small amount of water and then
ground to a fine powder. In this condition it can not air slake, but re-
tains its quality indefinitely. This form of lime is being used to some
extent for making Bordeaux mixture and quite extensively as a basis
of dust sprays.

sulphur.

This in a finely powdered condition is used extensively in the control
of plant diseases, particularly for surface mildews and the like. Sul-
phur acts in these cases through its gaseous fumes, which are produced
when the hot sun shines upon it. For such purposes the sulphur should
be in as finely divided a condition as possible and this is best obtained
in the form known as flowers of sulphur or sublimed sulphur. Ground

1184 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

sulphur is to be had in various degrees of fineness, but should never be
used for application to plants except in the very finest condition. The
sublimed form is somewhat more expensive per pound, but much bulkier,
and therefore no more expensive in the end. When used in liquid sprays
where cooking takes place and the sulphur becomes dissolved, the
cheaper, coarser forms may be used.

COPPER CARBONATE.

This material is used to a limited extent in the form of a solution in
ammonia and water in the case of spraying fruit, flowers, ornamentals,
etc., where Bordeaux mixture is objectionable on account of its disfigur-
ing effect. This ammoniacal copper carbonate is prepared in the follow-
ing manner :

Copper carbonate 6 ounces

Strong ammonia 3 pints

Water 50 gallons

Make a paste of the copper carbonate with a little water and add to
this the ammonia diluted with about two gallons of water. Stir vigor-
ously and continue to add the ammonia until all the copper is dissolved.
Then dilute to 50 gallons.

potassium sulphide. (Liver of Sulphur.)

This material comes in the form of a greenish-yellow solid. Used
particularly in a solution of 1 ounce to 3 gallons of water for the con-
trol of surface mildews. Both the solid and the solution deteriorate on
standing exposed to the air.

FORMALIN.

This is a clear liquid consisting of a gas dissolved in water. Commer-
cial formalin should have a strength of 40 per cent and the formula
given below is based upon this concentration. In buying formalin par-
ticular care should be taken to see that the material purchased is a
40 per cent solution. One pint dissolved in thirty gallons of water is
used for soaking seed potatoes in the control of scab and for grain in
controlling smut.

CORROSIVE SUBLIMATE.

This is a white, extremely poisonous, solid material which may be
bought most conveniently in the form of tablets. It is used particularly
for disinfection after cutting out pear blight, dissolved in water in a
strength of 1-1000. The tablets may be obtained in a size convenient for
making this strength. This material is particularly poisonous to ani-
mal life and should not be carelessly used.

Bulletin 218] CALIFORNIA PLANT DISEASES. 1185

BORDEAUX MIXTURE.

Copper sulphate (Milestone) 5 pounds

Quick-lime (good stone lime) 6 pounds

Water 50 gallons

Put the bluestone in a sack and hang so it will be suspended just
under the surface of a barrel of water over night, or dissolve in hot
water. Use one gallon of water to one pound of bluestone. Slake the
lime in a separate barrel, using just enough water to make a smooth,,
clean, thin whitewash. Stir this vigorously. Use wooden vessels only.

Fill the spray tank half full of water, add one gallon of bluestone
solution for each pound required, then strain in the lime and the
remainder of the water and stir the mixture thoroughly. Do not mix
the solution hot.

For extensive work, large amounts of bluestone and lime may be pre-
pared in advance in separate receptacles, making stock solutions of
definite strength. (One pound to the gallon is convenient.) Always
dilute well before mixing.

The formula may be varied according to conditions, using from 3 to
8 pounds of bluestone to 50 gallons of water and an equal amount or
slight excess of lime. Use the stronger mixture in rainy weather.
Keep the mixture constantly agitated while applying.

Recently, the so-called "hydrated" lime has been used to a con-
siderable extent in making Bordeaux. Chemically, the hydrated lime
is entirely satisfactory for making Bordeaux mixture, and it is some-
what more convenient for use than stone or quick lime. The same quan-
tities should be employed as with the latter. Objection has been made
to hydrated lime in some quarters on the ground that Bordeaux mixture
thus prepared settles more readily and has a coarser consistency. We
are not prepared to state, however, that this is a general fault of
hydrated-lime Bordeaux.

In using large quantities of Bordeaux mixture or any other fungicide
it is very convenient to place tanks upon an elevated platform to which
water is piped. The various solutions can then be prepared upon this
platform and discharged by gravity into a spray tank. In the case of
Bordeaux mixture it is advisable to run the diluted bluestone and lime
solution into a single trough and let them drop from this into a spray
tank, as in this way a more complete mixture is secured.

CAUSTIC SODA AND POTASH.

Either of these substances may be used for spraying dormant trees
in winter, dissolved in water in the proportion of 1 pound to 10 gallons.
This is effective in removing moss, lichens, etc., from trees and also has
some fungicidal value in certain cases. These materials are also used

1186 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

combined with sulphur in liquid sprays in which the sulphur goes into
solution.

SULPHUR SPRAYS.

Quick-lime 20 pounds

Ground sulphur 15 pounds

Water 50 gallons

Slake the lime with hot water in a large kettle, add the sulphur and
stir well together. After the violent slaking subsides add more water
and boil the mixture over a fire for at least one hour. After boiling
sufficiently strain into the spray tank and dilute with water to the
proper strength. If a steam boiler is available this mixture may be
prepared more easily on a large scale by cooking in barrels into which
steam pipes are introduced. This mixture can not be applied safely
except during the winter Avhen the trees are dormant.

SELF-BOILED LIME-SULPHUR.

The heat generated by the lime in slaking is in itself sufficient to
dissolve a considerable quantity of sulphur and a mixture may be pre-
pared in this way which is quite satisfactory for fungicidal purposes.
This method has been in use for several years in California, as described
in Bulletin 163 of the California Experiment Station. The lime is
placed in a tight cask instead of a kettle, and over it is poured the
sulphur mixed into a thin paste with hot water. Ten or fifteen gallons
of boiling water are then added and the cask covered tightly with sacks
and a wooden cover. Violent boiling immediately takes place. When
this begins to subside the mixture is stirred thoroughly and after the
boiling stops it is strained into the spray tank and diluted to the proper
strength.

Recently a more dilute form of this mixture has found considerable
use for fungicidal purposes for application to trees in foliage during
the summer time. This is made in a similar manner to that just de-
scribed, using 10 pounds of lime and 10 pounds of sulphur to 50 gallons
of water.

See Circular 27, Bureau of Plant Industry. U. S. D. A.

CONCENTRATED LIME-SULPHUR.

Another method of preparing the lime-sulphur spray is that described
in Bulletin 306, Geneva, New York Experiment Station.

Formula :

Lump lime 60 pounds

Sulphur 125 pounds

Water 50 gallons

This is mixed in a kettle and cooked over a fire, according to the first
method given above, boiling for one or more hours. After the cooking

Bulletin 2181 CALIFORNIA PLANT DISEASES. 1187

is completed the clear liquid is drawn off and strained and water added
sufficient to make the required 50 gallons. For use, 5 gallons of this
concentrated liquid is diluted with 45 gallons of water. This is said
to be safe to use on trees when the buds are opening or even in full
foliage.

COMMERCIAL LIME-SULPHUR.

Several commercial preparations of lime-sulphur are now on the
market which are similar in nature to the above. These are concentrated
mixtures to be used diluted with water. There is no reason why they
should not be effective for the purposes to which such a spray is
adapted if properly prepared.

OTHER LIQUID SULPHUR SPRAYS.

• Sprays somewhat similar to the above are sometimes made for
fungicidal purposes by boiling sulphur with caustic soda or potash solu-
tion. The following formula is a typical one :

Caustic soda 12 pounds

Sulphur 50 pounds

Water 200 gallons

Bring the soda to a boil in a kettle of water, then add the sulphur
slowly and boil with frequent stirring for about an hour. Strain the
mixture into the spray tank and make up to 200 gallons. Caustic potash
may be used instead of soda.

IRON SULPHIDE SPRAY.

This is highly recommended by Mr. W. H. Volck, County Entomolo-
gist of Santa Cruz County, as a fungicide for the control of apple mil-
dew. The process of preparing this material is quite complicated and
is one which would scarcely be undertaken by the average grower. A
commercial preparation of this material is on the market.

ADHESIVES.

In spraying plants with a smooth or waxy surface, such as onions,
cabbage, and asparagus, it is sometimes useful to add to Bordeaux mix-
ture or other sprays some material which will make the spray liquid
adhere more satisfactorily. The following formula is useful for this
purpose :

Resin 2 pounds

Sal soda crystals 1 pound

Water 1 gallon

Boil in a kettle until the mixture becomes a clear, amber liquid. Add
this amount to 50 gallons of spray.

1188 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION.

SOAP.

The addition of 4 or 5 pounds of whale-oil or other cheap soap to
each 50 gallons of Bordeaux or other spray is quite effective in increas-
ing its adhesive qualities.

LITERATURE.

A few references to some of the best books upon the subjects treated
in this bulletin may be of use to those who wish to obtain more detailed
information along various lines. The following list is given as being
well adapted to the general reader :

"Fungous Diseases of Plants." Dug-gar. Published by Ginn & Company.

"Diseases of Economic Plants." Stevens & Hall. Published by The Macmillan
Company.

"Diseases of Plants." Tubeuf & Smith. Published by Longmans & Company.

"Disease in Plants." Marshall Ward. Published by Macmillan & Company.

"Text Book of Botany," 2 volumes. Coulter, Barnes & Cowles. Published by
The American Book Company.

"California Fruits." Wickson. Published by Pacific Rural Press Company.

"Soils." Hilgard. Published by The Macmillan Company.

INDEX.

Acid soil 1066.

Adhesives 1187.

Air — relation to plant growth 1047.

Alfalfa.

crown gall 1079; dodder 1083; leaf spot
1079; rust 1079; stem rot 1081.

Almond.

crown gall 1084; die back 1086; fruit

drop 1084; oak fungus, root rot 1084;

rust 1084; shot-hole 1083; sour sap

1085.
Anaheim disease.

grape 1117.

Apple.

blight 1089; climatic effects 1093; club
tip 1093; storage spot 1092; die back,
see Almond; fruit spot 1092; hollow
1093; little leaf 1093; mildew 1088;
root rot 1089; scab 1089; seasonal
effects 1093; stem rot 1089; sunburn
1091; toadstool disease 1089.

Apricot.

blossom rot 1097; brown rot 1097; bud
blight 1096; climatic effects 1098;
crown gall, die back, fruit drop, see
Almond; fruit spot 1095; gummosis,
see Cherry; root rot, see Almond;
scab 1097; seasonal effects 1098; shot-
hole 1095; sour sap 1098.

Asparagus.

rust 1100.

Aster.

yellows 1101.
Atmospheric effects, injurious 1051.
Bacteria, general acount of, 1078.
Bacteriosis.

walnut 1172.
Barley.

leaf spot 1102; smut, closed and loose

1101.

Bean.

mildew 1102; rust 1102; spot 1102.
Beet.

blight 1104; curly top 1104; downy

mildew 1103; eutettix 1104; leaf spot

1102; nematode 1104; root knot 1104;

root rot 1104; rust 1102.
Black knot.

grape 1115; quince 1160; walnut 1178.
Black leaf.

pear 1155.
Black leg.

potato 1158.

Black rot.

cabbage 1108; orange 1143; sweet
potato 1167.

Black spot,
rose 1163.

Blackberry.

crown gall 1107; leaf spot 1107; rust
1107; soft rot 1107.

Blasting — to loosen soil 1074.

Blight.

apple 1094; apricot bud blight 1089;
beet 1104; celery 1108; lemon 1126;
loquat 1130; orange, see Lemon; pea
1149; peach 1149; pear 1154; potato,
early blight, 1157; late blight 1157;
quince, see Pear; rose, cane blight
1163; sycamore 1167; tomato, summer
blight 1168; winter blight 1168; walnut.
1172.

Blosom end rot.

tomato 1168.

Blossom rot.

apricot 1097.

Blue mold.

lemon 1126; orange 1142.

Bluestone 1183.

Boll rot.

cotton 1111.

Bordeaux mixture 1185.

Brown rot.

apricot 1097; cherry 1109; lemon 1122;
orange, see Lemon; peach and plum,
see Apricot.

Brown spot.

orange 1143.

Brown streak.

potato 1158.

Brunissure.

grape 1118.

Bud blight.

apricot 1096.

Cabbage.

black rot 1108; club foot 1108.

California yellows.
peach 1151.

Cane blight,
rose 1163.

Carnation.

leaf spot 1108; rust 1108; stem rot.
1108; wilt 1108.

1190

INDEX.

Chemical elements.

deficiency in the soil 1061.

Celery.

root rot 1109; stem rot 1109; summer
blight 1108; winter blight 1108.

Cement dust 1060.

Cherry.

brown rot 1109; die back 1110; fruit
drop 1110; guramosis 1109; root rot
1109.

Chlorosis.

orange 1137.

Chrysanthemum,
rust 1110.

Citrus.

diseases, see Lemon and Orange;
peculiarities 1133.

Climatic conditions.

irregular 1054; relation to plant 1048.

Climatic effects.

apple 1093; apricot 1098.

Club foot.

cabbage 1108.

Club tip.

apple 1093.

Cold 1051.

Cold storage spot,
apple 1092.

Copper carbonate 1184.

Copper sulphate 1183.

Corn.

mold 1111; rust 1111; smut 1110.

Corrosive sublimate 1184.

Cotton.

boll rot 1111.

Cottony mold.

lemon 1123.

Coulure.

grape 1117.
Crater blight.

pear 1156.
Crop production, ideal conditions for, 1041.

Crown gall.

almond 1084; apricot, see Almond;
eucalyptus 1114; nursery stock 1131;
peach and plum, see Almond; walnut
1178.

Cucumber.

leaf spot 1112; mildew 1111; root knot
1112; stem rot 1111.

Curly bark,
pear 1156.

Curly top.
beet 1104.

Currant.

mildew 1112.

Dahlia.

mildew 1112.

Damping off.

eucalyptus 1113; lettuce 1130; tomato

1167.
Dewberry, see Blackbery.

Die back.

almond 1086; apple and apricot, see
Almond; cherry 1110; orange, Florida
die back 1136, 1139; peach and plum,
see Almond; walnut 1176.

Disease.

defined 1039; causes classified 1049.

Dodder.

alfalfa 1083.

Downy mildew.

beet 1103; onion 1133.

Drop.

lettuce 1130.

Dry rot.

olive 1133; potato 1156.

Dryness.

Atmospheric, injurious effects of

1055; soil 1067.
Dust 1060.
Early blight.

potato 1157.

Egg plant.

rot 1112; stem rot, wilt 1113.

Erinose.

walnut 1176.

Eucalyptus.

crown gall 1114; damping off 1113;
leaf spot 1113; mildew 1113.

Eutettix.

beet 1104.

Exanthema.

orange 1136.

Fertilization, soil 1062.

Florida die-back.

orange 1136.
Fluids — movements in plants 1046.

Folletage.

grape 1118.

Formalin 1184.

Frizzles.

pecan 1156.

Frost 1051.

protection 1052.

Fruit drop.

almond 1084; apricot, see Almond;
cherry 1110; peach, see Almond; pear
1156.

Fruit gumming,
peach 1151.
Fruit spot.

apple 1092; apricot 1095.
Fungi, general account of, 1077.
Fungicides 1183.
Gas, illuminating — injury to trees 1075.

INDEX.

1191

Gopher 1075.

Grape.

Anaheim disease 1117; black knot
1115; brunissure 1118; coulure 1117;
folletage 1118; little leaf 1117; mildew
1114; red leaf 1118; rougeot 1118.

Grape fruit, see Orange.

Grey mold.

lemon 1125.

Guava.

russeting 1119.

Gummosis.

apricot, see Cherry; cherry 1109;
lemon 1120; orange, see Lemon.

Hail 1057.

Hardpan 1072.
blasting 1074.

Heat, atmospheric, injurious effects of,
1053.

Hollyhock.

rust 1119.

Hollow.

apple 1093.

Insects 1076.

Introduction 1039.

Iris.

leaf spot 1120.

Iron sulphide 1187.
Late blight,
potato 115 f.

Leaf.

functions of 1047; respiration in 1048.

Leaf curl.

peach llii).

Leaf gum spot,
orange 1142.

Leaf spot.

alfalfa 1079; barley 1102; beet 1102;
blackberry 1107; carnation 1108; cu-
cumber 1112; eucalyptus 1113; iris
1120; madrone 1130; oleander 1131;
olive 1133; palm, date 1148; palm,
Washingtonia 1148; strawberry 1166;
tomato 1171; vetch 1171.
Lemon.

blue and green mold, see Orange
brown rot 1122; cottony mold 1123
gray mold 1125; gummosis 1120
peteca 1129; red rot 1129; twig blight
1126; wither- tip, "tear stain" 1127.

Lettuce.

damping off 1130; drop 1130.

Lime 1183.

Lime-sulphur 1186, 1187.

Literature 1188.

Little leaf.

apple 1093; grape 1117; peach 1151;
quince, see Peach.

Little peach 1050.

Little potato 1158.

Loganberry, see Blackberry.

Loquat.

blight 1130; scab 1130.

Madrone.

leaf spot 1130.

Mai di gomma.
orange 1136.

Mildew.

apple 1088; bean 1102; beet, downy
mildew 1103; cucumber 1111; currant
1112; dahlia 1112; eucalyptus 1113;
grape 1114; onion, downy mildew
1133; pea 1149; peach 1150; pumpkin
1160; rose 1163; strawberry 1166; syca-
more 1167.

Moisture.

atmospheric, injurious effects of, 1055;
excessive, in soil, 1071.

Mold.

corn 1111; lemon, grey mold 1125;
blue mold, see Orange; orange, blue
mold 1142.

Moles 1075.

Mottled leaf.

orange 1137.
Navel rot.

orange 1143.
Nematode.

beet 1104; nursery stock 1131; tomato

1171.

Nematode worm 1076.

Nursery stock.

crown gall 1131; nematode 1131; root
knot 1131.

Oak fungus.

almond 1084.

Oat.

rust 1131; smut 1131.

Oleander.

leaf spot 1131; twig gall 1131.

Olive.

dry rot 1133; leaf spot 1133; root rot
and toadstool, see Almond; tubercu-
losis. 1132.

Onion.

downy mildew 1133.

Orange.

anthracnose 1140; black rot 1143; blue
mold 1142; brown rot, see Lemon;
brown spot 1143; chlorosis 1137;
damping off 1141; die back 1139; ex-
anthema 1136; Florida die back 1136;
gummosis, see Lemon; leaf gum spot
1142; mal di gomma 1136; miscellane-
ous spots 1146; mottled leaf 1137;
navel rot 1143; puffing 1146; root rot
1140; scaly bark 1135; shoulder spot
1146; stain 1146; stem end spot 1146;
splitting 1145; tear stain 1140; toad-
stool 1140; trunk rot 1140; twig blight,
see Lemon; wither-tip 1140.

1192

INDEX.

Palm, date.

leaf spot 1148.

Palm, Washingtonia.
leaf spot 1148.

Pea.

blight 1149; mildew 1149.

Peach.

blight 1149; brown rot, see Apricot
California yellows 1151; crown gall,
die back, fruit rot, see Almond; fruit
gumming 1151; gummosis, see Cherry;
leaf curl 1149; little leaf 1151; little
peach 1150; mildew 1150; root rot,
rust, sour sap, see Almond; split pit
1151; yellows 1151.

Pear.

black leaf 1155; blight 1154; crater
blight 1156; curly bark 1156; fruit
drop 1156; ringed fruit 1156; scab 1153.

Pecan.

rosette or frizzles 1156.

Perforation.

walnut 1175.

Peteca.

lemon 1129.

Photosynthesis 1048.

Physiological diseases 1055.

Plant.

disease, causes classified 1049; disease
defined 1039; disease, directions for
examining 1049; food, substances taken
from soil 1043; growth, factors af-
fecting 1040; movement of fluids in
1046; pathology, scope 1040; physiol-
ogical diseases 1055; physiology 1041;
starch formation in 1048; sugar for-
mation in 1048.

Plum.

brown rot, see Apricot; crown gall,
die back, rust, sour sap, see Almond.

Pomelo, see Orange.

Potash, caustic 1185.

Potassium sulphide — liver of sulphur 1184.

Potato.

black leg 1158; brown streak 1158;
dry rot 1158; early blight 1157; gen-
eral directions for planting 1159; late
blight 1157; little potato 1158; scab
1157.

Pumpkin.

mildew 1160; wilt 1160.

Prune.

shrivels 1160; see Plum, also.

Puffing.

orange 1146.

Quince.

black knot 1160; blight, see Pear; lit-
tle leaf, see Peach.

Rabbits 1075.

Red leaf.

grape 1118.

Red rot.

lemon 1129.

Resin 1188.

Respiration.

in leaves 1047; in root 1044.

Ringed fruit,
pear 1156.

Root.

functions of 1044; respiration in 1044,

Root knot.

beet 1104; cucumber 1112; nursery
stock 1131; peach, see Almond crown
gall; tomato 1171.

Koot rot.

almond 1084; apple 1089; apricot, see
Almond; celery 1109; cherry 1109;
olive 1133; orange 1140.

Rose.

black spot 1163; cane blight 1163; mil-
dew 1163; rust 1163.

Rosette.

pecan 1156.

Rot.

egg plant 1112.
Rougeot.

grape 1118.

Russeting.

guava 1119.

Rust.

alfalfa 1079; almond 1084; asparagus
1100; bean 1102; beet 1102; black-
berry 1107; carnation 1108; chrysan-
themums 1110; corn 1111; hollyhock
1119; oat 1131; peach and plum, see
Almond; rose 1163; wheat 1182.

Saline water, irrigation with, 1065.

Santa Ana 1053.

Scab.

apple 1089; apricot 1097; loquat 1130;
pear 1153; potato 1157.

Scaly bark,
orange 1135.

Seasonal effects.

apple 1093; apricot 1098.

Shot hole.

almond 1083; apricot 1095.

Shoulder spot,
orange 1146.

Shrivels.

prune 1160.

Slime molds 1079.

Slugs 1076.

Smelter fumes 1058.

Smut.

barley 1101; corn 1110; oat 1131; sor-
ghum 1166; wheat 1182.

INDEX.

1193

Soap, 1188.

Soda, caustic 1185.

Soft rot.

blackberry 1107; sweet potato 1167.

Soil.

acid 1066; alkali 1063; artificial sub-
stances in 1074; chemical deficiency
1061; chemical nature 1045; chemical,
physical and biological relation to
plant growth 1043; deficiencies 1061;
dryness 1067; excess of water 1071;
faulty structure 1072; fertilization
1062; water deficiency 1061, 1067.

Sorghum.

smut 1166.

Sour sap.

almond 1085; apricot 1098; peach and
plum, see Almond.

Split pit.

peach 1151.

Splitting.

orange 1145.
Spot.

bean 1102; orange, leaf gum spot
1142; miscellaneous spots, shoulder
spot, stem end spot 1146.

Squash, see Pumpkin.

Squirrels 1075.

Stain.

orange 1146.

Starch — formation in plant 1048.

Stem end spot.

orange 1146.
Stem rot.

alfalfa 1081; apple 1089; carnation

1108; celery 1109; cucumber 1111; egg

plant 1113; tomato 1170.

Strawberry.

leaf spot 1166; mildew 1166.

Subsoil, dry 1069.

Subsoil, faulty structure 1072.

Sugar, formation in plant 1048.

Sulphur 1183.
sprays 1186.

Summer blight.

celery 1108; tomato 1168.

Sunburn 1053.

apple 1091; prevention of 1054; wal-
nut 1175.

Sunscald 1053.
Sweet potato.

black rot 1167; stem rot 1167; soft

rot 1167; wilt 1167.

Sycamore.

blight 1167; mildew 1167.

Toadstool disease.

almond, see Root rot 1084; apple 1089;
olive, see Almond; orange 1140.

Tomato.

blossom end rot 1168; damping off
1167; leaf spot 1171; nematode 1171;
root knot 1171; stem rot 1170; summer
blight 1168; winter blight 1168.

Trunk rot.

orange 1140; walnut 1173.

Tuberculosis,
olive 1132.

Turnip, see Cabbage.

Twig blight.

lemon 1126; orange, see Lemon.

Twig gall.

oleander 1131.

Vetch.

leaf spot 1171.

Walnut.

bacteriosis 1172; black knot 1178;
blight 1172; crop failure 1179; crown
gall 1178; die back 1176; erinose 1176;
perforation 1175; sunburn 1175; trunk
rot 1173; yellows 1178.

Water.

alkali, irrigation with 1064; alkali,
rise of, in soil water 1065; deficiency
in soil 1061, 1067; excessive, in soil
1071; fluctuating level in soil 1071;
saline, irrigation with 1065.

Watermelon,
wilt 1181.

Wheat.

closed smut 1181; loose smut 1181;
rust 1181; yellows 1182.

White rot.

lemon 1123.

Wilt.

carnation 1108; egg plant 1113; pump-
kin 1160; watermelon 1181.

Wind, injurious effects of, 1056.
Wind-breaks 1057.
Winter blight.

celery 1108; tomato 1168.

Wither-tip.

lemon 1127; orange 1140.

Worm, Nematode 1089.

Yellows.

aster 1101; peach, California yellows
1151; walnut 1178; wheat 1182.

STATION PUBLICATIONS AVAILABLE FOR DISTRIBUTION.

REPORTS.

1896. Report of the Viticultural Work during the seasons 1887-93, with data regard-

ing the Vintages of 1894-95.

1897. Resistant Vines, their Selection, Adaptation, and Grafting. Appendix to Viti-

cultural Report for 1896.

1902. Report of the Agricultural Experiment Station for 1898-1901.

1903. Report of the Agricultural Experiment Station for 1901-03.

1904. Twenty-second Report of the Agricultural Experiment Station for 1903-04.

BULLETINS.

Reprint. Endurance of Drought in Soils

of the Arid Region.
No. 128. Nature, Value, and Utilization
of Alkali Lands, and Tolerance
of Alkali. (Revised and Re-
print, 1905.)

133. Tolerance of Alkali by Various
Cultures.

147. Culture Work of the Sub-sta-
tions.

149. California Sugar Industry.

151. Arsenical Insecticides.

153. Spraying with Distillates.

159. Contribution to the Study of
Fermentation.

162. Commercial Fertilizers. (De-
cember 1, 1904.)

165. Asparagus and Asparagus Rust
in California.

167. Manufacture of Dry Wines in

Hot Countries.

168. Observations on Some Vine Dis-
eases in Sonoma County.

169. Tolerance of the Sugar Beet for

Alkali.

170. Studies in Grasshopper Control.

171. Commercial Fertilizers. (June

30, 1905.)

172. Further Experience in Asparagus

Rust Control.
174. A New Wine-cooling Machine.

176. Sugar Beets in the San Joaquin

Valley.

177. A New Method of Making Dry

Red Wine.

178. Mosquito Control.

179. Commercial Fertilizers. (June,

1906.)

180. Resistant Vineyards.

181. The Selection of Seed-Wheat.

182. Analysis of Paris Green and

Lead Arsenic. Proposed Insec-
ticide Law.

183. The California Tussock-moth.

184. Report of the Plant Pathologist

to July 1, 1906.

185. Report of Progress in Cereal

Investigations.

186. The Oidium of the Vine.

187. Commercial Fertilizers. (Janu-

ary, 1907.)

No. 188.

189.

190.
191.
192.

193.

194.

195.

197.

198.
199.
200.

201.

202.

203.

204.

205.

206.

207.

208.
209.
210.

211.

212.
213.
214.
215.

216.
217.

Lining of Ditches and Reservoirs
to Prevent Seepage and Losses.

Commercial Fertilizers. (June,
1907.)

The Brown Rot of the Lemon.

California Peach Blight.

Insects Injurious to the Vine in
California.

The Best Wine Grapes for Cali-
fornia ; Pruning Young Vines ;
Pruning the Sultanina.

Commercial Fertilizers. (De-
cember, 1907.)

The California Grape Root-worm.

Grape Culture in California ;
Improved Methods of Wine-
making ; Yeast from California
Grapes.

The Grape Leaf-Hopper.

Bovine Tuberculosis.

Gum Diseases of Citrus Tres in
California.

Commercial Fertilizers. (June,
1908.)

Commercial Fertilizers. (De-
cember, 1908.)

Report of the Plant Pathologist
to July 1, 1909.

The Dairy Cow's Record and the
Stable.

Commercial Fertilizers. (De-
cember, 1909.)

Commercial Fertilizers. (June,
1910.)

The Control of the Argentine
Ant.

The Late Blight of Celery.

The Cream Supply.

Imperial Valley Settlers' Crop
Manual.

How to Increase the Yield of
Wheat in California.

California White Wheats.

The Principles of Wine-Making.

Citrus Fruit Insects.

The Housefly in Its Relation to
Public Health.

A Progress Report Upon Soil and
Climatic Factors in Influencing
the Composition of Wheat.

Honey Plants of California.

CIRCULARS.

No. 1. Texas Fever.

5. Contagious Abortion in Cows.
7. Remedies for Insects.
9. Asparagus Rust.

11. Fumigation Practice.

12. Silk Culture.

15. Recent Problems in Agriculture.
What a University Farm is For.
19. Disinfection of Stables.
29. Preliminary Announcement Con-
cerning Instruction in Practical
Agriculture upon the University
Farm, Davis, Cal.
White Fly in California.
White Fly Eradication.
33. Packing Prunes in Cans. Cane
Sugar vs. Beet Sugar.
Analyses of Fertilizers for Con-
sumers.
Instruction in Practical Agricul-
ture at the University Farm.
Suggestions for Garden Work in
California Schools.

47. Agriculture in the High Schools.

48. Butter Scoring Contest, 1909.

49. Insecticides.

50. Fumigation Scheduling.

30
32

36.

39.

46.

No. 51. University Farm School.

52. Information for Students Concern-

ing the College of Agriculture.

53. Announcement of Farmers' Short

Courses for 1910.

54. Some Creamery Problems and

Tests.

55. Farmers' Institutes and Universit

Extension in Agriculture.

57. Announcement of Farmers' Short

Courses in Animal Industry and
Veterinary Science.

58. Experiments with Plants and Soils

in Laboratory, Garden, and
Field.

59. Tree Growing in the Public

Schools.

60. Butter Scoring Contest, 1910.

61. University Farm School.

62. The School Garden in the Course

of Study.

63. How to Make an Observation

Hive.

64. Announcement of Farmers' Short

Courses for 1911.

65. Calif ornin. Insecticide Law.

66. Insecticides and Insect Control.