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Bulletin 45

Hay, 1897

NEW HAMPSHIRE COLLEGE

AGRICULTURAL EXPERIMENT STATION

FRUIT AND POTATO DISEASES

SPOT DISEASE OF APPLE

BY H. H. LAMSON

NEW HAMPSHIRE COLLEGE

OF

AGRICULTURE AND THP: MECHANIC ARTS

DURHAM

NEW HAMPSHIRE COLLEGE

OF

AGRICULTUEE AND THE MECHANIC ARTS

AGRICULTURAL EXPERIMENT STATION

Durham, N. H.

BOARD OF CONTROL

Hon. GEO. A. WASON, Chnirman, New Boston.
Pres. CHAS. S. MUEKLAND, ex officio, Durham.
CHARLES W. STONE, A. M., Secretary, Andover.
Hon. JOHN G. TALLANT, Pembroke.
Hon. frank JONES, Portsmouth.

THE STATION COUNCIL

Pres. CHAS. S. MURKLAND, A. M., Ph. D., Acting Director.
FRED W. MORSE, B. S., Vice-Director and Chemist.
FRANK WM. RANE, B. Agr., M. S., Agriculturist and Horti-
culturist.
CHAS. H. PETTEE, A. M., C. E., Meteorologist.
HERBERT H. LAMSON, M. D., Bacteriologist.
CLARENCE M. WEED, D. Sc, Entomologist.

ASSISTANTS.

LEIGH HUNT, B. S., Assistant Agriculturist and Horticul-
turist.
CHARLES D. HOWARD, B. S., Assistant Chemist.
WILLIAM F. FISKE, Assistant Entomologist.
CLEMENT S. MORRIS, Clerk.

The Bulletins of this Station are sent free to anj- resident of New Hamp-
shire upon application.

Experiments in the Treatment of Fungous
Diseases of Fruit and Potatoes

BY H. H. LAMSON

The diseases with which this Bulletin is concerned are those
known as fungous diseases. They are not due to insects,
which belong to the animal kingdom, but to members of the
vegetable kingdom — that is to say, plants. These disease-pro-
ducing plants belong to the class known as fungi, and as they
grow upon other plants, they are called parasitic fungi. They
are so small that their nature cannot be made out by the naked
eye, so that it is not strange that they are not so well under-
stood by the majority of people as are insects. The parasitic
fungi grow at the expense of the plant on which they live, and
cause, in many cases, serious damage; and in the case of cul-
tivated plants, great pecuniary loss. It has been found that
many of these diseases may be largely prevented by spraying
with some substance which is harmless to the cultivated, but
.poisonous to the fungous, plant.

DISEASES OF THE APPLE AND PEAR

The most serious fungous disease of the apple and pear is
usually the scab. This disease appears on both the fruit and
the foliage. On the fruit it appeals as dark gteen or almost
black spots, with a velvety surface. The spots are circular in
outline, and occur separately or run together in irregular
patches, often covering a large portion of the surface. The
spots are thickened, and slightly raised above the surface, so
that the term scab is very applicable to the disease.

A fruit which is badly affected with the scab is usually
deformed or one-sided, and frequently cracked so as to be
worthless. Certain varieties of both apples and pears are more

46 FRUIT AND POTATO DISEASES

liable to be attacked by this disease than others. Upon the
foliage the scab appears as black or dusky irregular patches
upon the upper surface of the leaf. The scab is caused by a
parasitic fungous plant, which finds its proper soil on the
fruit or leaf. The disease is spread by spores which develop
on the surface of the scab spots.

The amount of damage done by the scab varies from year to
year. In some years it is very prevalent, while in others it
does comparatively little injury.

The scab is one of the diseases which can be most effectually
prevented by spraying with a fungicide such as the Bordeaux
mixture.

During the last three years the Baldwin apple, which is very
largely grown in southern New Hampshire, has been badly
affected by another fungous disease entirely different from the
scab. This disease is characterized by the appearance on the
surface of the apple of numerous small brown spots, varying in
diameter from a sixteenth to an eighth of an inch (see cover).
The spots are slightly sunken or depressed, so that the surface
lias a pitted appearance. They suggest the beginning of rot,
but they do not seem to increase in size ordinarily, thougli,
occasionally they do. They do not affect the tissues of the
apple deeply, and the principal damage done by the disease
seems to be the disfigurement of the fruit, which is often
great, rendering an otherwise perfect apple a second.

The following experiments show the effect on this disease
of spraying with Bordeaux mixture.

Experiment I. — Season of 1S95, on Baldwin apples:

A plot of trees A was sprayed four times with i to 10 Bor-
deaux mixture (i to 8, i to 10, i to 12 Bordeaux mixture mean
that I pound of blue vitriol was used for every S, 10, or 12 gal-
lons of water), twice before blossoming, May 4 and 10, and
twice after blossoming, Ma}^ 28 and June 14.

A plot of trees B was sprayed with i to 10 mixture once be-
fore, May 10, and twice after blossoming. May 28 and June 14.

A plot of trees C was sprayed with i to 8 mixture three,
times. May 10, 28, and June 14.

A plot of trees D was sprayed with i to 1 2 mixture three
times, May 11, 29, and June 15.

APPLE SCAB

47

At the first spraying after the blossoms had fallen, May 28,
4 onnces of Paris green were added to each 50 gallons of Bor-
deaux mixture for the codling-moth. This experiment is there-
fore a good illustration of a combined treatment for fungi and
insects.

The apples, when gathered, showed the following results :
Apples from unsprayed check trees, as well as from the
isprayed trees, were examined one by one and counted. The
first table compares the total number of apples unsprayed and
fepl'ayed.

Free from spots and worms
.Spotted ....
Wormy ....

Unsprayed.

Sprayed.

19 per cent.

82 per cent.

55 "

3 "

58 "

15 "

Of the unsprayed, 91/3 per cent, were graded as No. I's.
Of the sprayed, 53 per cent, were graded as No. I's.

The following table compares the effects of the different modes
of treatment of the sprayed trees on the spot disease :

Plot A. Plot B. Plot c. Plot D.

Free from spots . 95 per cent. 99 per cent. 96 per cent. 99 per cent-

These results show the efficiency of the Bordeaux mixture
in preventing the disease, with but little difference between the
different strengths and times of applying it.

Experiment II. — Season of 1S96, on Baldwin apples:

Plot I. Trees sprayed twice with i to 10 Bordeaux mixture,
once before blossoming and once after.

Plot 2. Trees sprayed with i to 10 Bordeaux mixture once
after blossoming.

vCheck trees unsprayed.

'Result :

Free from spots
.Spotted .

Unsprayed. Sprayed.

Plot 1. Plot 2.

32 per cent. 90 per cent. 82 per cent.
68 " 10 " 18 "

This shows a slight gain in favor of the trees sprayed twice.
In 1896 another disease was very prevalent on apples, and
-.together with the spot disease rendered much of the crop verv

48 . FRUIT AND POTATO DISEASES

unsightly. This disease is characterized by dirty or sooty'spots
on the skin of the apple. Tiie spots are roundish in outline;
varying much in size, they often run together, covering nearly
or quite the whole surface of the fruit. If drops of water con-
taining soot or lampblack were allowed to evaporate on the
surface of the apple, they would produce an appearance resem-
bling this disease. Its fungous nature, however, is clearly
revealed by the microscope. It is entirely superficial and, as
in case of the spot disease, the principal damage produced by
it is disfigurement. This disease is frequently observed on
Greenings and Northern Spies, but in 1S96 it attacked_many
other varieties, among them the Baldwin.

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I'm. 2. — Apple affected with sooty disease.

The sooty disease frequently attacks pears ; it is especially
bad on Beurre de Anjou and Lawrence. In case of the latter,
the favorable etiect of spraying with Bordeaux mixture has
been reported on in a previous Bulletin of this station (No. 27).

In 1S96, although no exact count was made, it is safe to say
that the sprayed apples showed 75 per cent, less of the disease
than the unsprnyed.

BLACK KNOT OF PLUM

It is probable that plums might be raised with profit in many
parts of New Hampshire, if it were not for the disease known
as black knot. Until recently it has been thought that the only

BLACK KNOT 49

efficient remedy for it was to cut oft' and burn the knots, but
from experiments at several stations, it seems probable that the
disease may be controlled by spraying with a fungicide. In
order that the spraying may be effective, it is necessary to
know something of its life history. Black knot is caused by
a fungous plant which grows in the inner bark of the tree,
causing it to swell and crack open. The fungous plant repro-
duces itself b}' means of spores, of which there are two princi-
pal kinds. One kind is known as the summer spore, and the
other as the winter spore.

The summer spores are formed soon after the bark cracks
open in the spring, in May or June, and serve to spread the
disease at that time. After this form of spore has disappeared,
a change takes place in the young knot, in which it assumes
its well-known appearance of a black swelling on the twigs or
branches. The surface of the black swelling is now thickly
studded with minute pimple-like projections, in the interior of
which are produced the winter spores. This form of spore is
mature and capable of germination in February or March
and serves to spread the disease early in the spring, when the
leaves and young shoots are making their appearance.

The spraying against this disease should be done at such a
time as will bring the fungicide in contact with the spores be-
fore they have time to germinate and infect the t'ees. Hence
it is recommended that the trees be sprayed early, before
growth begins, and again when the buds are ready to burst.
These sprayings are to destroy the winter spores. To destroy
the summer spores, the trees should be sprayed about the last
of May, and again about the middle of June. The best fungi-
cide for this purpose is the Bordeaux mixture. If this treat-
ment is faithfully followed, it is probable that the disease will,
to a large extent, be prevented. If spraying is not done, the
trees should be carefully examined in the spring and fall, when
the leaves are ofi', for knots or swellings ; these, when found,
should be removed and burned. Where large wounds are
made by this pruning, they should be covered with paint of
some kind.

It would be well if there were a law in New Hampshire,
properly enforced, compelling each fruit grower to keep his

FRUIT AND POTATO DISEASES

trees free from the black knot. The wild clierries are affected
with the same disease, and must be attended to if the disease
is to be stamped out.

DISEASES OF THE POTATO

The potato is subiect to three serious diseases, viz., the early
blight^ the late blight, and the scab, all caused by parasitic
plants or fungi. As their names indicate, the two blights, or
rusts, as they are frequently called, differ in their time of ap-
pearance. The early blight may appear in June upon early
potatoes. Upon late potatoes it does not appear usually before
the middle or last of July. The late blight appears about the
first of August. Besides this difference in time of attack, the two
diseases possess distinct characteristics, which may be readily
made out by any one on a careful examination of the affected
vines. The early blight produces dark brown, sharply defined
spots upon the leaves, which increase in number and size until
the whole leaf may be destroyed. This disease does not attack
the tubers. The late blight is characterized by the rapid with-
ering and death of the leav'es, without the appearance of sharply
defined spots. It usually begins at the margins, and soon
involves the whole leaf. Upon the under side of the leaves,
along the line separating the dead from the living portion, may
be observed a whitish, mold-like growth, which the microscope
shows to consist of the spore stalks of the fungus plant which
is causing the trouble. This white mold, the absence of well-
defined spots, and the rapid dying of the leaves, serve to distin-
guish the late blight from the early. We frequently find vines
aftected with both diseases at the same time. The blights can
be successfully treated by spraying.

The following are results obtained in treating potatoes for
early blight :

Sprayed four times with i to lo Bordeaux mixture

Unsprayed adjacent plot

Sprayed twice witii i to lo Bordeaux .

Unsprayed adjacent plot

Sprayed three times with i to lo Bordeaux .

Unsprayed adjacent plot

Sprayed three times with i to lo Bordeaux .
Unsprayed adjacent plot

Bushels

Gain from

per acre.

spraying.

237

. 185

52 bushels

352

. 287

65 "

337

255

82 "

320

246

74 "

POTATO SCAB 5 1

These results fairly represent the value of spraying, but as
the depredations of the fungous diseases vary so much from
year to year, and with other varying conditions, more favor-
able as well as less favorable ones may be obtained.

The scab of potatoes is caused by an organism which, while
of a vegetable nature, ditiers considerably from those causing
the blights. The scab of the potato has no similarity or rela-
tion to the above-described scab of the apple. The appearance
of scabby potatoes needs no description. The organisms caus-
ing the disease ma}- be present in the soil or upon the seed
used. It has been found that certain forms of fertilizers, while
they do not cause the disease, produce a condition of the soil
which is especially fivorable for its development. These fer-
tilizers are stable manure, ashes, and lime or plaster.

Treatment of the scab. If possible, seed free from scab
should be planted, but under ordinary conditions it is difficult
to be certain that the seed is wholly uncontaminated. Potatoes
should not be planted a second time on soil which has pre-
viously produced a scabby crop. The use of the above-
mentioned fertilizers should be avoided. Seed may be freed
from all or most of the germs by soaking in a solution of corro-
sive sublimate. This treatment may be carried out in the fol-
lowing way : Dissolve corrosive sublimate in water at the rate
of one ounce to eight gallons of water. Keep this solution in
a wooden vessel ; a barrel, half barrel, or wash-tub will answer
the purpose. Put the potatoes to be treated in a coarse sack-
ing bag, and plunge in the solution ; let them remain for an
hour and a half, moving them about occasionally to insure
thorough wetting ; then dry the potatoes, and they are ready
for planting. Care should be taken that they do not become
contaminated again by dirt from untreated potatoes. It should
be remembered that corrosive sublimate is a violent poison if
taken internally, therefore care should be taken in using it.

In 1S95 the following experiment was made, to ascertain the

effect of different fertilizers on the development of the scab :

Four plots of 4 rows each were planted.

Plot I was fertilized with commercial fertilizer.
Plot 3 was fertilized with stable manure.
Plot 3 was fertilized with plaster.
Plot 4 was fertilized with wood ashes.

52 FRUIT AND POTATO DISEASES

The seed used was very scabby. Two rows of each plot were
planted with the seed untreated ; the other two rows, with seed
soaked in solution of corrosive sublimate, as above described.

When dug, the potatoes showed the following result : The
figures indicate the per cent, of scabby ones.

Commercial

Stable

fertilizer.

manure.

Pla.ster.

Ashes.

Treated

8 per cent.

3 par cent.

12 per cent.

10 per cent.

Untreated .

37 "

14 "

56 "

41 "

These results show the beneficial effect of treating the seed,
it do not fully bear out the stateme
the effect of the different fertilizers.

but do not fully bear out the statement made above in regard to

BORDEAUX MIXTURE

The Bordeaux mixture continues to recommend itself as the
best all-round remedy for fungous diseases. It is efficient, it
is cheap, and it is easily prepared when one once gets the
" hang" of it and is willing to take pains. Directions should
be carefully followed by those who are unfamiliar with its
preparation.

The ingredients of the Bordeaux mixture are blue vitriol,
lime, and water. The ingredient which kills the fungus is the
blue vitriol. The purpose of the lime is to prevent the injury
to the foliage which a simple solution of blue vitriol would
cause.

The proportion of the ingredients may be varied considera-
bly. The formula which was recommended in Bulletin 27 of
this Station still seems to us a satisfactory one, namely :

Blue vitriol ...... i lb.

Lime, fresh . . . . . • 70 "

Water 10 gals.

As the quantity most frequently prepared would be a barrel,
the formula may be given as follows :

Blue vitriol ... 5 lbs.

Lime .... 3J^ lbs.

Water .... i bbl. (45 to 50 gals.)

THE BORDEAUX MIXTURE =53

For convenience in weighing, 35^ lbs. of lime may be used.
This makes what we have designated as a i to 10 mixture.
The one described below by Mr. Galloway is a i to S}( mix-
ture. It will not do to throw these ingredients together hap-
hazard and expect a good result. The blue vitriol should be
dissolved separately ; this can be done with cold water, but it
requires considerable time and is best done in the way described
by Mr. Galloway. Wiien wanted for immediate use, it may
be dissolved rapidly in hot water, two quarts of which will
dissolve a pound. A good way is to prepare a stock solution
in quantity beforehand, making it of such strength that a half
gallon or a gallon will contain one pound.

Only fresh lime should be used. Select the firm, uncrum-
bled lumps. Slack it by adding water slowly, just enough to
keep it from burning or becoming dry until tlie lumps are all
broken up, then add water enough to make a thin paste. The
method of mixing the solution of blue vitriol and the lime rec-
ommended by Galloway is the ideal one, and even when it is
not convenient to follow it in detail, the principle involved
should be followed ; that is, to dilute both the blue vitriol and
the lime as much as possible before mixing.

If the quantity oi fresh lime given in the formula be used, it
will not be necessary to test the mixture. But it is often con-
venient to make up a considerable quantity of lime paste, and
inconvenient to measure it afterwards ; then a test which will
tell when enough lime has been used will be convenient.

Dissolve a lump of yellow prussiate of potash (which may
be obtained at any drug store) as large as a chestnut in a gill
of water, and keep in a bottle; add a few drops of this to a
saucerful of the prepared mixture. If a brown color appears,
add more lime to the mixture, and test again. When sufficient
lime has been used, no brown color will appear on applying
the prussiate solution. Other tests are given below.

The following explicit directions for making the Bordeaux
mixture were written by Mr. B. T. Galloway, of the United
States Department of Agriculture : In a barrel or other suitable
vessel place twenty-five gallons of water. Weigh out six
pounds of copper sulphate, then tie the same in a piece of
coarse gunny sack, and suspend it just beneath the surface of the

54

FRUIT AND POTATO DISEASES

water. By tying the bag to a stick laid across the top of the
barrel, no further attention will be required. In another ves-
sel slack four pounds of lime, using care in order to obtain a
smooth paste, free from grit and small lumps. To accomplish
this, it is best to place the lime in an ordinary water pail and
add only a small quantity of water at first, say a quart or a
quart and a half. When the lime begins to crack and crumble
and the water to disappear, add another quart or more, exer-
cising care that the lime at no time gets too dry. Toward the
last, considerable water will be required, but if added carefully
and slowly, a perfectly smootii paste will be obtained, pro^vided,
of course, the lime is of good quality. When the lime is
slacked, add sufficient water to the paste to bring the whole up
to twenty-five gallons. When the copper sulphate is entirely

Fig. 3. — Making Bordeaux mixture. Pouring together the lime milk and

copper sulphate solution.

•dissolved and the lime is cool, pour the lime milk and copper
sulphate solution slowly together into a barrel holding fifty gal-
lons, as shown in Fig. 3. The milk of lime should be thoroughly
stirred before pouring. The method described ensures good
mixing, but to complete this work the barrel of liquid should
receive a final stirring, for at least three minutes, with a broad
■wooden paddle.

"It is now necessary to determine whether the mixture is
perfect — that is, if it will be safe to apply it to tender foliage.
To accomplish this, two simple tests may be used. First
insert the blade of a penknife in the mixture, allowing it to

THE BORDEAUX MIXTURE'

55

remain there for at least one minute. If metallic copper forms
on the blade, or, in other words, if the polished surface of the
steel assumes the color of copper plate, the mixture is unsafe
and more lime must be added. If, on the other hand, the blade
of the knife remains unchanged, it is safe to conclude that the
mixture is as perfect as it can be made. As an additional test,
however, some of the mixture may be poured into an old plate
or saucer, and while held between the eyes and the light, the
breath should be gently blown upon the liquid for at least' half
a minute. If tiie mixture is properly made, a thin pellicle,
looking like oil on water, will begin to form on the surface
of the liquid. If no pellicle forms, more milk of lime should
be added."

Fig. 4. — Testing the Bordeaux mixture by tlie plate method.

The Bordeaux mixture should be applied with a pump
designed especially for spraying. Such pumps may be obtained
of almost any hardware dealer. In spraying, it is necessary to
keep the mixture thoroughly stirred. Only freshly made mix-
ture should be used.

Bordeaux Mixture in a Dry Form. — This, in the form
known as " Fungroid," has not proved satisfactory with us.
The potato vines, to which it was applied, showed little, if
any, benefit from its use. It is doubtful if any fungicide in a
powdered form will be as efficient as a liquid one.

HOW TO SPRAY

In Bulletin loi of the Cornell Experiment Station, Prof. L.
H. Bailey, among many other things worth quoting, says, in

56 FRUIT AND POTATO DISEASES

regard to spraying : " Spray thorouglily or not at all. I should
say that fully half the spraying which I have seen in western
New York in the last two or three years is a waste of time and
material. Squirting a few quarts of water at a tree as you
hurry past it, is not spraying A tree is thoroughly and honestly
sprayed when it is tvet all over^ on all tlie branches and on
both sides of all the leaves. An insect or fungus is not killed
until the poison is placed where the pest is." Again he says :
" The farmer should know what he wants to kill, before he
begins to spray. It is common to find a man who is going at
spraying with enthusiasm, but who cannot explain a single
definite object which he has in view. He simply knows upon
general principles that spraying is useful. To such a man,
spraying is spraying, whether he uses Paris green or Bordeaux,
or both, or neither one ; and his results are about equal to his
knowledge. There is no longer excuse for such ignorance,
for all the leading insects and fungi have received more or less
exact treatment in the publications of the experiment stations."

WHEN TO SPRAY WITH BORDEAUX MIXTURE

I^or Scab aiid Other Fungous Diseases of the Apple and
Pear. — Spray once before the blossoms open, and again as soon
as the blossoms fall, and a third time two weeks later.

For Black K?iot on Plum. — Spray once before the buds
begin to swell, and again just before they burst. These spray-
ings are directed against the winter spores. For the summer
spores, spray the last of May and again about the middle of
June.

For Early Blight on Early Potatoes. — Spray when the
vines are about two thirds grown, and a second time two weeks
later.

For Both Early and Late Blight on Late Potatoes. —
Spray three times: the middle of July, the first of August, and
the middle of August.

Rainy weather may render it advisable to spray at shorter
intervals, and to increase the number of sprayings.

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