Plant pathological investigation in the United States V : research in plant pathology and botany at Louisiana State University

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THE PLANT DISEASE REPORTER

Issued By |

THE PLANT DISEASE SURVEY

Division of Mycology and Disease Survey

BUREAU OF PLANT INDUSTRY, SOILS, AND AGRICULTURAL ENGINEERING
AGRICULTURAL RESEARCH ADMINISTRATION

UNITED STATES DEPARTMENT OF AGRICULTURE
SUPPLEMENT 206

PLANT PATHOLOGICAL INVESTIGATION
IN THE UNITED STATES
VW

Supplement 206 September 15, 1951

The Plant Disease Reporter is issued as * service to plant pathologists
throughout the United States. It contains reports, summaries, observations, and
comments submitted voluntarily by qualified observers. These reports often are
in the form of suggestions, queries, and opinions, frequently purely tentative,
offered for consideration or discussion rather than as matters of established
fact. In accepting and publishing this material the Division of Mycology and
Disease Survey serves merely as an informational clearing house. It does not
assume responsibility for the subject matter.

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Issued by

THE PLANT DISEASE SURVEY
DIVISION OF MYCOLOGY AND DISEASE SURVEY

Plant Industry Station Beltsville, Maryland

+ PLANT PATHOLOGICAL INVESTIGATION IN THE UNITED STATES, V

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Plant Disease Reporter |
Supplement 206 September 15, 1951

RESEARCH IN PLANT PATHOLOGY AND BOTANY
aa AT LOUISIANA STATE UNIVERSITY

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Cow: Edgerton

The research work in botany and plant pathology in Louisiana State University and Louisiana
Agricultural Experiment Station practically had its beginning when Adams Fund money became
available in 1906. Previous to that date, W. R. Dodson, who later became director of the Experi-
ment Station, made a study of the sugarcane plant and also reported on the weeds occurring in
rice fields. Although at that time farmers and planters had become somewhat cognizant of such
troubles as the black rot of sweetpotatoes, the cucumber mildew, and some trouble with sugar-
cane, practically no definite information was available in regard to the plant diseases of the State.
Sugarcane planters were perhaps the first to ask for such information.

In 1906, H. R. Fulton was appointed as the first plant pathologist of the Station. During the
two years that he held that position, he made some preliminary studies and surveys, and reported
in bulletins on certain of the diseases of rice, peppers, and beans, and on the root rot of sugar-
cane.

In 1908, following the resignation of Dr. Fulton, C. W. Edgerton was appointed plant
pathologist. As pathologist of the Station and later (1924-1950) as Head of the Department of
Botany, Bacteriology and Plant Pathology in the University, he was in charge of the research
in botany and plant pathology until his retirement in 1950. Upon his retirement, S. J. P. Chiiton
became Chairman of the department and is now in charge of the research work.

Starting from scratch, as would be expected, the additions to the department Staff were at
first very few. C. C. Moreland was appointed as assistant in 1911 and remained on the Staff
with the exception of a few years in the armed services until his resignation in 1924. The depart-
ment began to expand in 1924 and this expansion has continued until the present time. Since
1924, the following have been added to the Staff in the Experiment Station: E. C. Tims (1924-
date); I. L. Forbes (1925-date); E. V. Abbott (1925-26); P. J. Mills (1926-date); A. G. Plakidas
(1927-date); H. H. Flor (1928-30); L. H. Person (1929-47); T. C. Ryker (1936-50); S. J. P.
Chilton (1940-date); P. H. Dunckelman (1940-date); R. T. Gibbens (1940-41); W. J. Luke (1941-
42); F. J. LeBeau (1944-46); J. G. Atkins (1947-date); W. J. Martin (1947-date); E. R. Stamper
(1948-date).

The following men from the teaching faculty have carried on projects of their own or have
assisted in various ways in the research program: C. F. Moreland, W. N. Christopher, C. A.
Brown, L. H. Flint, C. S. McCleskey, L. S. Olive, Mel T. Cook, H. E. Wheeler, H. W.
Johnson, and R. E. Atkinson.

The following research men from the U. S. Department of Agriculture have at times been
stationed in Louisiana with offices in Louisiana State University: D. C. Neal, E. L. LeClerg,

T. P. Dykstra, D. C. Bain and T. T. Ayers at Baton Rouge, and W. H. Tisdale at Crowley.

Much credit should also be extended to the numerous graduate students who have from time
to time carried on projects of their own or have assisted in the Experiment Station investigations.

Louisiana Conditions and Problems

Conditions in Louisiana are extremely favorable for the development and spread of most
plant diseases. The rainfall is heavy (close to 60 inches in the sugarcane belt), the humidity is
relatively high, and the temperatures are usually favorable during most of the year. The winters

‘we Oe

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are comparatively mild and plant growth is seldom at a standstill during any period of the year.
The number of plants grown is very large, including not only those that are adapted to sub-tropical
conditions, but also most short-season crops common to northern climates which find conditions
favorable for growth during the winter months. The plant pathologist finds no stopping place in
his work, nor any season during which he must confine his investigations to the laboratory or the
greenhouse.

During the period covered by this report, which comprises practically the first half of the
20th century, many diseases and disease problems have been under investigation. The major
crops such as sugarcane, cotton, rice, vegetable crops, and strawberries have of necessity
received the most attention, but the diseases of other crops have been studied as time has
allowed. It has also been possible to investigate certain mycological and physiological problems.
During recent years, it has been necessary to take over and push weed control problems.

Sugarcane Diseases

Sugarcane diseases have received a great deal of attention through all the years. Three
diseases of major importance, red rot (Physalospora tucumanensis), root rot, and mosaic have
occurred in the State, along with several others of lesser importance. These diseases have
caused and are still causing heavy losses. There have been periods of declining yields and crop
failures. The prosperity of the sugar industry depends to a very large extent or the efficiency of
the measures that are used to control these diseases. The fact that the 1950 crop was one of
the best on record shows that the methods adopted have been fairly efficient.

The red rot was first observed in the State in 1908. In the years that followed, information
was obtained on the losses caused by the disease, how the fungus enters the plant, how the spores
migrate through the ducts of the fibro-vascular bundles, how the cells of resistant and susceptible
plants react to the invading mycelium, and on the occurrence of the perfect stage. The disease
reduces the sucrose content of the juice and is also often responsible for poor stands in the field.
The mosaic (virus) was recognized in 1919. This disease made it necessary to discard all the
varieties that were being grown at that time. At present, with one exception, all varieties grown
are resistant. Consequently, the disease has lost much of its importance. The root rot, which
is considered to be caused by a complex of factors, is still not very well understood.

The breeding program which has been carried on by the U. S. Department of Agriculture and
now also by the Department of Plant Pathology in the Experiment Station has been responsible for
the production of canes which are fairly resistant to the major diseases. At present, varieties
are not released for planting unless they are resistant.

It is not necessary at this time to present further details in regard to the sugarcane investiga- —
tions. A bulletin has just been published by the Experiment Station concerning work of the depart-
ment on sugarcane diseases (Edgerton, C. W. Forty-two years of sugarcane disease research
at the Louisiana Agricultural Experiment Station. Louisiana Agr. Exp. Sta. Bul. 448. 1950).

A copy of this bulletin may be obtained from the Director of the Experiment Station, L. S. U.,
Baton Rouge, Louisiana.

Cotton Diseases

In the earlier period of the work, considerable attention was given to the diseases of cotton
affecting the bolls. In 1912, a bulletin on the boll rots of cotton was published. This bulletin,
which included the information obtained in Louisiana, has been used as a reference in most cotton-
producing countries of the world. In this bulletin, the Diplodia boll rot was for the first time
listed among the more important cotton diseases. The perfect stage of the cotton anthracnose
(Glomerella gossypii) was reported and data indicating that both the cotton anthracnose and the
angular leaf spot organisms (Xanthomonas malvacearum) could gain entrance to the cotton bolls
through the deteriorating flower parts was presented. It was also shown that the angular leaf spot
lesions on the cotton bolls acted as courts of infection for the anthracnose. It was shown that
the cotton anthracnose was carried over from one season to the next by spores on the surface of
the seed and by mycelium within the seed. It was also shown that these spores and mycelium
would die out during the first year of seed storage. By a longer period of storage, anthracnose-
free seed could be obtained.

In later years, Neal carried on seed treatment tests in Louisiana. In the years when most
of the seed used for planting was treated, there was very little loss in the State from anthracnose
and angular leaf spot. Neal also continued work on the cotton wilt (Fusarium oxysporum f.
vasinfectum) and in the last few years has been observing and studying a small outbreak of Texas

199

root rot (Phymatotrichum omnivorum) in the northwest corner of the State.
Diseases of Vegetable Crops

Many vegetables are grown in Louisiana both for local consumption and for shipment to

| ‘northern markets. From a pathological standpoint, the ones that have received the most attention
‘include: bean, tomato, sweetpotato, Irish potato, eggplant, onion and cucumber.

| Bean Diseases. In the first decade of the 20th century, most of the bean seed used for plant-
‘ing came from Michigan and other northeastern States. A considerable portion of this seed was
‘affected to a greater or less extent with anthracnose (Colletotrichum lindemuthianum). As condi-
‘tions in the spring in Louisiana are very favorable for anthracnose, epidemics were common

‘and severe. In studying the disease, it was found that the causal fungus was definitely a low-
‘temperature organism, having an optimum temperature for growth of 22-239 C. and a maximum
‘around 30° C. This meant that clean seed could be obtained from fields planted in August. Later,
it was found that the disease did not develop in many regions in the West. In recent years, the
‘growers have depended almost entirely on western-grown seed and the disease has practically
disappeared from Louisiana fields.

| The bacterial blights (Xanthomonas phaseoli, Pseudomonas phaseolicola) have also been
|\serious and at the present time are the most serious diseases of the bean. While working on
these troubles, Person found that it was possible to obtain blight-free seed from certain of the
dry valleys in California. For a number of years Louisiana growers contracted for such seed.

‘It is believed that it is possible for seedsmen to obtain bean seed free of the blights as well as

of the anthracnose.

Tomato Diseases. The investigations on tomato diseases in Louisiana began about 1909. At
that time, in many parts of the State, it was impossible to grow the commercial varieties then
available because of tomato wilt. Wilt-resistant varieties of certain other crops, particularly
cotton, had been obtained, and it was reasonable to expect that wilt-resistant varieties of
tomatoes could also be procured. Many varieties were tested in the field and finally a single
plant was found that was highly resistant. This plant had certain undesirable characteristics and
sO was crossed with the Earliana, a variety that was being extensively grown at the time.
‘Eventually two resistant varieties were obtained and were grown on a wide scale in several of the
|southwestern States for a number of years and are still being grown to some extent. These
‘varieties have also been used by geneticists in various parts of the country for breeding purposes.
In the breeding work in Louisiana, a new method of selecting for resistance was developed.
|Seeds were planted in sterilized soil re-infested with the wilt fungus. As susceptible plants

| were either killed or showed the presence of the disease, these were easily eliminated and only
'|plants showing resistance were taken to the field. This method permitted the testing of large
‘numbers of plants.

In the studies on tomato wilt, it was found that the optimum temperature for the growth of
the fungus (Fusarium oxysporum f. lycopersici) in culture and for infection in the field was
‘about 299 C. This explains why the tomato wilt is more severe in the Southern States where the
‘temperatures are relatively high in the spring season.
| The early blight, Alternaria solani, has also been a very important factor in Louisiana. In
early spraying tests, it was found that while the disease could be controlled to a certain extent,
the harvest period was also delayed.

Sweetpotato Diseases. The sweetpotato is one of the major crop plants in Louisiana. During
the first 20 years of the present century, because of declining returns from sugarcane and cotton,
farmers centered around Sunset and Opelousas attempted to substitute the sweetpotato and to
develop a commercial sweetpotato industry. The attempt was outstandingly successful. The
‘industry gradually enlarged, and finally that area became the leading sweetpotato center in the
United States. It must be admitted that the early growers were very fortunate. The industry in
its beginning developed without trouble from any serious disease. The growers used their own
sweetpotatoes for planting purposes and the use of vine cuttings was a common practice. This
method of propagation held the black rot in check and the other serious diseases were not
| introduced.

During World War II and the years immediately preceding, conditions changed. Owing to
increased demands for sweetpotatoes and also a greater demand for early crops, the growers
| shifted to the use of draws for planting. They also shipped draws and seed potatoes in from other
jareas. The production of draws for sale developed into an industry of considerable size. ihe
4 State Department of Agriculture attempted to protect the purchasers of roots and draws by
| requiring that these materials be certified. This requirement was of considerable help, but in

196 |

spite of it the major diseases of sweetpotatoes became established in all of the commercial areas.

There are at present three major diseases of sweetpotatoes in Louisiana, black rot; Sox
rot, and stem rot (Endoconidiophora fimbriata, Actinomyces ipomoea, Fusarium oxysporum f.
batatas). The research work in the Experiment Station has largely been concerned with the first
two.

The losses from black rot increased enormously during this recent period in which the
industry was expanding. As the losses previous to that had been of more or less minor
importance, the growers did not take the necessary precautionary measures to hold it under
control. It soon became a serious trouble, not only in the field and in storage, but also on roots
being shipped to market. Sweetpotatoes are usually washed before shipment. It was found that
roots washed in water badly contaminated with spores of the black rot fungus would be seriously
affected and sometimes become a total loss before reaching the northern markets. In tests made
at the shipping centers, Martin and Person showed that this loss could be largely eliminated by
dipping the roots in a weak borax solution. In recent work, results obtained by U. S. Department
of Agriculture workers at Beltsville have been confirmed. It has been found that exposing black-
rot-affected roots at a temperature of 43° C. for a period of 24 hours destroys the fungus without
injuring the roots. Additional work here indicates that exposures of 30 hours at 40° C. also are
lethal to the fungus in affected roots. This has not as yet been used commercially but the
method looks promising.

The soil rot was first recognized in the vicinity of Sunset in 1934. During the years that
followed, it spread rather rapidly and became a disease of considerable importance. Sweetpotato
growing was abandoned on some farms. Serious trouble has developed only in dry years.

In Louisiana, as had been suggested earlier in other States, it was found that the disease was
caused by an Actinomycete. The organism was isolated and tested and finally in 1940 was
described as a new species, Actinomyces ipomoea, by Person and Martin.

After extensive tests, Person found that the disease could be controlled in the Sunset region
by treating the fields with about 500 lbs. of sulfur per acre. The organism does not live ina soil
testing pH 5.2 or lower. The soils around Sunset ordinarily test about pH 4.8, which could be
reduced to about pH 5.0 by the addition of sulfur, It was found that potatoes could be grown on
such treated soils for several years without additional treatment.

White Potato Diseases. In Louisiana, the Irish potato is grown largely for shipment to
northern markets in the early spring. The yields are not large but prices in the spring are
usually high enough to make the growing of potatces reasonably profitable. The greatest hazards
to the industry have been the occurrence of certain diseases, the most troublesome including the
mosaics, ring rot, and late blight, for which climatic conditions in Louisiana are extremely
favorable for development in epidemic form. Since these diseases are all seed-borne, and
Louisiana growers depend almost entirely upon northern-grown potatoes for planting purposes,
control depends to a great extent upon the measures taken by growers in the northern seed-
producing States.

Between 1910 and 1920, yield in Louisiana dropped to a point too low for potato growing to be
profitable. The cause of the decline was at first not known, but in later years was recognized to
be the extremely high infection with certain mosaics, particularly those of the rugose type.
Mosaics were just becoming recognized then and even potato pathologists did not appreciate their
importance. Also, at that time seed certification programs were just beginning to be set up ina
number of the northern States, first aimed mainly at guaranteeing purity as to variety of the
seed stocks sold for planting.

In Louisiana, the idea developed that it might be possible to obtain certified seed potatoes
from fields showing a minimum of mosaic, or seed stocks from regions in which the mosaic did
not spread rapidly. At first, it was not possible to persuade seed certifying agencies to include
a tolerance for mosaic of less than 30 to 40 percent, but it did not take long to demonstrate that
this high tolerance was entirely unsatisfactory. On the advice of the Experiment Station, a large
shipment of several cars of seed potatoes, said to have been obtained from a field showing about
30 percent of mosaic, was purchased and used for planting in Louisiana in 1921. The growers
barely did better than to get their seed back. Some fields were not harvested. This very suddenly |)
and very definitely settled the question in the negative as to whether seed potatoes with an \
appreciable amount of mosaic could be used for planting in Louisiana. Eventually the tolerance
for mosaic dropped to around 2 percent. With better and more healthy seed stocks, the acreage
planted to potatoes in Louisiana again increased.

The introduction of the ring rot (Corynebacterium sepedonicum) into the United States
presented some problems which were temporarily disturbing. Recognizing the seriousness of the
disease, the Louisiana State Department of Agriculture, on the recommendation of the pathologist
of the Experiment Station, placed a zero tolerance on ring rot on certified potatoes shipped into

197

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the State. This worked out very satisfactorily and the losses from ring rot have been relatively
small.

During the past six or eight years, epidemics of late blight, some of them very destructive,
-have occurred in the State. These epidemics had not been expected, as it had been assumed that
the late blight fungus (Phytophthora infestans) was a low-temperature organism and would not

develop under normal Louisiana conditions. In studying the disease, Martin has isolated strains
that show marked differences in their ability to survive exposures at 36° C. Whether the disease
will continue to be an important factor in the production of potatoes in Louisiana is still not clear.
Onion Diseases. Of the various diseases which attack onions and shallots in Louisiana, the
downy mildew and pink root (Peronospora destructor, Pyrenochaeta terrestris) seem to be the most
important. Thesediseases have from time to time been responsible for declining yields and alsocrop
‘failures. In the years between 1918 and 1921, a survey was made to determine what diseases
/were present and attempts were also made to control the mildew with sprays. Bordeaux mixture
| and Bordeaux with a sticker were used. The waxy surface of the leaves prevents proper cover-
ing with the sprays and the results obtained were not considered satisfactory.
In recent years, Tims has tested many fungicides and stickers with varying results. Tims

}

has also reported on white rot (Sclerotium cepivorum) and several virus diseases which have become
established inthe State. Heis now testing a large number of hybrids hoping that he can find one of good
' quality and also resistant to mildew.

Cucumber Diseases. The growing of cucumbers is.an important industry in certain small
areas of the State. Success in growing this crop, however, has always depended upon how well
the growers have been able to control the two important diseases, downy mildew and anthracnose.
| Downy mildew (Pseudoperonospora cubensis) develops practically every year while anthracnose
(Colletotrichum lagenarium) seems to be important only in wet years.

Bordeaux mixture has been used intermittently for many years to control the mildew. It was
apparently first used shortly after information in regard to it was brought back from Europe by
some of the U. S. Department of Agriculture investigators in the last decade cof the 19th century.
Experiments by the Louisiana Experiment Station on the control of the two diseases have been in
progress for 10 years or more under the direction of Plakidas, LeBeau, and Atkins. It has been
found that Bordeaux mixture will control downy mildew but that considerable injury from burning
is often associated with its use. Bordeaux mixture, however, does not control anthracnose, and
there have been disappointments in the past in years when the conditions were favorable for the
development of this disease. In recent years, the newer fungicides have been tried and it has
been found that certain of them, particularly Fermate and Dithane Z-78, will control both the

mildew and the anthracnose.

—

Cereal Diseases

Investigations have been carried on with the diseases of two of the important cereals grown in
Louisiana, rice and oats. Rice is one of the crops of major importance, being grown mainly in
Southwest Louisiana, and along the Mississippi River and some of the bayous in the southern part
of the State. Oats are grown to a limited extent in various parts of the State, both for winter
grazing and for the production of grain.

Rice Diseases. A report on the rice diseases of Louisiana was made by Fulton as early as
1908. He found four diseases in the State: blast (Piricularia oryzae), green smut (Ustilaginoidea
virens), black smut (Tilletia [Neovossia ] horrida), and a specking of the grains primarily caused
by an insect.

Other diseases have since been recognized in the State. The Cercospora leaf spot, which has
been one of the more important, was studied by Ryker and Chilton, who were able to select
varieties that were temporarily resistant. They found, however, that there were many strains of
Cercospora oryzae differing in pathogenicity. Varieties selected for resistance eventually
became attacked by strains which seemed to be new. About six or eight different strains of the

fungus were isolated and tested.
Other diseases being studied at the present time include Sclerotium stem rot and white tip

(Leptosphaeria calvinii).

Because of recommendations made by the Experiment Station, many growers are now treating
their seed before planting. When conditions for growth have not been satisfactory, better stands
have been obtained with treated seed.

Oat Diseases. Brief mention may be made of two of the more important oat diseases, crown
rust and Helminthosporium blight. Climatic conditions in Louisiana are extremely favorable for
the development and spread of crown rust (Puccinia coronata). For years, the growers were
compelled to depend entirely on varieties of the Texas Red Rustproof group ofoats. As a result

198

of the oat-breeding program, newer varieties eventually became available. These were checked
closely, not only for resistance to rust, but for other desirable characters. The Victoria and _

Bond hybrids were found to be especially valuable. These were accepted by the growers and for a
period of years were the leading varieties in the State.

In a study made of crown rust, Forbes found that the urediniospores do not live over the
summer season in Louisiana. This meant that the spores responsible for the initial infections of
crown rust in December and January must come from outside the State.

The Helminthosporium blight (H. victoriae) was responsible for a change in the oat program.
The disease did not enter the State for two or three years after it had caused trouble in other
regions. Because of the very favorable conditions in Louisiana, it seemed probable that the
disease would be very troublesome. Consequently when the disease was first reported in the
State, a letter was sent to all county agents and to the principal oat growers, recommending that
no further plantings of the Victoria hybrids be made. Fortunately, this recommendation was
very generally followed and the losses from this disease were held to a minimum. Later, studies
of the disease were made by Stamper and Atkins and it was shown that there is little chance of
growing the present Victoria hybrids in southern and central Louisiana.

Forage Crop Diseases

A survey was made of the sorghum plantings in the State by Bain in order to determine what
diseases might be causing serious losses. At the time the survey was made there was a possibility
that the crop might be used for the production of sugar as well as for forage. A new disease,
apparently recently introduced, was found. The cause was a fungus described as Gloeocercospora
sorghi by Bain and Edgerton. The disease has since been found in a number of States, not only
on sorghum but also on corn and a few other grasses.

Fruit Diseases

Of the severalfruits that are grownin Louisianathe strawberry is most important. Others of
lesser importance include figs, pears, peaches, and species of Rubus and Citrus.

Strawberry Diseases. The strawberry is grown very extensively in the southwest part of
the State, being the principal crop in Tangipahoa and parts of Ascension and Livingston Parishes.
The industry was built on the Klondyke variety, which originated in Louisiana many years ago.
For a long period there was little trouble, but eventually, as the industry expanded, Klondyke
became severely attacked by leaf spot and to a lesser extent by the leaf scorch and strawberry-
growing declined. To determine the possibility of control of these diseases, extensive tests
were made by Plakidas in various parts of the strawberry belt and found that almost complete
control could be obtained by spraying with Bordeaux mixture. As a result of these tests, spraying
is practiced very generally by most growers and has very definitely kept the industry ina
prosperous condition. The Bordeaux mixture apparently acts as an eradicant fungicide, the fungus
fruiting structures being killed before the spores are produced. Plakidas has also made an |
extensive study of the fungi causing leaf spot and leaf scorch (Mycosphaerella fragariae, Diplo-
carpon earliana), determining how these fungi enter the strawberry leaf and cause infection.

Plakidas also made some investigation on the strawberry dwarf, a disease now known to be
caused by nematodes (Aphelenchoides). As the disease seems to be of little economic importance,
it has received but little attention in recent years. A new leaf spot which appeared rather
suddenly was also studied. This was called the purple leaf spot and the organism causing it was
described by Plakidas as a new species, Mycosphaerella louisianae.

In recent years strawberry varieties have changed and new pathological problems are develop-
ing which eventually will have to be considered if the industry is to be maintained at a high level.

Fig Diseases. Figs are grown in Louisiana mostly for home use and for sale locally. As the
fruits are attacked very quickly by rot organisms after picking, they are rarely shipped to distant
markets. As early as 1911, Edgerton reported on the diseases of figs then known to occur in the
State, including several diseases caused by well-known organisms, such as anthracnose
(Glomerella cingulata), soft rot (Rhizopus nigricans), rust (Physopella fici), leaf spot ee |
fici), and nematode root galls. Besides these, canker and limb blight were listed as new.
Canker, which develops around the old fruit scars, is caused by a fungus described as Tubercular-
ia fici. The limb blight occurs on the limbs and branches and covers them with the conspicuous |
salmon-colored fructifications. The fungus which causes the disease is now known to be Corticium
salmonicolor, although at the time it was incorrectly identified. This was one of the first reports |
of this tropical fungus on living trees in the United States.

199

In later years other fig diseases appeared, some of them apparently coming in from regions
farther to the south, possibly from the tropics.

An interesting twig blight caused by the fungus Stilbum cinnabarinum (perfect stage,
Megalonectria pseudotrichia) appeared on figs about 1932 and was studied by Tims. The disease
caused death of the twigs, which were covered with the bright red fruiting structures. It spread
rapidly and soon was widespread in all parts of south Louisiana. For some reason which has not
been satisfactorily explained, the disease, after reaching its peak, gradually became less common
-and in a few years almost disappeared.

Leaf blights caused by Rhizoctonia-like fungi have been the most troublesome during the past
30 years. As shown by Tims, the organisms involved include the thread-blight fungus,
Pellicularia koleroga, andoneor more strains of Pellicularia filamentosa. Very commonly large
branches are involved and sometimes the trees are killed. The thread-blight fungus maintains
itself by rhizomorphs on the bark and so is difficult to control. Some control has been obtained
‘} by spraying with eradicant and protectant fungicides.
| Two new leaf spots have been reported in south Louisiana in recent years. The organisms
| Causing them were described by Tims and Olive with the following names, Cephalosporium fici
and Ormathodium fici. oases
| Pear Diseases. The pear blight (Erwinia amylovora) limits very definitely the pear varie-
_ties that can be grown in Louisiana. The varieties grown are mainly members of the resistant
Chinese Sand pear group, the pineapple variety being the one usually planted. For years, this
| variety seemed to be free of any serious disease. About eightor ten years ago, however, the
pear leaf-blight fungus, Fabraea maculata, entered the State, first appearing in the eastern part
' and gradually spreading westward. The Pineapple pear is extremely susceptible to this fungus
and it is not uncommon to see trees practically defoliated. Plakidas found that the fungus over-
winters in the dead leaves on the ground and attacks the new leaves near the ground very early in
the spring. The disease can be controlled by spraying with copper fungicides or with Fermate,
| but very few growers follow the recommendations.
| The Pineapple pear is also very susceptible to the root rot caused by Clitocybe tabescens.

_ Many trees have been killed by this fungus. Plakidas was able to reproduce the disease by inocu-
lating with pure cultures.

Rubus Diseases. Very few attempts have been made in Louisiana to grow species of Rubus
‘| Ona commercial scale. Wild species of blackberries and dewberries grow in such profusion and
the production of fruit is so great that there is little need of commercial plantings. A number of
| diseases attack Rubus plants in Louisiana and some of these undoubtedly would be important if
blackberries or dewberries were to be grown on a commercial scale. One of these, rosette, has
been investigated by Plakidas. In some other sections of the country, this disease is known as
double blossom. It is characterized by the presence of numerous short branches giving a rosette
{| appearance. The flowers are enlarged and severely distorted and fruit formation is prevented.
| It was found that the causal fungus had not been properly classified and it was renamed Cercospor-
ella rubi. The disease is very interesting because of the peculiar host-parasite relationships.
The mycelium does not enter the host cells but remains between the bud scales and the different
flower parts, in close association with the embryonic bud elements. Infection takes place in the
early spring on the young primocanes. Control was obtained by cutting back the young primocanes
_ and by spraying with Bordeaux mixture.

Citrus Diseases. While the citrus industry in Louisiana has never been large, it has been
very important in certain areas, especially along the Mississippi River below New Orleans.
The Department of Plant Pathology of the Experiment Station cooperated closely with the United
States Department of Agriculture and the State Department of Agriculture in the citrus canker
eradication program, during which, with the exception of a small area from slightly above Buras
to the mouth of the River, most of the citrus plantings in the State were destroyed. At present
the disease seems to be totally eradicated. During the past year, another very serious disease
has appeared in the main citrus-growing area of the State, and already has been responsible for
the death of hundreds of trees grafted on sour orange stock. It seems to be identical with or at
least very similar to the quick decline of California and the tristeza of Brazil. The disease has
been reproduced by grafting.

Diseases of Ornamentals

During the past few years, interest in the growing of ornamentals in Louisiana, as well as in
other parts of the South, has increased greatly. As aresult, growers as well as nurserymen are
recognizing the diseases that are present and are increasingly requesting information in regard to
control measures. During recent years, the Department of Plant Pathology has been trying to

200

anticipate the problems that are apt to become important and has started investigations on some ©
of them. As yet, Easter lilies, Oriental arborvitae, Pittosporum, and Camellias have received
the most attention.

Easter Lily Diseases. The growing of Easter lily bulbs in southern Louisiana for shipment
to northern markets has at times been an important industry and would become very important if
satisfactory control measures could be found for some of the serious diseases. The virus
diseases and the black scale have been the most important. Several virus diseases are present
and some of them are serious enough to prevent the growing of bulbs on a commercial scale.
Attempts have been made to control these troubles by roguing and by certification measures, but
the results have not been satisfactory. Investigations on the black scale have been more encourag
ing. This disease is caused by a fungus which Plakidas has named Colletotrichum lilii. The
scales are affected and the bulbs do not grow satisfactorily. Investigations by Plakidas and
LeBeau have shown that it is possible to destroy the fungus by soaking the bulbs for about 48 hours
in a Puratized solution.

Oriental Arborvitae Disease. For atime, the Oriental arborvitae was among the more
important ornamentals planted. Very commonly, however, this plant was affected witha blight
which killed the branches. In studying the disease, Plakidas found that it was caused by a fungus
which he described as Cercospora thujina. He also found that the disease could be controlled by.
spraying with Bordeaux mixture and other copper fungicides. Because of this disease the arbor-
vitae is being planted less and less.

Pittosporum Leafspot. A leafspot on Pittosporum appeared quite suddenly a few years ago.
Plakidas studied the disease and described the organism causing it as Cercospora pittospori.

Camellia Diseases. At present in Louisiana there is more interest in Camellias thaninother
ornamental plants. As conditions must be just right for Camellias, troubles have developed
from time to time. Plakidas has been studying the die-back, which seems to involve soil condi-
tions as well as attack by certain fungi. He has also been investigating certain scab diseases.
Some of these are caused by species of Sphaceloma (Elsinoé), and the cause of others is perhaps
physiological. The flower blight, caused by a species of Sclerotinia, has also appeared in the
State and at present is causing much concern.

|

Mycological Investigations

From time to time, certain strictly mycological problems have received considerable
attention. The investigations have involved not only parasitic organisms but also many others
which have seemed of particular interest or importance. Many of the fungi, on account of the
short life cycle and the ease with which they can be handled, are excellent for working out certain
basic, biological principles. The mycological investigations have included not only life cycle
studies but also taxonomic, physiologic, and cytologic studies.

As a result of the taxonomic studies, many new organisms have been described and more
information has been obtained in regard to certain groups of fungi. For example, the Louisiana
species of Synchytrium have been studied by M. T. Cook over a period of several years. Much
information is now available in regard to the species of this very interesting genus.

Among the more interesting physiologic and cytologic investigations, the work with antibiotic
organisms and the studies made with Glomerella should be mentioned.

Antibiosis Investigations. During the whole course of the investigations covered by this
report, antagonistic or antibiotic organisms living in the soil have been recognized as very
important in eliminating certain pathogenic organisms and in determining the nature of the soil
flora, and indirectly soil fertility. In one of the early publications on the bean anthracnose, it
was shown that certain soil organisms, particularly a species of Fusarium, were important in
killing out the anthracnose fungus in lesions on the seeds and on the emerging cotyledons.

Later, while the sugarcane root rot was being investigated, Tims isolated an Actinomycete
which he reported in 1932 as being definitely antagonistic to the root-rot Pythium. In 1938,
LeBeau reported that a species of Trichoderma could under some conditions destroy this Pythium.

In recent years, Cooper and Chilton made a survey of the Actinomycetes in the soils of the
Sugar Belt that were antibiotic to the root rot Pythium. From 18 to 31'percent of the Actino-
mycetes isolated were definitely antibiotic to Pythium in culture.

Glomerella investigations. Fungi of the genus Glomerella have been found to be extremely
valuable for physiologic, cytologic and genetic studies. In 1912, Edgerton reported that with
some of these, two strains designated plus and minus commonly occur. It was shown that when
the two strains were placed in a culture plate, a dense ridge of perithecia formed on the line of
contact where they grew together. In 1940 Chilton initiated genetic studies on this organism,
and Lucas, Wheeler, McGahen, Ernest and Olive, have used various Glomerella strains for

201

-) genetic, physiologic and cytologic studies, and a series of papers based on these studies has
been published. At present, the radioactive isotope, Gi is being used by Wheeler in some of

the investigations.

Weed Control Investigations

In recent years, interest in weeds and weed control has increased very rapidly in Louisiana
as well as in other parts of the United States. At the present time many States, including
Louisiana, have active projects on weed control. The present interest may be said to have had
its beginning when it was discovered that certain weeds were very Sensitive to 2, 4-D and could
be killed by extremely small amounts of this chemical when applied in dusts or sprays. In
Louisiana, investigations have been mainly in the Department of Botany and Plant Pathology, but
with the cooperation of the Department of Agricultural Engineering.

Weed control investigations in Louisiana started when the State Legislature in 1944 made an
appropriation to the Experiment Station for the eradication of the alligator weed (Alternanthera
phylloxeroides), which had become a very serious pest in sugarcane fields in South Louisiana.
A project was set up in the Department of Botany and Plant Pathology. At the time it was realized
that it might be very difficult to find satisfactory control measures for this weed. To begin
with, the various herbicides then known were tested. Fortunately, shortly after the work
started, 2,4-D became available and this chemical was immediately included in the tests then
being made by Brown and Ryker. The alligator weed was found to be very sensitive to 2,4-D
and the planters were quick to follow the control recommendations made by the Department. As
a result, in two to three years time, this weed ceased to be a problem in cultivated fields. At
the same time, Ryker also demonstrated that a number of the important weeds in rice fields
could be controlled with 2,4-D.

As the results obtained from the preliminary investigations on weed control were so en-
couraging, it was only natural for the farmers and the planters in the State to insist that the weed
projects be enlarged and that attempts be made to find successful control measures for some of
the other serious weeds of the State. In cooperation with many of the chemical companies
interested in herbicides, extensive investigations have been made on the control of a number of
the important weeds, including Johnson grass and the weeds in cotton fields. Johnson grass is
unquestionably the most troublesome weed in the State, and because it spreads by both rhizomes
and seed, it is a very difficult plant to eradicate. Very promising results have been obtained
by combining summer fallow with pre-emergence and post-emergence sprays. In 1951, many
planters will use every effort to control Johnson grass in their fields. In the extensive tests in
the cotton weed investigations, it has been necessary to use contact herbicides such as the oils
and dinitro compounds, with some very encouraging results. In 1951, tests will be made ona
large scale.

Graduate Instruction

During the past 20 years graduate instruction and graduate work in general in the Department
of Botany and Plant Pathology have expanded rapidly. This expansion has been aided by a grant
from the General Education Board and by the establishment of graduate fellowships by Louisiana
‘State University. With the exception of the war years, there have been from 15 to 25 registered
graduate students each year. In this period, more than 80 Master of Science degrees and 19
Doctor of Philosophy degrees have been granted. The graduate students have mostly worked very
closely with the research men in the Department.

LOUISIANA STATE UNIVERSITY, BATON ROUGE

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