• TABLE OF CONTENTS
HIDE
 Front Cover
 Table of Contents
 Introduction
 Description
 History
 Infection in the seed beds
 The fungus
 Growth of fungus
 Development of apothecia
 Infection experiments
 Other plants affected
 Treatment






Group Title: Bulletin - Florida Agricultural Experiment Station ; 116
Title: Lettuce drop
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
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Permanent Link: http://ufdc.ufl.edu/UF00026711/00001
 Material Information
Title: Lettuce drop
Series Title: Bulletin University of Florida. Agricultural Experiment Station
Physical Description: p. 25-32 : ill. ; 23 cm.
Language: English
Creator: Burger, O. F ( Owen Francis ), 1885-1928
Publisher: University of Florida Agricultural Experiment Station
Place of Publication: Gainesville Fla
Publication Date: 1913
 Subjects
Subject: Lettuce -- Diseases and pests -- Florida   ( lcsh )
Fungal diseases of plants -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by O.F. Burger.
General Note: Cover title.
Funding: This collection includes items related to Florida’s environments, ecosystems, and species. It includes the subcollections of Florida Cooperative Fish and Wildlife Research Unit project documents, the Florida Sea Grant technical series, the Florida Geological Survey series, the Howard T. Odum Center for Wetland technical reports, and other entities devoted to the study and preservation of Florida's natural resources.
 Record Information
Bibliographic ID: UF00026711
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 000921871
oclc - 18160492
notis - AEN2339

Table of Contents
    Front Cover
        Page 25
    Table of Contents
        Page 26
    Introduction
        Page 27
    Description
        Page 27
    History
        Page 27
    Infection in the seed beds
        Page 28
    The fungus
        Page 28
    Growth of fungus
        Page 29
    Development of apothecia
        Page 30
    Infection experiments
        Page 31
    Other plants affected
        Page 32
    Treatment
        Page 32
Full Text
BULLETIN 116


UNIVERSITY OF FLORIDA

Agricultural Experiment Station





LETTUCE DROP

BY

O. F. BURGER


Fig. 1.-Germinated sclerotia of Lettuce Drop fungus, with apothecia.

The Station bulletins will be sent free upon application to the Experiment
Station, Gainesville, Fla.

Pepper Pub. & Ptg. Co.. Gainesville, Fla,


OCTOBER, 1913


1: :

















CONTENTS
PAGE
Introduction ----------------------- ....---------- ----------------- 27
Description --------------------------------- -------------------- 27
History....--------.. -- -------------------------------------------- 27
Infection in the Seed Beds ...------------. ------------ ..--.---- ------ 28
The Fungus --------------------------------------------------------- 28
Growth of Fungus---- -------------.... ..-----.---------- ------------. 29
Development of Apothecia ..-------..---.. -- -------------... ---------- 30
Infection Experiments....----------..---...--------------------------- 31
Other Plants Affected ..-...--.------- .---.. .---.---.---..---------- 32
Treatment --.----.. -------------------------------------------- 32




SUMMARY

1. Lettuce Drop is caused by a fungus known as Sclerotinia libertiana.
2. This disease is tided over from one lettuce season to another by
means of black bodies known as sclerotia.
3. These sclerotia produce spores in Florida during fall, winter, and
spring.
4. These spores must first grow in dead vegetable matter before the
fungus can infect living lettuce plants.
5. The life habits of the fungus are such that we cannot expect to con-
trol the disease by means of spraying the plants.
6. The only practical way of controlling the disease is by a conscientious
removal of every diseased plant from the field as soon as it shows signs of
being infected.
7. It is advisable to treat the place occupied by a diseased plant with
Bordeaux mixture or copper sulphate solution.
8. Foot Rot in celery is caused by the same fungus which causes Drop
in lettuce. Cabbage is also affected by this fungus.












LETTUCE DROP

BY O. F. BURGER



Not many years ago lettuce was regarded as a garden crop,
and used only for home consumption. But to-day lettuce growing
is a large industry. The biennial report of the Commissioner of
Agriculture of Florida for the years 1911 and 1912 gives the num-
ber of acres planted in lettuce as 2,598, which were valued at
$818,307. The fall crop is grown in the open field, but in the
northern part of the State the winter crop is grown under canvas.
There are only a few diseases of lettuce which give the grower
trouble. These are Lettuce Drop, Lettuce Rot, and Root Knot.
In this bulletin only Lettuce Drop will be considered.


DESCRIPTION

Lettuce Drop can be readily distinguished from any other let-
tuce disease. The rotting of the plants first attracts the eye. The
very first sign is the wilting of one leaf. Sometimes only one side
of the plant becomes affected at first. But usually the whole plant
is involved, one leaf after the other sinking until all the lower
leaves have dropped. Later the head becomes affected and falls
over, and the whole plant appears as if scalded with hot water.
On the under side of the lower leaves there is a white cottony fun-
gus. Later there appear nodules which become black. These
black bodies can be found in any of the decayed parts of the
plants, especially in decayed stalks.


HISTORY

Lettuce drop may be caused by more than one fungus.
(There have been three fungi found associated with drop in differ-
ent sections of the United States; Sclerotinia, Pythium, and Bo-












LETTUCE DROP

BY O. F. BURGER



Not many years ago lettuce was regarded as a garden crop,
and used only for home consumption. But to-day lettuce growing
is a large industry. The biennial report of the Commissioner of
Agriculture of Florida for the years 1911 and 1912 gives the num-
ber of acres planted in lettuce as 2,598, which were valued at
$818,307. The fall crop is grown in the open field, but in the
northern part of the State the winter crop is grown under canvas.
There are only a few diseases of lettuce which give the grower
trouble. These are Lettuce Drop, Lettuce Rot, and Root Knot.
In this bulletin only Lettuce Drop will be considered.


DESCRIPTION

Lettuce Drop can be readily distinguished from any other let-
tuce disease. The rotting of the plants first attracts the eye. The
very first sign is the wilting of one leaf. Sometimes only one side
of the plant becomes affected at first. But usually the whole plant
is involved, one leaf after the other sinking until all the lower
leaves have dropped. Later the head becomes affected and falls
over, and the whole plant appears as if scalded with hot water.
On the under side of the lower leaves there is a white cottony fun-
gus. Later there appear nodules which become black. These
black bodies can be found in any of the decayed parts of the
plants, especially in decayed stalks.


HISTORY

Lettuce drop may be caused by more than one fungus.
(There have been three fungi found associated with drop in differ-
ent sections of the United States; Sclerotinia, Pythium, and Bo-












LETTUCE DROP

BY O. F. BURGER



Not many years ago lettuce was regarded as a garden crop,
and used only for home consumption. But to-day lettuce growing
is a large industry. The biennial report of the Commissioner of
Agriculture of Florida for the years 1911 and 1912 gives the num-
ber of acres planted in lettuce as 2,598, which were valued at
$818,307. The fall crop is grown in the open field, but in the
northern part of the State the winter crop is grown under canvas.
There are only a few diseases of lettuce which give the grower
trouble. These are Lettuce Drop, Lettuce Rot, and Root Knot.
In this bulletin only Lettuce Drop will be considered.


DESCRIPTION

Lettuce Drop can be readily distinguished from any other let-
tuce disease. The rotting of the plants first attracts the eye. The
very first sign is the wilting of one leaf. Sometimes only one side
of the plant becomes affected at first. But usually the whole plant
is involved, one leaf after the other sinking until all the lower
leaves have dropped. Later the head becomes affected and falls
over, and the whole plant appears as if scalded with hot water.
On the under side of the lower leaves there is a white cottony fun-
gus. Later there appear nodules which become black. These
black bodies can be found in any of the decayed parts of the
plants, especially in decayed stalks.


HISTORY

Lettuce drop may be caused by more than one fungus.
(There have been three fungi found associated with drop in differ-
ent sections of the United States; Sclerotinia, Pythium, and Bo-






Florida Agricultural Experiment Station


trytis.) The lettuce drop in Florida is caused, however, by
Sclerotinia libertiana.
This disease was first reported from Florida in 1896, from
North Carolina in 1897, and from Massachusetts in 1900. The
disease is now known in all the South Atlantic States (North
Carolina, South Carolina, Alabama, Georgia and Florida), and also
in Louisiana, Massachusetts, New York, Ohio, Pennsylvania, Con-
necticut, Rhode Island, Wisconsin, Iowa, Washington, Vermont,
Maine, Maryland, Delaware, and Virginia. The disease spreads
rapidly and is persistent in affected fields.
Since 1896, damages have been caused by Lettuce Drop in dif-
ferent places in Florida, ranging from 5 per cent. to a total loss
of the crop. The greatest damage noticed by the writer occurred
in a field which had been planted in lettuce for four consecutive
seasons. In this case the grower did not realize enough from his
crop to pay for the fertilizer. In an adjoining field where lettuce
had been planted for three years, the drop was not so severe.
The grower said, however, that every year the drop became worse
on that piece of land.


INFECTION IN THE SEED BEDS

Often many plants die in the seedbeds. Sometimes this occurs
in continuous areas which are called by the grower "bald-headed"
spots. If plants are taken from near one of these spots and set
out in the field they become affected with the drop later in the
season.


THE FUNGUS

It has been demonstrated by other writers, by isolation and
infection that Lettuce Drop is caused by Sclerotinia libertiana.
This fungus shows itself as a white cottony mass on the un-
der side of each infected leaf, in which small bodies are formed, at
first yellowish white and then black (the sclerotia).
The fungus tides itself over unfavorable periods by forming
these sclerotia. They vary from the size of a pin-head to three-
quarters of an inch. When the lettuce plant is in the last stage






Florida Agricultural Experiment Station


trytis.) The lettuce drop in Florida is caused, however, by
Sclerotinia libertiana.
This disease was first reported from Florida in 1896, from
North Carolina in 1897, and from Massachusetts in 1900. The
disease is now known in all the South Atlantic States (North
Carolina, South Carolina, Alabama, Georgia and Florida), and also
in Louisiana, Massachusetts, New York, Ohio, Pennsylvania, Con-
necticut, Rhode Island, Wisconsin, Iowa, Washington, Vermont,
Maine, Maryland, Delaware, and Virginia. The disease spreads
rapidly and is persistent in affected fields.
Since 1896, damages have been caused by Lettuce Drop in dif-
ferent places in Florida, ranging from 5 per cent. to a total loss
of the crop. The greatest damage noticed by the writer occurred
in a field which had been planted in lettuce for four consecutive
seasons. In this case the grower did not realize enough from his
crop to pay for the fertilizer. In an adjoining field where lettuce
had been planted for three years, the drop was not so severe.
The grower said, however, that every year the drop became worse
on that piece of land.


INFECTION IN THE SEED BEDS

Often many plants die in the seedbeds. Sometimes this occurs
in continuous areas which are called by the grower "bald-headed"
spots. If plants are taken from near one of these spots and set
out in the field they become affected with the drop later in the
season.


THE FUNGUS

It has been demonstrated by other writers, by isolation and
infection that Lettuce Drop is caused by Sclerotinia libertiana.
This fungus shows itself as a white cottony mass on the un-
der side of each infected leaf, in which small bodies are formed, at
first yellowish white and then black (the sclerotia).
The fungus tides itself over unfavorable periods by forming
these sclerotia. They vary from the size of a pin-head to three-
quarters of an inch. When the lettuce plant is in the last stage






Bulletin 116


of decay, these black bodies can be picked out of the mass. As
many as 110 sclerotia of different sizes have been picked out of
one diseased lettuce plant.
After the sclerotia have been in the soil for a time they put
out small mushroom-like fruiting bodies, apothecia (Fig. 1).
These are only one-quarter to one-third of an inch in diameter,
and are borne on the top of a stalk (stipe) a quarter of an inch to
one inch long. Within these apothecia there are small sacs (asci)
containing the spores (Fig. 2). When there is enough pressure
within the ascus, the top is pushed off and the spores ejected.
F. L. Stevens (North Carolina Agr. Exp. Station, Bulletin 217),
estimates the number of these spores in one apothecium to be
about 31,000,000, and that a single sclerotium may bear as many
as ten apothecia.


GROWTH OF FUNGUS

The fungus was isolated from diseased ma-
Sterial and transferred cultures made on various
Kinds of media, among them sterilized (green)
S beans, regular agar, and cracked corn. There was
i a good growth of mycelium on the different media.
In fourteen days after inoculation all the tubes had
Developed sclerotia. The hyphae when they came
in contact with the walls of the tube began to
\ branch and formed appressoria, or hold-fasts. The
appressoria were round, black bodies, from an
Fig. 2.-Ascus eighth to a quarter inch in diameter.
with spores. A culture on regular agar plates was made
from an apothecium on February 6. On February
7, the spores began to germinate, and on February 14, sclerotia
were formed on the agar in each plate.
In.December, transfers were made from agar cultures to
cracked corn, and sclerotia were formed in a few days. In Jan-
uary the sclerotia began to germinate. By February the pro-
cesses had dried, and new ones were being put out. The pro-
cesses or stipes were sterile, no disk was formed, and dissection
did not reveal any aborted or young asci. They varied from one-
eighth of an inch to an inch in length.





Florida Agricultural Experiment Station


Fig. 3.-Sclerotia growing on agar
plate. Natural size.


DEVELOPMENT OF APOTHECIA
Sclerotia were gathered at different times during the lettuce
season with a view of finding out what factors controlled the pro-
duction of apothecia. Over four hundred sclerotia were placed
in boxes filled with potting soil and placed in the open. Other
sclerotia were put in test-tubes which contained sterilized potting
soil. Some of the tubes were kept in an ice chest, while the rest
were kept at room temperature.
The sclerotia referred to above were gathered and placed in
the boxes on March 25, 1912. On November 22, 1912, the first
apothecium was found; and on March 20, 1913, the last apo-
thecium was gathered from these boxes. The greatest number
of apothecia, 30, found in one day was on January 1. The apo-
thecia ranged in diameter from an eighth to a quarter of an inch.
On December 18, 1912, about two hundred sclerotia were
gathered from diseased plants in the field and placed in a third
box. On January 25, 1913, these sclerotia produced the first apo-
thecium. On February 20, 1913, about two hundred more sclero-
tia were gathered from diseased plants and placed in another box.
On March 27, apothecia began to appear in this box, and continued
to be produced until April 19, 1913. After that date no apothe-






Bulletin 116


cia were found in any of the boxes. It seems that temperature
and moisture are determining causes for the production of apo-
thecia. The mean monthly temperature for each month from
November to May was below 67 degrees F. The lowest mean
temperature was that of February, with 59.2 degrees F.
During the latter part of November complaints were received
from the lettuce-growing districts that the drop had commenced
in the lettuce fields. This corresponds with the time apothecia
began to appear in the experiment boxes. Complaints of "bald-
headed" spots, occurring in the seed beds, were received also.
This seems to indicate that the production of apothecia in the
boxes was coincident with the production of apothecia in the let-
tuce fields. F. L. Stevens (in Bul. 217, North Carolina Agr. Exp.
Station) says: "The sclerotium germinates under suitable condi-
tions, usually after a lapse of several months to nearly a year
under field conditions." In Florida under favorable field condi-
tions, sclerotia may form apothecia in about thirty days.
The sclerotia used in the following experiment were gath-
ered from diseased lettuce plants on February 15, 1913, and had
been standing in an open dish at room temperature until used.
Sets of six tubes partially filled with sterilized soil were taken at
irregular intervals, and five of the sclerotia were dropped into
each tube. Three tubes of a set were then placed in an ice chest
where the temperature was kept between 52 and 66 degrees F.,
and the other three tubes were placed in the culture closet, which
was kept at room temperature. The different sets were started
on the following dates: March 1, 10, 28, April 12, 29, May 22,
and June 5. Notes were taken, at irregular intervals, on March
28, April 9, June 5, 24, and July 30. In the tubes placed in the
culture closet, and kept at room temperature, no apothecia were
formed, but in some tubes there was a mycelial growth. Sterile
processes only were produced in all the tubes placed in the ice
chest, spore-bearing apothecia were not produced. The above
experiment shows that temperature is an important factor in the
production of apothecia.

INFECTION EXPERIMENTS

Infection experiments were tried by placing bits of mycelium
on plants, and by placing spores in healthy and injured tissue.
On February 12, 1913, small pieces of apothecia were dropped
on healthy lettuce plants. No infection occurred.
On February 20, 1913, pieces of apothecia were placed at the
base of leaves of five plants where an injury had been made with
a sterile scalpel. In 30 days, one plant was entirely decayed, and
three were badly affected, while one plant remained healthy.
On February 20, 1913, pieces of apothecia were placed at the






Florida Agricultural Experiment Station


ground line of five healthy plants. In a month all plants were
infected.
On February 12, sixteen healthy plants were treated, by plac-
ing some mycelium from a pure culture in contact with uninjured
portions of each plant. On February 24, fifteen of the plants
were affected with the drop.


OTHER PLANTS AFFECTED BY SCLEROTINIA
LIBERTIANA

In the celery fields the crop is affected by a disease known
as Root Rot. It has been shown by other writers that this dis-
ease is due to Sclerotinia libertiana, the same fungus that causes
Lettuce Drop. In handling this disease in a celery fieldit would
be well to follow the same treatment as recommended for lettuce.
The writer found about 2 per cent. of a cabbage crop affected
with this disease in a field that had been planted to lettuce the
previous year. The sclerotia were found in the stalks in consid-
erable numbers.

TREATMENT
(1) All diseased plants should be removed from the field as
soon as they are known to be infected.
(2) Drench the place where the infected plant stood with
Bordeaux mixture, 5-5-50 formula, or with bluestone dissolved
in water (one pound to seven gallons of water).
(3) Do not follow a crop of lettuce with celery or celery
with lettuce, as both crops are subject to this disease, Foot Rot in
celery being caused by Sclerotinia libertiana.
(4) Set out only healthy plants. Do not take plants which
are growing near diseased areas in beds ("bald-headed spots").






Florida Agricultural Experiment Station


ground line of five healthy plants. In a month all plants were
infected.
On February 12, sixteen healthy plants were treated, by plac-
ing some mycelium from a pure culture in contact with uninjured
portions of each plant. On February 24, fifteen of the plants
were affected with the drop.


OTHER PLANTS AFFECTED BY SCLEROTINIA
LIBERTIANA

In the celery fields the crop is affected by a disease known
as Root Rot. It has been shown by other writers that this dis-
ease is due to Sclerotinia libertiana, the same fungus that causes
Lettuce Drop. In handling this disease in a celery fieldit would
be well to follow the same treatment as recommended for lettuce.
The writer found about 2 per cent. of a cabbage crop affected
with this disease in a field that had been planted to lettuce the
previous year. The sclerotia were found in the stalks in consid-
erable numbers.

TREATMENT
(1) All diseased plants should be removed from the field as
soon as they are known to be infected.
(2) Drench the place where the infected plant stood with
Bordeaux mixture, 5-5-50 formula, or with bluestone dissolved
in water (one pound to seven gallons of water).
(3) Do not follow a crop of lettuce with celery or celery
with lettuce, as both crops are subject to this disease, Foot Rot in
celery being caused by Sclerotinia libertiana.
(4) Set out only healthy plants. Do not take plants which
are growing near diseased areas in beds ("bald-headed spots").




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