• TABLE OF CONTENTS
HIDE
 Front Cover
 Credits
 Table of Contents
 Introduction
 Losses due to physical factors
 Premature seeding or "bolting"
 Damping-off
 Control of other diseases...
 Discussion














Group Title: Bulletin - University of Florida Agricultural Experiment Station ; 397
Title: Controlling damping-off and other losses in celery seedbeds
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 Material Information
Title: Controlling damping-off and other losses in celery seedbeds
Series Title: Bulletin - University of Florida Agricultural Experiment Station ; 397
Physical Description: Book
Language: English
Creator: Townsend, G. R.
Publisher: University of Florida Agricultural Experiment Station
Publication Date: 1944
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Bibliographic ID: UF00027594
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.

Table of Contents
    Front Cover
        Page 1
    Credits
        Page 2
        Page 3
    Table of Contents
        Page 4
    Introduction
        Page 5
    Losses due to physical factors
        Page 6
        Page 7
        Page 8
        Page 9
    Premature seeding or "bolting"
        Page 10
    Damping-off
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
        Page 23
        Page 24
    Control of other diseases and insects
        Page 25
    Discussion
        Page 26
        Page 27
Full Text


Bulletin 397


UNIVERSITY OF FLORIDA
AGRICULTURAL EXPERIMENT STATION
HAROLD MOWRY, Director
GAINESVILLE, FLORIDA





CONTROLLING DAMPING-OFF

AND OTHER LOSSES IN

CELERY SEEDBEDS

By G. R. TOWNSEND


Fig. 1.-Celery plants are started on irrigated beds under muslin covers.


Single copies free to Florida residents upon request to
AGRICULTURAL EXPERIMENT STATION
GAINESVILLE, FLORIDA


March, 1944










BOARD OF CONTROL

H. P. Adair, Chairman, Jacksonville
N. B. Jordan, Quincy
T. T. Scott, Live Oak
Thos. W. Bryant, Lakeland
M. L. Mershon, Miami
J. T. Diamond, Secretary, Tallahassee

EXECUTIVE STAFF

John J. Tigert, M.A., LL.D., President of the
University3
Harold Mowry, M.S.A., Director
L. O. Gratz, Ph.D., Asst. Dir., Research
W. M. Fifield. M.S., Asst. Dir., Admin.4
J. Francis Cooper, M.S.A., Editor8
Clyde Beale, A.B.J., Assistant Editors
Jefferson Thomas, Assistant Editors
Ida Keeling Cresap, Librarian
Ruby Newhall, Administrative Managers
K. H. Graham, LL.D., Business Managers
Claranelle Alderman, Accountants

MAIN STATION, GAINESVILLE

AGRONOMY

W. E. Stokes, M.S., Agronomist1
Fred H. Hull, Ph.D., Agronomist
G. E. Ritchey, M.S., Agronomist2
W. A. Carver, Ph.D., Associate
Roy E. Blaser, M.S., Associate
G. B. Killinger, Ph.D., Agronomist
H. C. Harris, Ph.D., Associate
R. W. Bledsoe, Ph.D., Assistant
Fred A. Clark, B.S., Assistant

ANIMAL INDUSTRY

A. L. Shealy, D.V.M., An. Industrialist' a
R. B. Becker, Ph.D., Dairy Husbandmans
E. L. Fouts, Ph.D., Dairy Technologists
D. A. Sanders, D.V.M., Veterinarian
M. W. Emmel, D.V.M., Veterinarian3
L. E. Swanson, D.V.M., Parasitologist*
N. R. Mehrhof, M.Agr., Poultry Husb.3
T. R. Freeman, Ph.D., Asso. in Dairy Mfg.
R. S. Glasscock, Ph.D., Asso. An. Hush.
D. J. Smith, B.S.A., Asst. An. Husb.'
P. T. Dix Arnold, M.S.A., Asst. Dairy Husb.3
G. K. Davis, Ph.D., Animal Nutritionist
C. L. Comar, Ph.D., Asso. Biochemist
L. E. Mull, M.S., Asst. in Dairy Tech.'
0. K. Moore, M.S., Asst. Poultry Husb.3
J. E. Pace, B.S., Asst. An. Husbandmans
S. P. Marshall, M.S., Asst. in An. Nutrition
C. B. Reeves, B.S., Asst. Dairy Tech.

ECONOMICS, AGRICULTURAL

C. V. Noble, Ph.D., Agr. Economist' 3
Zach Savage, M.S.A., Associate
A. H. Spurlock, M.S.A., Associate
Max E. Brunk, M.S., Assistant


ECONOMICS, HOME

Ouida D. Abbott, Ph.D., Home Econ.1
Ruth O. Townsend, R.N., Assistant
R. B. French, Ph.D., Biochemist


ENTOMOLOGY

J. R. Watson, A.M., Entomologist1
A. N. Tissot, Ph.D., Associates
H. E. Bratley, M.S.A., Assistant


HORTICULTURE

G. H. Blackmon, M.S.A., Horticulturist'
A. L. Stahl, Ph.D., Asso. Horticulturist
F. S. Jamison, Ph.D., Truck Hort.
R. J. Wilmot, M.S.A., Asst. Hort.
R. D. Dickey, M.S.A., Asst. Hort.4
J. Carlton Cain, B.S.A., Asst Hort.'
Victor F. Nettles, M.S.A., Asst. Hort.'
Byron E. Janes, Ph.D., Asst. Hort.
F. S. Lagasse, Ph.D., Asso. Hort.2
H. M. Sell, Ph.D., Asso. Horticulturists



PLANT PATHOLOGY

W. B. Tisdale, Ph.D., Plant Pathologist1 s
Phares Decker, Ph.D., Asso. Plant Path.
Erdman West, M.S., Mycologist
Lillian E. Arnold, M.S., Asst. Botanist


SOILS

R. V. Allison, Ph.D., Chemist'
Gaylord M. Volk, M.S., Chemist
F. B. Smith, Ph.D., Microbiologists
C. E. Bell, Ph.D., Associate Chemist
L. E. Ensminger, Ph.D., Soils Chemist
J. R. Henderson, M.S.A., Soil Technologist
L. H. Rogers, Ph.D., Associate Biochemist*
R. A. Carrigan, B.S., Asso. Biochemists
G. T. Sims, M.S.A., Associate Chemist
J. N. Howard, B.S., Assistant Chemist
T. C. Erwin, Assistant Chemist
H. W. Winsor, B.S.A., Assistant Chemist
Geo. D. Thornton, M.S., Asst. Microbiologist
R. E. Caldwell, M.S.A., Asst. Soil Surveyor'
Olaf C. Olson, B.S., Asst. Soil Surveyor



1 Head of Department.
2 In cooperation with U. S.
Cooperative, other divisions, U. of F
SIn Military Service.
5 On leave.
















BRANCH STATIONS
NORTH FLORIDA STATION, QUINCY

J. D. Warner, M.S., Vice-Director in Charge
R. R. Kincaid, Ph.D., Plant Pathologist
V. E. Whitehurst, Jr., B.S.A., Asst. An. Hush.4
W. C. McCormick, B.S.A., Asst. An. Hush.
Jesse Reeves, Asst. Agron., Tobacco
W. H. Chapman, M.S., Asst. Agron.'
R. C. Bond, M.S.A., Asst. Agronomist

Mobile Unit, Monticello
R. W. Wallace, B.S., Associate Agronomist

Mobile Unit, Milton
Ralph L. Smith, M.S., Associate Agronomist

CITRUS STATION, LAKE ALFRED

A. F. Camp, Ph.D., Vice-Director in Charge
V. C. Jamison, Ph.D., Soils Chemist
B. R. Fudge, Ph.D., Associate Chemist
W. L. Thompson, B.S., Entomologist
W. W. Lawless, B.S., Asst. Horticulturist*
R. K. Voorhees, Ph.D., Asso. Plant Path.
C. Stearns, Jr., B.S.A., Asso. Chemist
H. 0. Sterling, B.S., Asst. Horticulturist
T. W. Young, Ph.D., Asso. Horticulturist
J. W. Sites, M.S.A., Asso. Horticulturist


EVERGLADES STA., BELLE GLADE

J. R. Neller, Ph.I,, Vice-Director in Charge
J. W. Wilson, Sc.D., Entomologist4
F. D. Stevens, B.S., Sugarcane Agron.
Thomas Bregger, Ph.D., Sugarcane
Physiologist
G. R. Townsend, Ph.D., Plant Pathologist
R. W. Kidder, M.S., Asst. An. Husb.
W. T. Forsee, Jr., Ph.D., Asso. Chemist
B. S. Clayton, B.S.C.E., Drainage Eng.2
F. S. Andrews, Ph.D., Asso. Truck Hort.4
R. A. Bair, Ph.D., Asst. Agronomist
E. C. Minnum, M.S., Asst. Truck Hort.
N. C. Hayslip, B.S.A., Asst. Entomologist


SUB-TROPICAL STA., HOMESTEAD

Geo. D. Ruehle, Ph.D., Vice-Director in
Charge
S. J. Lynch, B.S.A., Asso. Horticulturist
P. J. Westgate, Ph.D., Asso. Horticulturist


W. CENT. FLA. STA., BROOKSVILLE

Clement D. Gordon, Ph.D., Asso. Poultry
Geneticist in Charge2

RANGE CATTLE STA., ONA

W. G. Kirk, Ph.D., Vice-Director in Charge
E. M. Hodges, Ph.D., Asso. Agron., Wauchula
Gilbert A. Tucker, B.S.A., Asst. An. Hush.'


FIELD STATIONS

Leesburg
M. N. Walker, Ph.D., Plant Path. in Charge'
E. M. Andersen, Ph.D., Asso. Hort. in Charge

Plant City
A. N. Brooks, Ph.D., Plant Pathologist

Hastings
A. H. Eddins, Ph.D., Plant Pathologist
E. N. McCubbin, Ph.D., Truck Horticulturist

Monticello
S. 0. Hill, B.S., Asst. Entomologist2 4
A. M. Phillips, B.S., Asst. Entomologist2

Bradenton
J. R. Beckenbach, Ph.D., Horticulturist in
Charge
E. G. Kelsheimer, Ph.D., Entomologist
F. T. McLean, Ph.D., Horticulturist
A. L. Harrison, Ph.D., Plant Pathologist
David G. Kelbert, Asst. Plant Pathologist
E. L. Spencer, Ph.D., Soils Chemist

Sanford
R. W. Ruprecht, Ph.D., Chemist in Charge
J. C. Russell, M.S., Asst. Entomologist

Lakeland

E. S. Ellison, Meteorologist2 6
Warren 0. Johnson, Meteorologist'

1 Head of Department.
SIn cooperation with U. S.
3 Cooperative, other divisions, U. of F.
SIn Military Service.
5 On leave.

















CONTENTS


INTRODUCTION ...... .. ........ -- .......- ........... ......

LOSSES DUE TO PHYSICAL FACTORS ...............................
Lack of W ater -........ ... .................----
Excess of W ater --. ............... ..-----. -
High Temperatures .............-..--- .. ...-.-------- --------
W ind and Rain ......................-.-.. ... ....-- -------.- -----
Sunning ..... -.. ... .......-...------------ ---- --
Fertilizer Injury ...------ -- .------------ -----
Chemical Injury ..................... .....--.---. -------------- -
Premature Seeding or "Bolting" .......... .......-- ------------

DAMPING-OFF ..-.-.. --.....--- ......----- -- --- .----------.---------
Importance of the Disease ... ---..-.............---.-. ------
Signs and Symptoms of the Disease .......--....
Cause of Damping-off ........ --.... --..------ ---.--- --.---.--
Secondary Factors in the Development of Damping-off .......-
Control of Damping-off ............. .. .... -...---- .. ---- ----
Seed Treatments ............ --...-...........---
Soil Treatments ----.. .... ---------... .--------
Plant Treatments .....................
Combination of Treatments ...........--.. --..-..------- ---
Cultural Practices Affecting Damping-off .....-------------------
CONTROL OF OTHER DISEASES AND INSECTS .........-.---------
Early Blight ........ ...-- .-. .... .
Late Blight -....-..--- ----..~ ......---- ---
Virus Diseases and Aphids ...............-....- ----- ----
Cutworms ...........-..-.. ..-- ...... ---- ------- -----
Root-knot ............ ...... ----.. -.-. .- .. --------- ----- ---
DISCUSSION ..........-........... ---.....-..


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CONTROLLING DAMPING-OFF AND OTHER LOSSES IN
CELERY SEEDBEDS

G. R. TOWNSEND

INTRODUCTION

Many fungicides have been tested for the control of Rhizoc-
tonia damping-off in celery seedbeds at the Everglades Experi-
ment Station from 1936 to 1943. In the course of these experi-
ments much has been learned about the control of damping-off
and other losses which occur in celery seedbeds on peat soils. It
is thought that the tests with certain materials and practices are
sufficiently conclusive that definite recommendations can be
made. The suggestions are largely based on some very extensive
experiments conducted in 1942, a year when Rhizoctonia damp-
ing-off caused losses up to 95 percent in unprotected seedbeds.
The 1942 experiments were statistically significant, and were
confirmed by growers' tests and further experiments in 1943.
Celery plants for the winter and spring crops in Florida are
started in outdoor beds from July to December. The seed is sown
on the surface of beds of well prepared soil. These are raised
to prevent flooding by heavy rains and are surrounded with chan-
nels into which irrigation water is pumped. A high water table
is maintained until the young plants are well rooted. The beds
are shaded with muslin covers (Fig. 1) to protect the young
plants from the sun and rain. Cloths 72 inches wide and weigh-
ing 4 ounces per yard are stretched over A frames or other sup-
ports. Various arrangements are employed for fastening the
cloth and for lifting it to permit sunlight to reach the plants as
they grow older.
The customary practice is to construct beds 50 or 100 yards
long by 4 feet wide. Fertilizer is broadcast over the surface of
the bed and mixed with the soil to a depth of 2 inches. For peat
soils in the Everglades 20 to 60 pounds of an 0-8-24 mixture is
applied to a 1,200 square foot seedbed. Seedbeds on sandy soils
in other parts of the state may be fertilized with a 4-8-4 or 4-9-3
mixture at 40 to 100 pounds per 1,200 square feet. Several top-
dressings of mixed fertilizer, nitrate of soda or nitrate of potash
may be applied to seedbeds on sandy soils.
The seedbeds should be fertilized and carefully levelled several
days in advance of sowing. Most growers broadcast 4 to 6







Florida Agricultural Experiment Station


ounces of seed over 1,200 square feet of bed, however 2 ounces
of good seed is enough when the beds are properly managed. A
few growers soak their seeds and have them partially sprouted
when sown.
The shade cloth should be put down and irrigation started as
soon as the seeds are sown. In some sections the seeds are cov-
ered with burlap sacking until they sprout. The soil surface is
kept wet by the capillary movement of water from the irrigation
channels during the period when the seeds are sprouting. Irri-
gation is continued until the plants have taken root and spread
their cotyledonary leaves.
Sprouting of the seed occurs in from 5 to 14 days, depending
on the temperature and on the vitality of the seed. The plants
become established rapidly in the warmer months, but grow very
slowly after the weather is cooler.
The plants remain in the seedbeds for 8 to 10 weeks. It is a
general practice to cut the tops of the plants with trimming
shears at least once before transplanting. This makes the plants
stocky and more easily handled in the transplanting machines.

LOSSES DUE TO PHYSICAL FACTORS
LACK OF WATER
A moist soil is essential for the sprouting of celery seed. It
has been noted that very slight differences in the level of the
beds may cause portions of the soil to be too dry for the seed to
germinate. The water level should be sufficiently high to keep
the entire soil surface wet by capillarity. The proper level for
water to be held will vary with the type, texture and compactness
of the soil, and with the season, since evaporation dries the sur-
face much faster in August than in December. Good germina-
tion has been secured with the water level 3 inches below the sur-
face of muck soil during August in southern Florida. Lack of
water is often responsible for the failure of seedlings to take
root after they have sprouted. If the soil surface becomes dry
the tender roots wither before they penetrate the soil.

EXCESS OF WATER
An excessively high water level may flood the sides of the beds
and surface areas that are slightly low. Seeds may be carried
away by the movement of water over flooded areas, or they may
be prevented from germination on excessively wet spots. Failure
to germinate may be due to a lack of oxygen in saturated soil or







Controlling Do i, pii',l-ff


to the decay of seeds attacked by soil organisms. The relation
of excessive moisture to damping-off will be discussed in detail
in a later paragraph.
HIGH TEMPERATURES
Temperatures of the air and soil under the shade cloth some-
times are too high for the seed to germinate. This is most likely
to occur in July and August when outside air temperatures may
exceed 95' F. Seed which germinates poorly in August on
account of the hot weather may germinate well in October.
Some growers use 2 shade cloths over their early beds because
they obtain more plants in this way. Tests have shown that
double shades reduce the passage of light and heat. On a test
bed in August 1941 the passage of light through a double shade
was reduced to 7 foot-candles when 48 foot-candles of light passed
through a single shade. Soil temperatures were from 4 to 9 F.
lower under the double shade, and the stand of plants was 45
percent higher. It also is a common experience that the outside
bed, in a series of 15 or 20, frequently will show the best germi-
nation and growth of plants. This is particularly true of those
with an eastern exposure which are cooled by the prevailing
easterly winds.
WIND AND RAIN
It is necessary to protect the plants from heavy summer show-
ers, especially showers accompanied by wind. Wind and rain will
beat the seed and small plants into the soil and will damage them
beyond recovery. Larger plants will be beaten down and many
will damp-off if they are not protected by shade cloths. During
periods of dry weather there have been losses of seed and young
plants on beds that were built with a slight crown. Even mod-
erate breezes blowing over such beds will remove seed and whip
young plants with pellets of muck or sand blown along the soil
surface. This type of loss can be controlled by the proper level-
ing of the bed and by keeping the surface soil moist enough to
prevent the wind from moving it.
Plants are sometimes lost when the wind whips frayed portions
of the shade cloth across the beds. The shade cloth should be
kept in repair and securely fastened to prevent this damage.

SUNNING
Celery plants that have been grown under shade cloth must
be exposed to the sun carefully for some time before transplant-







Florida Agricultural Experiment Station


ing. This is very important for the early beds. Plants that are
exposed to the full sun too quickly after shading will become
chlorotic and stunted. Some plants may be lost by over exposure
but the principal damage comes from delaying the growth of
plants intended for an early crop. If double shades have been
used it is best to remove one cloth when the first pair of true
leaves have unfolded. Starting a few days later the other cloth
should be lifted for a few hours each morning, preferably leaving
a western or northern exposure. After a few days of gradually
lengthened exposure the cloth may be left up all day, but should
be dropped during storms.

FERTILIZER INJURY
A loss of plants resembling damping-off sometimes occurs on
beds that have been improperly fertilized. The plants become
chlorotic and their roots turn brown. Some plants recover by
putting out new roots but these are not desirable for transplant-
ing to the field. Fertilizer injury of this character is generally
associated with long periods of hot, dry weather. Plants in the
centers of the beds often are affected by this injury while the
plants along the edges are not injured (Fig. 2).







.4.I













Fig. 2.-A concentration of salts from the soil solution and from ferti-
lizers applied to the seedbed sometimes prevents the development of plants
in the centers of the beds.







Controlling Damping-off


Fertilizer injury occurs where the beds have been fertilized
too heavily or where the distribution of fertilizer is uneven due
to careless application and poor mixing with the soil. Sowing
the seed too soon after applying the fertilizer also may result in
this type of loss.
Capillary movement of water brings all soluble salts to the
surface of the bed where they become concentrated by evapora-
tion. Such concentrations become particularly troublesome in
hot, dry weather, especially after irrigation has been discontin-
ued. Tests' have shown that potash alone may reach a surface
concentration in muck soils equivalent to 1,200 pounds per acre
where plants exhibit symptoms of injury, while the soil around
nearby healthy plants would contain less than half as much
potash.
Water levels during the period of irrigation have considerable
influence on the accumulation of potash in the surface soil. The
data in Table 1 were secured on a replicated series of plots in
August 1942. Potash had been applied to these plots at the
rates of 175 and 350 pounds per acre a month before the tests
were made. Where the water level was held 3 inches below the
surface the concentration of potash in the surface soil had in-
creased more than 300 percent. However, with a 1-inch water
level, potash had not accumulated.

TABLE 1.-INFLUENCE OF CULTURAL PRACTICES UPON THE CONCENTRATION
OF POTASH IN THE SURFACE INCH OF SEEDBED SOIL.*
Water level at Amount of 0-8-16 Accumulation
fertilizer per of potash
1200 square feet. Lbs. per A.
3 inches ........... ... .............. 30 lbs. 552
3 inches ....................................60 lbs. 1,163
1 inch ................................... 30 lbs. 254
1 inch .................-................... 60 lbs. 288
minimum significant difference 191
*Chemical data by courtesy of Dr. W. T. Forsee.

Fertilizer injury can be prevented by limiting the amount of
fertilizer applied on muck soils to 20 pounds per 1,200 square feet
and by more careful attention to its distribution on the bed.
Maintaining a high water level while irrigating will tend to
reduce the surface concentration of all soluble salts which might
be injurious. Overhead irrigation of the beds may be used to
lower surface concentrations of salts that have accumulated

1 Analyses of soil samples were made by W. T. Forsee.






Florida Agricultural Experiment Station


during dry weather, but this practice should be followed with a
fungicide treatment to prevent damping-off.
CHEMICAL INJURY
Concentration of chemicals other than fertilizers will also
damage young plants. Usually this type of injury follows the
use of excessive amounts of fungicides, or planting too soon
after soil treatments with such materials as formadehyde and
chlorpicrin.
PREMATURE SEEDING OR "BOLTING"2
Plants in seedbeds are quite often injured by relatively low
temperatures, although the injury is usually apparent only as the
crop approaches maturity. Premature seeding or "bolting" occa-
sionally causes serious losses in all celery growing areas of the
state with the exception of the Everglades. This loss may be
greatly reduced and in many instances prevented by protecting
the plants in the seedbeds from exposure to low temperatures.
Premature seeding of celery is caused by exposure of the crop
to relatively low temperatures for an extended period. Young
plants of seedbed size require less exposure to cold for initiation
of the seed stalk than do older plants. Thus, exposure of seed-
beds to a continuous temperature of 500 F. or lower for a period
of 10 days or longer is sufficient in most varieties to initiate seed
stalks. Some varieties are more resistant to low temperature
but all varieties are susceptible if exposure is sufficient.
After the seed stalk is initiated, good cultural treatments will
only hasten the development or appearance of the seed stalk.
Thus every effort should be made to protect plants of seedbed
size from exposure to temperatures below 500 F. for a consider-
able period. This may be accomplished in certain instances by
lowering the covering over the bed earlier in the evening, by
adding an extra cover or, if necessary, by using smudge pots or
other methods of heating. A thermograph or a daily record of
maximum-minimum temperatures will be of much assistance to
growers in determining when special protection of their beds is
necessary.
DAMPING-OFF
IMPORTANCE OF THE DISEASE
Damping-off is the principal cause of losses occurring in celery
seedbeds. It is particularly serious in beds sown during the sum-
Contributed by F. S. Jamison.






Florida Agricultural Experiment Station


during dry weather, but this practice should be followed with a
fungicide treatment to prevent damping-off.
CHEMICAL INJURY
Concentration of chemicals other than fertilizers will also
damage young plants. Usually this type of injury follows the
use of excessive amounts of fungicides, or planting too soon
after soil treatments with such materials as formadehyde and
chlorpicrin.
PREMATURE SEEDING OR "BOLTING"2
Plants in seedbeds are quite often injured by relatively low
temperatures, although the injury is usually apparent only as the
crop approaches maturity. Premature seeding or "bolting" occa-
sionally causes serious losses in all celery growing areas of the
state with the exception of the Everglades. This loss may be
greatly reduced and in many instances prevented by protecting
the plants in the seedbeds from exposure to low temperatures.
Premature seeding of celery is caused by exposure of the crop
to relatively low temperatures for an extended period. Young
plants of seedbed size require less exposure to cold for initiation
of the seed stalk than do older plants. Thus, exposure of seed-
beds to a continuous temperature of 500 F. or lower for a period
of 10 days or longer is sufficient in most varieties to initiate seed
stalks. Some varieties are more resistant to low temperature
but all varieties are susceptible if exposure is sufficient.
After the seed stalk is initiated, good cultural treatments will
only hasten the development or appearance of the seed stalk.
Thus every effort should be made to protect plants of seedbed
size from exposure to temperatures below 500 F. for a consider-
able period. This may be accomplished in certain instances by
lowering the covering over the bed earlier in the evening, by
adding an extra cover or, if necessary, by using smudge pots or
other methods of heating. A thermograph or a daily record of
maximum-minimum temperatures will be of much assistance to
growers in determining when special protection of their beds is
necessary.
DAMPING-OFF
IMPORTANCE OF THE DISEASE
Damping-off is the principal cause of losses occurring in celery
seedbeds. It is particularly serious in beds sown during the sum-
Contributed by F. S. Jamison.







Controlling Damping-off


mer and at times may destroy as much as 95 percent of the
plants. As an average for the season a loss of 25 percent of the
plants should be expected if control measures are not employed.
This loss increases the cost of production of celery by $10.00 to
$25.00 per acre. Further losses are brought about indirectly by
the practice of sowing more seed than is desirable if all the
plants live, and by the loss of some transplanted plants which
were infected before being pulled from the seedbeds. Stalk rot
due to Rhizoctonia attacking mature celery also may be due in
part to transplanting infected plants.

SIGNS AND SYMPTOMS OF THE DISEASE
The root tips of recently sprouted celery plants may turn
brown and decay before they enter the soil. This is a less fre-
quent development than the loss of plants which have already
taken root and begun to grow. Usually the disease is first
noticed when individual plants, widely scattered or in groups,
begin to topple over and wither. A considerable loss of plants
prior to the unfolding of the first true leaves may go undetected
if the infected plants are widely scattered. However, if groups
of plants are infected the appearance of bare spots on the seed-
bed soon will be detected. These bare spots may be only 1 or 2


Fig. 3.-Two circular areas in which the plants were damping-off have en-
larged and merged to form an irregular area on which all plants are dead.







Florida Agricultural Experiment Station


inches in diameter to begin with, but if favorable conditions pre-
vail they will enlarge daily until they reach diameters of 12 to 30
inches (Fig. 3) or until several such spots have merged and the
bed is covered with withered and dried plants, lying prostrate
on the soil.
During periods of high humidity and high temperatures the
thread-like mycelium of the fungus which causes this disease
may be seen as a growth resembling a spider-web on the surface
of the soil around affected plants. The mycelium develops par-
ticularly well on humid nights and can be seen in the morning
covering the soil in damped-off areas and extending a few inches
into areas of plants that are still standing. The plants in the
area covered by the fungus will be found to have water-soaked
stems and usually these plants wilt as soon as the humidity de-
creases. The mycelium of the fungus dries up during the day
unless it is cloudy and very humid.
CAUSE OF DAMPING-OFF
Damping-off of celery in Florida is caused by the parasitism of
a number of species of fungi, chiefly Rhizoctonia solani Ktihn.
This is a soil-inhabiting fungus which is capable of living as a
saprophyte on organic debris in the soil, or as a parasite attack-
ing the seeds, roots, stems and even the leaves of many species
of plants which come in contact with the soil. The fungus does
not produce spores, but is widely disseminated by portions of the
mycelium which break off and are carried by wind, water, soil
or infected plants. This fungus sometimes produces sclerotia
which are minute tuberous tissues capable of withstanding very
unfavorable conditions and which preserve the fungus in the soil
when conditions do not favor its growth.
SECONDARY FACTORS IN THE DEVELOPMENT OF DAMPING-OFF
The development of damping-off depends primarily upon the
presence of Rhizoctonia, or sometimes other fungi, in soil. Fac-
tors which contribute to heavy losses from damping-off are
highly contaminated soil, humid conditions and high tempera-
tures. The disease seldom causes much loss in seedbeds on newly
cleared muck soils, but becomes more prevalent where the soils
have been cultivated longer. This is particularly true where the
same soil area has been used for celery seedbeds for a number of
years,
The role of humidity in promoting damping-off is so important
that it has been recognized in naming the disease. Outbreaks







Controlling Damping-off


of damping-off occur during prolonged periods of high humidity
and reach their maximum intensity when a few cloudy and rainy
days occur during periods of high temperature. Losses from
damping-off are highest in August and September, when temper-
atures above 75 F. prevail, and are reduced sharply with the
advent of cooler and drier weather in October.
Crowding of the plants contributes to the development of
damping-off. The humidity is higher under a mat of crowded
plants than it is where more light and air penetrate to the sur-
face of the bed. When damping-off starts in crowded beds the
fungus develops a vigorous mycelium on the mat of dead plants
within the affected areas and attacks nearby plants. When
crowded plants are clipped the leaves falling around the plants
sometimes become infected and promote damping-off.

CONTROL OF DAMPING-OFF
Seed Treatments.-Seed treatments have been found to be
ineffective for the control of damping-off. While protective fun-
gicides applied to the seeds undoubtedly prevent the decay of
many seeds, the protection does not extend to the plants beyond
the period of 1 or 2 weeks after they have taken root. Treatment
of the seed with spergon or semesan dusts, or with a 1:2,000
mercuric chloride solution for 10 minutes, reduces the loss in the
very young plants but fails to control the disease as the plants
grow larger. The amount of fungicide carried by a few ounces
of seed is not enough to have much influence on pathogenic fungi
in seedbed soils.
Soil Treatments.-Sterilization of the seedbed soil by the use
of steam or chemicals would control damping-off. Complete
sterilization of the soil has not been attempted because of the
costs of chemicals or of the equipment for steam treatment.
Various methods of partial sterilization of the soil have been
tried with the hope that the pathogenic fungi in the soil would
be sufficiently inhibited to permit the development of healthy
celery plants.
Formaldehyde has been used for many years as a soil steriliz-
ing agent. The standard recommendation is to apply 1/9 gallon
of a 1:50 solution to each square foot of soil. It is also recom-
mended that the treated soil be covered to retard the escape of
the fumes. This treatment appeared to be too expensive to meet
the needs of celery growers. Modifications of it which would be
less expensive have been tested annually for 7 years. In some







Florida Agricultural Experiment Station


seasons considerable success has been obtained by sprinkling the
soil with 1:50 formaldehyde solutions at rates of 1 gallon per 2
square feet to 1 gallon per 8 square feet. The solution was ap-
plied with sprinkling cans and incorporated in the surface 3
inches of soil by chopping with rakes. The seeds were sown
10 to 14 days later when the odor of formaldehyde could not be
detected in the treated soil. These treatments reduced the loss
from damping-off during sprouting and the early growth of the
plants. Plants on formaldehyde-treated soil grew faster and were
greener unless they became too crowded. However, in some sea-
sons when conditions were favorable for damping-off there were
losses even on treated beds. In most seasons more plants were
obtained from the treated plots than from untreated plots. The
data in Table 2 were obtained in 1942 and are typical of results
with formaldehyde soil treatments for other years. The treat-
ment is not recommended highly.
Various formaldehyde dust preparations have been tried as
soil treatments. None of these has been found to be effective
when quantities of dust which would be economical have been
used.
Chlorpicrin is difficult to handle because of its irritating prop-
erties. Treatment is accomplished by injecting a few cubic cen-
timeters of the liquid into each square foot of soil. Injections
should be made with special apparatus to a depth of 3 to 5 inches.
The liquid volatilizes readily and it is necessary to retard the
escape of the gas from the soil by sealing with gas-proof paper
or by thoroughly wetting the surface soil. Seeds must not be
sown until the gas has escaped from the soil.
In these experiments chlorpicrin was injected at rates of 1 to 5
cc. per square foot. One cubic centimeter per square foot is equal
to a dosage of 160 pounds per acre or 4.3 pounds per 1,200 square
feet. In 1940 chlorpicrin injected at 3 cc. per square foot greatly
improved the growth of celery plants and prevented minor losses
from damping-off. Plants on the chlorpicrin plot were more
numerous and were larger and healthier than on the untreated
soil. Other tests have indicated that the stimulation observed
here was due to effects on the microflora and the availability of
certain nutrients. Injections of 1, 1.5 and 2.7 cc. per square foot
in 1941 were ineffective in preventing a severe outbreak of damp-
ing-off 8 weeks after the soil had been treated, although earlier
there had been indications that the disease was being controlled.
Results with chlorpicrin in 1942 are shown in Table 2. The dis-















TABLE 2.-EFFECT OF SOIL TREATMENTS ON THE DEVELOPMENT OF DAMPING-OFF OF CELERY PLANTS IN 1942.


Soil Treatment per 1,200 Square Feet


Spergon-6 pounds ........................................
Formaldehyde-1:50 600 gal ......................
Cuprocide-6 pounds .....................................
Chlorpicrin-5 cc. per sq. ft. .........................
Fermate**-6 pounds ..................................
Ceresan-1 pound ......................................
Thiosan**-6 pounds ....... .....................-...
N on e ................ ..... ... ...... ........


Minimum significant difference .......................


Average Number of Damp-off
per 50 Square Feet on*
8/28 8/31 9/4


5.00
1.75
10.25
2.50
2.00
8.00
2.75
9.75


Areas

9/8

11.50
2.25
15.25
4.75
4.50
11.75
5.25
14.25


n.s. 1.35 4.41 4.85


Percent Damp-off on
9/12 9/17 10/12


26.75
11.75
53.75
17.50
5.50
37.50
7.50
53.75


60.00
17.50
70.00
27.50
13.75
61.25
23.75
73.75


83.75
46.25
86.25
45.00
41.25
81.25
45.00
86.25


26.50 24.14 13.48


*Averages for 4 plots.
**Injurious.







Florida Agricultural Experiment Station


ease was retarded in development and loss of plants was
restricted by 50 percent where chlorpicrin had been injected at
the rate of 5 cc. per square foot. The evidence from the tests
during 3 seasons is that the soil becomes recontaminated too
rapidly following chlorpicrin treatments. Apparatus for more
effective treatment of the soil with chlorpicrin is being developed
by the manufacturers.
Ceresan (5 % ethyl mercury phosphate) was applied in solution
prior to seeding. It was found that as much as 1 pound of cere-
san applied per 1,200 square feet may be injurious to the germi-
nation and growth of plants. In 1942 this treatment (Table 2)
did not control damping-off.
Yellow cuprocide (93 percent cuprous oxide) was tested as a
soil treatment and was found unsatisfactory. In 1936, when it
was applied at the rate of 3 pounds per 1,200 square feet, damp-
ing-off was not controlled and the yield of plants was 21 percent
lower than from untreated soil. In 1942 (Table 2) cuprocide was
applied at the rate of 6 pounds per 1,200 square feet and failed
to have any influence on damping-off. This is in contrast with
good results obtained with the same material applied as a plant
spray. Apparently the cuprous oxide undergoes a reaction which
destroys its potency when mixed with the soil.
Basic copper sulphate was tested as a soil treatment only once.
In this instance it was applied at the rate of 5 pounds per 1,200
square feet. Damping-off was so severe on a single plot treated
with this material that it contained only 20 percent as many
plants as did an untreated plot.
Spergon (tetrachloroparabenzoquinone) was applied to test
plots as a soil treatment in 1942 at the rate of 6 pounds per 1,200
square feet. Damping-off developed at a somewhat slower rate
on the spergon-treated plots but the differences (Table 2) were
insignificant. It should be pointed out that these results are not
in agreement with those where spergon was used as a plant
spray.
Fermate (ferricdimethyldithiocarbamate) and thiosan (tetra-
methylthiuramdisulphide) were applied to the soil at the rate
of 6 pounds per 1,200 square feet in the 1942 experiment. Both
materials proved to be injurious to celery plants at this rate of
application. The plants failed to take root in spots where these
chemicals were concentrated by uneven distribution. Some
plants which started to grow later became chlorotic and withered.
In parts of the bed where the concentration of these chemicals















TABLE 3.-EFFECT OF SPRAY TREATMENTS ON THE DEVELOPMENT OF DAMPING-OFF OF CELERY PLANTS IN 1942.


Spray Treatment


Cuprocide-% lb. to 50 gal .....
Bordeaux**-4-2-50 -...........
Spergon-2 lbs. to 50 gal .......
Fermate--1 lb. to 50 gal ......
Ceresan**-21/2 oz. to 50 gal.
Sulphur-6 lbs. to 50 gal .........
Thiosan--/2 lb. to 50 gal. .......
N on e ........ .... .............


Minimum significant difference


Average Number of Damp-off Areas
per 50 Square Feet on*
S 8/28 8/31 9/4 9/8


0.25
0
0
0.75
0
6.25
2.25


0.50
0
0
2.00
0
14.00
3.25


0.25 1.50 17.25 21.25


n.s. 1.23 2.75 2.70


Percent Damping-off on
9/12 9/17 10/12


0.50
0
0
0.50
0
15.00
1.00
71.25


0.50
0
0
0.50
0
42.50
2.25
90.00


5.00
0
0
10.00
0
45.00
12.50
95.00


5.49 5.68 5.49


*Averages for 4 plots.
**Injurious.








Florida Agricultural Experiment Station


Fig. 4.-The well spaced plants on this bed have been protected from
damping-off by the application of fungicidal sprays and dusts.


Fig. 5.-Several well managed seedbeds after the shade cloths have been
removed.







Controlling Damping-off


was not too high the plants grew well and were protected from
damping-off during the first month. Some damping-off occurred
on these plots during the second month (Table 2). It is possible
that these materials could be used safely at somewhat lower dos-
ages if care is taken to insure even distribution of the chemicals.
However, the data indicate that both materials break down too
soon to protect the plants through the entire seedbed period.
Semesan (30 percent hydroxymercurichlorphenol) applied at
the rate of 1 pound to 1,200 square feet reduced the number of
plants by 17 percent on 2 plots in the 1936 experiment.
Plant Treatments.-Applications of fungicides as dusts or
sprays to the young plants should be started after they take root
and before damping-off occurs. Usually it is necessary to repeat
these treatments at intervals of 4 to 7 days during periods when
damping-off is most active. Plant treatments have the advan-
tage of being not only the simplest type of treatment but also
are the most effective and least expensive treatment so far devel-
oped (Figs. 4 and 5). The data from an experiment in 1942 are
shown in Table 3.
In the 1942 seedbed experiments fermate was applied as a
plant spray to a series of plots. Six applications were made dur-
ing the period from August 27 to September 23. About 15 gal-
lons of spray were required to cover 1,200 square feet at each
application. The fermate spray carried 1/ pound of the com-
pound in 50 gallons of water for the first application and 1/
pound to 50 gallons thereafter. The data in Table 3 show that
damping-off was controlled very effectively until October. The
plants were so thick at the time of the last application that the
spray did not penetrate well and some damping-off developed
late in the season. A supplementary test showed that this late
development could be checked by drenching the beds with a fer-
mate solution applied with a sprinkling can. The larger volume
of water carried the fungicide to the soil where it is effective in
checking damping-off.
Fermate was also tested for the protection of celery plants
in seedbeds by growers in 1942. Fermate may be applied either
as a dust or by spraying or sprinkling the beds. Several growers
obtained very good results by applying a 10 percent dust at rates
varying from 1/2 to 1 pound of the dust to 1,200 square feet.
There was no injury from this amount of dust evenly distributed.
Damping-off was very effectively controlled by dusting while the
plants were small. Before the plants were ready to transplant







Florida Agricultural Experiment Station


they formed a mat of leaves so thick that the dust did not reach
the soil where it must be deposited to be effective. Growers
found spraying and sprinkling were more effective methods of
application as the plants grew larger and formed a mat of leaves
over the soil.
Thiosan was tested as a plant spray and gave results approx-
imately similar to those obtained with fermate when used at the
rate of 1/2 pound to 50 gallons of water. The data indicate that
it was highly effective for controlling damping-off (Table 3).
The tolerance of the plants for thiosan was somewhat less than
for fermate.
Spergon proved to be highly effective in the 1942 experiments.
Six applications of 2 pounds of spergon in 50 gallons of spray
gave complete protection from damping-off when 95 percent of
the plants on check plots damped-off. Spergon was effective over
a longer period than other compounds, since no damping-off de-
veloped on the plots between the date of the last application on
September 23 and the date of the final records, October 12.
Spergon was less desirable as a spray during the early growth of
the plants because it stunted and slightly hardened them. This
effect disappeared as the plants grew older and they were normal
when they were ready for transplanting. The slightly injurious
effect on the young plants can be avoided by reducing the dosage
to 11/2 pounds per 50 gallons for the first 3 applications.
Yellow cuprocide proved to be an effective plant spray in the
1942 experiment. Previous experience with this material had not
been entirely satisfactory, although this is now believed to have
been due to insufficient or untimely applications. There were
no significant differences between the results with cuprocide at
/4 pound to 50 gallons and several other compounds in 1942.
Cuprocide stunted the young plants slightly but not seriously.
Bordeaux mixture (4-2-50) proved to be very damaging to
young celery plants in 1942. The plants were very chlorotic and
stunted while young, but those which survived the injury grew
well after the last application of bordeaux. There was no loss
from damping-off on plots sprayed with this fungicide.
Ceresan was tested as a plant spray for several years. It gave
good results when 1 or 2 applications sufficed to control damping-
off. However, in a season when the disease was very active
this organic mercury compound became injurious when many
applications were made. In the 1942 experiments the plants
sprayed with ceresan at 21/ ounces to 50 gallons became chlo-














TABLE 4.-EFFECT OF COMBINATIONS OF SOIL AND SPRAY TREATMENT ON THE DEVELOPMENT OF DAMPING-OFF OF CELERY
PLANTS IN 1942.


Soil Treatment-Plant Treatment


Thiosan-Thiosan** ...... .. ....... .......
Spergon-Spergon .................. ...... .....
Cuprocide-Cuprocide .. ........-..............
Fermate-Fermate** --......................
Ferm ate-Thiosan** .............. .........
Thiosan-Fermate -----.. ... ..............
Formaldehyde-Thiosan .....------------............
None .......... .. ..................................


Minimum significant difference ............-..

*Averages for 4 plots.
**Injurious.


Average Number of Damp-off Areas
per 50 Square Feet on*
8/28 8/31 9/4 9/8

0 0.50 1.50 1.50
0.25 0.25 0 0
1.50 2.75 2.00 2.00
0 0 0 0
0 0 0.25 0.25
0.25 1.00 0.50 2.00
0 0.75 1.50 2.50
0.50 3.50 18.50 22.50


0.87 1.77 2.37 5.39


Percent Damp-off on
9/12 9/17 10/12


1.50
0
0
0
0.50
0.50
2.25
80.00


0.50
0
0.25
0
0
0.75
2.25
94.00


3.25
0
1.50
0.75
3.25
3.75
25.75
96.25


10.58 3.68 9.05







Florida Agricultural Experiment Station


rotic, spindly and prostrate after the third application. Damp-
ing-off did not occur on the treated plots in this experiment,
although it has been known to occur on ceresan-treated beds if
the treatment is not repeated frequently.
Wettable sulphur is not an effective fungicide for controlling
damping-off. Plots sprayed with this material at 6 pounds to 50
gallons developed about half as much damping-off as untreated
plots showing losses of 95 percent.
Combination of Treatments.-Tests of certain combinations
of treatments were made in 1942. The data in Table 4 show the
results that were obtained. In most instances there was no
advantage in using a soil treatment prior to seeding and follow-
ing that with a spray treatment of the young plants. The com-
bination of the formaldehyde soil treatment and the thiosan
plant treatment looked very good for several weeks. There was
a better stand of plants and a more rapid development of the
plants with this combination. However, growth on these plots
became so heavy that it was difficult to apply the thiosan effec-
tively. After this occurred there was some development of
damping-off but less than where formaldehyde had been the only
treatment used.
Cultural Practices Affecting Damping-off.-Observations over
a period of several years suggested that certain cultural prac-
tices influenced the development of damping-off. An experiment
testing the effects of shading, fertilization and water level on
the development of damping-off was conducted in 1942. No pro-
tective fungicides were applied in this experiment and, yet, as
the data in Table 5 show, certain practices very materially re-
tarded the development of damping-off. The use of double shades
over the beds during the first month reduced the loss from damp-
ing-off by 36 percent. Plots on which the water level never rose
above 3 inches from the surface had 22 percent more plants than
where the water level was allowed to rise as high as 1 inch from
the surface. Highly fertilized plots had somewhat less damping-
off than plots with a normal rate of fertilization. The interac-
tions of these factors (Table 6) resulted in the lowest loss from
damping-off where double shades, a low water table and a high
rate of fertilization were employed. There was 76 percent more
damping-off where the alternative combination of treatments
was used.
Growth and development of the plants were retarded by the
practices that retarded the disease. Consequently, these prac-













TABLE 5.-EFFECT OF VARYING CULTURAL PRACTICES ON THE DEVELOPMENT OF DAMPING-OFF OF CELERY PLANTS IN 1942.

Average Number of Damp-off Areas Percent
Treatment per 50 Square Feet on* Damp-off on
8/28 9/8 9/17 ^

Single shade .................. .... ....................... ......... 1.75 14.00 91.43
Double shade .---........------ ..... ........................... 0.31 6.50 55.18


W ater at 3-inch level .............................................. 1.56 9.37 62.06
W ater at 1-inch level ................... ....................... 0.80 11.87 84.56


30 lbs. fertilizer per 1,200 sq. ft. ................. 1.31 12.25 78.37
60 lbs. fertilizer per 1,200 sq. ft. --.....- 0.87 9.00 68.25


Minimum significant difference ...................... ...... 0.94 1.60 7.19
*Averages for 4 plots.



















TABLE 6.-EFFECT OF THE INTERACTION OF 3 FACTORS ON THE DEVELOPMENT OF DAMPING-OFF OF CELERY PLANTS IN 1942. ;.


S Fertilizer
Shade Water 0-8-16 per Average Number of Damp-off Percent Damp-off on
Cloth Level 1,200 Square Areas per 50 Square Feet on* 9/17
Feet 8/28 9/8

Single 3 inch 30 lbs. 4.00 15.50 95.25
Single 3 inch 60 lbs. 1.75 10.50 95.50
Single 1 inch 30 lbs. 0.75 9.00 91.25
Single 1 inch 60 lbs. 1.00 9.00 83.75
Double 3 inch 30 lbs. 0.25 3.00 42.50
Double 3 inch 60 lbs. 0.25 0.25 15.00
Double 1 inch 30 lbs. 0.25 11.25 84.50
Double 1 inch 60 lbs. 0.50 5.75 78.75


0

59-


S
n
-i
59

n3


Minimum significant difference .......


n.s.


3.59


*Averages for 4 plots.


14.39
5-
0e







Controlling Damping-off


tices cannot be relied upon as the sole means of disease control.
It would be advisable to protect the early beds with double shades
until the first true leaves unfold. One shade then should be
removed and the plants gradually hardened by lifting the other
shade a few minutes longer each day. Water level cannot be
employed effectively to reduce damping-off because of the danger
of fertilizer injury during periods of hot and dry weather if the
water level is too low. The same is true of high rates of fertili-
zation.
CONTROL OF OTHER DISEASES AND INSECTS
EARLY BLIGHT
This disease, caused by Cercospora apii Fr., sometimes affects
celery plants in the plant bed. Early blight is controlled more
easily in the field if the plants in the seedbed have been protected
by spraying. Since the disease can be controlled with fermate,
spergon or cuprocide sprays, no additional treatments for early
blight should be necessary when 1 of these materials is used as
a plant treatment for damping-off control.

LATE BLIGHT
The diseases caused by Septoria apii (Br. and Cav.) Chester
and S. apii-graveolentis Dorogin are seed-borne and must be
controlled in the seedbed if satisfactory control in the field is
expected. Fortunately, the black pycnidia of the late blight fungi
can be detected on the seed and infected seed can be treated in
hot water at 1180 F. for 30 minutes. This treatment should be
used on all infected seed sown late in the fall for a spring crop.
It is not so necessary for the early plantings, since the tempera-
tures in the early fall probably are too high to permit infection
of the plants.
Spraying the seedbeds for the control of damping-off and early
blight also will aid in the control of late blight. If the disease
is not controlled in the seedbed it would be better to destroy the
plants than to plant them in the field where control would be
very difficult and other plantings would be exposed to the late
blight diseases.
VIRUS DISEASES AND APHIDS
Virus diseases of celery are becoming of increasing importance
in Florida. These diseases, of which mosaic is an example, are
caused by the transfer of sap from virus-infected weeds to the
celery by several species of aphids. The problem of virus disease







Florida Agricultural Experiment Station


control so far as it relates to seedbeds resolves itself into the con-
trol of all aphids and the destruction of weeds in and around
the seedbed area. Aphids can be controlled by nicotine-contain-
ing insecticides, or by rotenone sprays when available. Weeds
should be controlled by hand work in the beds and by cultivation,
burning or weed-killing sprays over an area at least 50 feet on
all sides of the seedbeds.
CUTWORMS
Cutworms sometimes are troublesome in celery seedbeds. They
are controlled by broadcasting poison bran baits early in the
evening. If the first application is not fully effective a second
should be made. Growers must watch for cutworms constantly,
as they can destroy many plants if allowed to develop.
ROOT-KNOT "
Nematodes in the seedbed soils enter the roots of the plants
and produce the galls known as root-knot. The nematode is a
very minute worm which attacks many species of plants. Affected
plants have galls on the roots, affected rootlets turn brown and
the plants become chlorotic and die. Seedbeds never should be
located on nematode-infested soil.
If clean soil cannot be obtained infested soil can sometimes be
made safe by starving out the nematodes. This can best be done
by keeping the land fallow for several months before it is to be
used for seedbeds. Flooding of fallow land for 2 or 3 months is a
good practice to follow. Nematodes which hatch in fallow or
flooded soils will starve in a few weeks because there are no
plants on which they may feed. Resistant cover crops may be
planted instead of keeping the ground fallow. However, the sys-
tem of using resistant crops requires that the soil be kept free
of weeds. A few susceptible weeds will maintain a considerable
population of nematodes.
Chemical treatment of extensive areas of soil for celery seed-
beds is not feasible because of the expense involved and the
uncertainty of most treatments now available. Improvement in
the chlorpicrin treatment and the development of new compounds
eventually may give a satisfactory chemical eradicant.
DISCUSSION
Damping-off and other losses in celery seedbeds can be con-
trolled by proper management of the beds. Great care should
'Florida Agr. Exp. Sta. Bul. 311 by J. R. Watson and C. C. Goff should
be consulted by persons desiring to control root-knot.







Controlling Damping-off


be given to leveling, fertilization and irrigation. The surface
of the bed should be raked to a level that varies by less than 1
inch to avoid fertilizer injury in the high, dry spots and damping-
off in low, wet spots. An application of 20 pounds of commer-
cial fertilizer should be adequate for a 100 yard bed (1,200 square
feet) on muck soil and, if well distributed on a properly irrigated
bed, will not result in injury to the plants. A water level 2 or 3
inches from the surface of the soil should be maintained during
the period of germination and early growth. Double shading
aids germination and growth during the warmest weather, and
damping-off is less severe where this practice is followed. The
plants will become spindly if the double shading is continued too
long. A gradual exposure to increasing amounts of sunlight is
desirable to avoid injury from too sudden an exposure to intense
sunlight.
Damping-off is most effectively controlled by the application of
certain fungicidal dusts or sprays to the plant beds at frequent
intervals during the period of greatest damping-off activity.
Materials which have been found safe and effective include fer-
mate as a 10 percent dust applied at 1/ to 1 pound per 100 yard
bed (1,200 square feet) ; fermate as a spray or drench used at
the rate of 1/ pound to 50 gallons of water; thiosan at the same
concentration; cuprocide at 3/4 pound to 50 gallons of water; or
spergon at 11/ to 2 pounds to 50 gallons. These materials when
properly applied will practically eliminate damping-off losses.
It is important that the fungicides reach the soil surface. Spray-
ing and drenching are superior to dusting after the plants form
a mat of foliage, because the fungicides reach the soil more
readily.
A consequence of securing control of damping-off is that less
seed is needed. When no loss from damping-off is expected, 2
ounces of good seed is enough for a bed measuring 1,200 square
feet. If more seed is sown the plants are likely to be spindly
because of crowding and the control of damping-off is more
difficult.
Control of early blight in the seedbed may be expected from
the plant treatments used for damping-off control. The hot water
seed treatment should be used for seed infected with the late
blight fungus. Mosaic should be controlled by destroying weed
hosts and killing all aphids. Cutworms and nematodes should be
controlled by appropriate methods.




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