C* AGRICULTURAL RESEARCH CENTER
Hastings, Florida SEP 22 1981
Hastings Research Report PR1981-8 September 22, 1981
Suni or iorioc:'
SCLEROTINIA WATERY ROT OF CRUCIFERS IN NE FLORIDA
D. P. Weingartner, Assoc. Plant Pathologist
Sclerotinia watery rot is caused by a fungus called Whetzelinia (Scerotinia)
sclerotiorum. According to Eddins' disease reports Sclerotinia watery rot was an
important disease of crucifers in the Hastings area during the 1940's and 50's.
However, during the late 1960's and early 70's the disease was relatively minor
in the area. Usually it was observed following hard freezes which injured cabbage
stems at the soil line. The fungus often grew from the soil into the injured stem
tissue causing affected plants to wilt and fall over. Adjacent healthy plants in
direct contact with those initially infected would subsequently become diseased.
During the past several seasons Sclerotinia watery rot has increased in
importance in NE Florida, particularly in Flagler County. Savoy and Abbott and
Cobb No. 5 Plus cultivars have been the most severely affected.
Although the infection of freeze injured cabbage stems from the soil was
the most frequently observed mode of infection during the 1970's, the complete
disease cycle of the fungus includes production of spores (Fig. 1). The fungus
produces masses of white growth myceliumm) on affected cabbage heads. Hard,
black-colored resting bodies (sclerotia) varying from < 1/8 to > 1.0 inch in
size are produced among the white mycelium. As the cabbage tissue decays, the
persistent sclerotia fall to the ground and are ultimately incorporated into the
soil during the disking and bedding procedures. The sclerotia can survive in
soil for long periods of time, probably years. If a period of prolonged high soil
moisture (i.e. > 10 days) follows freezing temperatures, the sclerotia buried
shallowly in the soil produce mushroom-like fruiting bodies called apothecia.
The light colored trumpet-shaped apothecia vary in size from < 1/8 to 1.5 in
length. Thousands of sticky spores are produced in each apothecium. The spores
are forcibly ejected and carried by air currents. Those spores landing on a food
base of wet, dying or injured cabbage tissue germinate and infect the tissue.
The infection then spreads slowly, mostly by plant to plant contact, from the
Careful observation of infected cabbage plants following Sclerotinia attacks
can often help determine the type of infection which occurred. When Sclerotinia
attacks cabbage plants directly from the soil without forming apothecia and spores,
most infection occurs at the soil line and on plant parts such as leaves in direct
contact with the soil. In addition, since the predisposing injury is usually
centered around a single freeze, most of the affected plants in the initial infec-
tion areas of the field have the same degree of disease. However, when apothecia
and air borne spores are produced, lesions are found on the head, wrapper leaves
and other parts of the plant which are not in direct contact with the soil.
Apparently during most seasons, only one "crop" of apothecia and spores is
produced in NE Florida. This statement is based on the observation that all
* plants in a cabbage field usually have the same approximate degree of infection.
If multiple infection periods were to occur different degrees of infection (i.e.
early to advanced) would be seen in the field. Such was the case ir 1980-81.
Different degrees of infection ranging from new lesions to completely rotted
heads were found in NE Florida cabbage fields, particularly in Flagler County.
Heavy losses were experienced by some growers.
Although direct proof are lacking, the limiting factor in NE Florida for
production of apothecia and air borne spores has most likely been the occurrence
of a freeze coupled with prolonged periods of high soil moisture. The increased
incidence of Sclerotinia watery rot during the past few seasons is attributed to:
(i) freezes and cold temperatures followed by long periods of soil moisture near
capacity which have stimulated apothecia and spore production; (ii) increased
acreage of A&C No. 5 Plus and Savoy; and (iii) in the Bunnell area, increased
use of overhead irrigation which has maintained favorable conditions for continued
production of air-borne spores.
SUGGESTIONS FOR CONTROL OF SCLEROTINIA WATERY ROT
The most effective means of control center on using sound management
1. When irrigating, particularly when using overhead systems, allow the surface
of the soil to dry between irrigation periods.
2. Avoid any condition which increases moisture on the plant surface e.g. plant-
ing in shaded areas; profuse weed growth; and heavy, frequent irrigations
which increase formation of guttation fluid at night.
3. Avoid injuring plants when cultivating or spraying.
4. If the disease occurs, chop cabbage as soon as practicable and thoroughly
disk it into the soil to hasten decay of the host tissue.
5. Flooding heavily infected fields for several weeks can reduce numbers of
sclerotia in the soil.
6. Crop rotation with poor hosts such as corn may be of some benefit.
RESTING BODIES(SCLEROTIA) ARE
* FORMED AMONG WHITE COTTONY GROWTH
ON CABBAGE HEADS WITH WATERY ROT
I C T I
ASCOSPORES INFECT WET INJURED OR
ASCOSPORES INFECT WET INJURED OR
DYING LEAVES AND INFECTION S
FROM THESE SITES
APOTHECIA PRODUCE THOUSANDS
W SCOSPORES WHICH ARE FOR-
CIBLY EJECTED INTO THE AIR
DISEASE CYCLE OF
SCLEROTINIA WATERY ROT
PREADS SCLEROTIA SURVIVE FROM SEASON
TO SEASON IN SOIL ;
ASCOSPORES BECOME AIRBORNE AND
SOME LAND ON WET CABBAGE FOLIAGE
MUSHROOMS(APOTHECIA) FORM ON
SCLEROTIA WHEN A PROLONGED WET
PERIOD(1O DAYS OR MORE) FOLLOWS
A PERIOD OF FREEZING TEMPERATURES