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Ft. Pierce ARC Research Report FTP-1983-2
PHYTOPHTHORA BLIGHT OF PEPPER INCITED BY PHYTOPHTHdRA-_ 6I L-~-
D. O. Chellemi and R. M. Sonoda
I --* 1 ^`
Phytophthora blight of pepper (Capsicum annum L.) incited by
Phytophthora capsici Leonian consists of two relatively distinct
phases, a foliar blight and a crown and root rot. The foliar blight
phase of the disease was first observed in the U.S. in New Mexico in
1918 (3). The second recording of the disease in the continental
United States was that of Weber (8) in 1930 who reported both phases
of the disease in Florida. Phytophthora blight has been a sporadic
disease with heavy losses reported in Florida in 1950 (7), 1953 (2),
and 1959 (6). In November, 1982, a severe epidemic of the foliar
blight phase of the disease occurred in vegetable crops along the
southeast coast of Florida. Symptoms were noted on the stems, leaves
and fruits of pepper, stems, fruits, growing points of eggplant
(Solanum melongena var esculentum), growing points and fruits of
squash (Cucurbita pepo var melopepo) and fruits of tomato (Lycopersicon
esculentum Mill.). The root and crown rot phase of the disease re-
sulted in continuous heavy losses of pepper throughout the winter
of 1982-83 on several farms. Losses to root and crown rot were also
substantial in eggplant. Environmental conditions during the 1982-
83 growing season marked by warm temperatures and record setting
rainfall in November, January, and February (1) were extremely favor-
able for the development of both phases of the disease.
Different pathogenic strains of P. capsici are known to exist
(4). Pathogenicity tests on eggplant, pumpkin, squash, tomato and
two varieties of bell pepper indicated that there were pathogenic
differences among P. capsici isolates collected from southeast Florida
farms during the 1982-83 growing season (Chellemi and Sonoda, un-
published). Both mating types of the fungus, required for sexual
reproduction, are present in Florida (Chellemi and Sonoda, unpublished).
Whether oospores, produced during sexual reproduction, serve as over-
summering structures of P. capsici in Florida is not known. Spread
of the fungus can occur as sporangia in wind-blown rain (5). The
fungus can be moved in infested soil: through irrigation, on farm
machinery, trucks, automobiles, etc.
Symptoms. Although the crown rot and foliar blight phases of
Phytophthora blight on pepper may be distinct, most P. capsici
isolates are capable of inciting both phases. In addition the fungus
is reported to cause damping-off of very young seedlings. Plants
can have both crown rot and foliar blight at the same time. Entire
young plants can become necrotic in a few days when affected by
both phases of the disease. In mature plants, infection of the
1Biologist and Plant Pathologist, University of Florida, Institute of
Food and Agricultural Sciences, Agricultural Research Center, Fort
Pierce, FL 33454
growing point results in a dark water-soaked lesion that can spread
down the stem. Growth of lesions on mature stems generally ceases
after a period of time. The line of demarcation between infected
tissue and healthy, tissue is usually distinct. Leaf infections are
irregular in shape and have a scalded appearance. Fruits of pepper,
squash, eggplant, and tomato can be invaded from the blossom end,
stem end or elsewhere on their surfaces. Lesions on fruit have a
dark water-soaked appearance. Stems infected by the crown rot phase
show a dark band near the soil line. The lesion slowly spreads up-
ward. During humid conditions a white fuzzy growth may be seen in
lesions, generally more commonly on crown or lower stem infections.
The pathogen can attack roots with a general wilt being the only
above ground symptom.
Control. No commercial pepper varieties resistant to P. capsici
are available. Sanitation and-manipulation of cultural practices are
important measures in controlling P. capsici. Vehicles should be
kept out of the fields during wet periods when standing water is
present to prevent splash dispersal of the pathogen from the roadways
to the beds. Peppers infected by splash inoculum can serve as sources
of inoculum for further .spread of the disease. .Thinned-seedlings
should not be discarded into the alleys as they may serve -as media -
for survival and development of the fungus. Fields should be kept:
free of pepper, .eggplant, squash, tomato or other volunteer host
plants as well as nightshade and other solanaceous weeds during
the summer. Avoid-planting in low wet fields as the disease is
favored in such areas. Avoid planting peppers in fields with a re-
cent history of P. capsici problems. Studies are needed to determine
if rotation with non-host crops will have a significant effect on
reducing inoculum of the fungus in Florida. Currently zineb and
copper sulfate are the only fungicides labeled for control of P.
capsici on pepper. -Adequate control with these products is difficult
Literature Cited -
1. Anonymous. 1982-83. Local Climatological Data. National Weather
Service, West Palm Beach.
2. Cox, R. S. 1954. Annual Report. Florida Agr. Exp. Sta. p. 239.
3. Leonian, L. H. 1922. Stem and fruit blight of-peppers -caused by
Phytophthora capsici sp. Nov. Phytopathology 12:401-408.
4. Polach, F. J. and R. K. Webster. 1971. Identification of strains
and inheritance of pathogenicity in Phytopthora capsici.
5. Schlub, R. L. 1983. Epidemiology of Phytophthora capsici on bell
pepper. J. Agric. Sci., Camb. 100:7-11.
6. Stall, R. E. 1960. Annual Report. Fla. Agr. Exp. Sta. p. 266.
7. Swank, G., Jr. 1951. Annual Report. Fla. Agr. Exp. Sta. p. 138.
8. Weber, G. F. 1932. Blight of peppers in Florida caused by
Phytophthora capsici. Phytopathology 22:775-780.