Alan
McNab
Professor of Plant Pathology |
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Bacterial Spot, caused
by the bacterium Xanthomanas cesicatoria, affects leaves and
fruit of pepper and tomatoes. Leaf spots appear first on lower
surfaces of leaves as small irregular water-soaked sreas. Spots
enlarge up to 1/4 inch in diameter, become purplish gray with
black centers, and may have narrow yellow halos. Spots on upper
surfaces of leaves are depressed; those on the lower surfaces
are raised. Spotted leaves may become ragged. Uneven marginal
leaf growth may cause twisting, and many leaves turn yellow and
drop off, thus exposing fruit to direct sunlight which may cause
sunscald. Fruit spots caused by the bacteria begin as water-soaked
areas and then become raised and scablike. The causal bacterium
is seed-borne. Seed and infected transplants are the principal
source of initial inoculum. The bacteria can survive for about
a year in residue from diseased plants. Bacteria are spread from
plant to plant by splashing water and by implements and workers
in fields when foliage is wet. Disease development is promoted
by moist conditions. |
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Cercospora Leaf Spot,
caused by the fungus Cercospora capsici, is characterized
by large circular or oblong spots on leaves and stems. Usually,
spots have light-gray centers with dark brown margins and may
be up to 1/4 inch in diameter. Severely affected leaves turn
yellow and drop. The causal fungus is carried on seed and possibly
survives one season in residue from diseased plants. Disease
usually gets started in seedbeds. Disease development is promoted
by prolonged periods of warm wet conditions.
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Downy Mildew, is caused by Peronospora
tabicini, a fungus that primarily attacs tobacco but occasionally
affects pepper and eggplant in seedbeds. Affected seedlings may
die. The fungus overwinters in soil. Spores may spread from tobacco
seedbeds to pepper seedbeds. Moist cool conditions favor disease
development. |
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Southern Blight, caused by the fungus
Sclerotium rolfsii, affects many vegetables, including beans,
beets, cole crops, carrots, corn, cucubits, eggplants, lettuce,
onions, peas, peppers, potatoes, radishes, sweet potatoes, and
tomatoes. Affected pepper plants wilt suddenly, turn yellow and
finally brown. Sclerotium is a soil-borne fungus that attacks
the crown of the plant. Crown tissue and external root tissue
first becomes soft; fungus mold with tiny brown clerotia (fungus
reproductive and survival structures) then grows over the base
of the stem and nearby soil. The fungus overwinters as sclerotia
in soil. Southern blight is more important in southern areas
than in northern areas. |
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Phytophthora Blight, caused by the
fungus Phytophtora capsici, can affect all parts of the plant.
Damping-off can develop on seedlings. Symptoms on older plants
include root rot, stem canker, leaf blight, and fruit rot. Affected
areas may be bordered by a white mold growth. Disease most frequently
appears in the wettest areas of a field. Warm wet weather promotes
disease development. |
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Anthracnose, caused by the fungi
Colletotrichum piperaturm and C. Capsici is characterized by
circular sunken spots on green and ripe fruit. In moist conditions,
pinkish to yellowish masses of glue-like spores, sometimes accompanied
by tiny black bristles (setae), appear on the spots. The fungus
overwinters on and in pepper seed, and in residue from diseased
plants. Disease is promoted by wet conditions (heavy fog, dew,
drizzle) and relatively high temperatures (90 %deg F).
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Alternaria Rot is caused by a fungus,
Alternaria solani or Alternaria tenuis. The fungus is reported
to enter wounds (sunscald or punctures). Dusty black spores on
fruit spots are characteristic. |
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Bacterial Soft Rot, caused by the
bacteria Erwinia caratovora, causes a depression at the fruit
surface. Internal tissue rapidly becomes soft and watery. Soft
rot bacteria usually are prevalent wherever fruit are grown and
packaged; invasion usually is through a wound. |
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Blossom-End Rot, caused by insufficient
calcium when fruit are forming, develops at the blossom end of
fruit and may affect up to half a fruit. Affected areas are first
water-soaked but soon become dry, light colored, and papery.
Additional information is presented under blossom-end rot of
tomato. |
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Sunscald, caused by intense sunlight,
occurs on any part of the fruit exposed suddenly to direct sunlight.
Wind whipping and leaf blights often provide conditions favorable
for sunscald. Affected areas are first light-colored, soft and
slightly wrinkled; these areas later dry and become lightly sunken,
whitish and papery. Affected areas may become discolored when
miscellaneous fungi grown on them. |
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Viruses that may occur on peppers
include i) tobacco mosaic (TMV), ii) potato virus X (PVX), iii)
cucumber mosiac (CMV), iv) tobacco etch (TEV), v) potato virus
Y (PVY), and vi) alfalfa mosaic (AMV). Symptoms vary, depending
on the virus or strain, the plant, time of year, and environmental
conditions. The range of virus symptoms may include leaf mottling,
puckering, or curling; stem and petiole streaking; rough, deformed,
or spotted fruit; stunted plants; and blossom and fruit drop.
Cucumber Mosaic Virus
Tobacco Mosaic Virus
Potato Virus X
Tobacco Etch Virus
Potato Virus Y
Alfalfa Mosaic Virus
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