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Bacterial Leaf Spot (bacterium - Xanthomonas campestris pv. vesicatoria):
Small, yellowish-green spots develop on the leaves [Picture].
The spots become brown and under favorable weather conditions, they become
numerous, enlarge, and coalesce [
Picture]. This leads to defoliation [Picture].
The pathogen can also cause wart-like, dark brown spots on the fruit [Picture]
or on the peduncle [Picture].
Damage
caused by leafminer may be mistaken for bacterial leaf spot [Picture].
The pathogen is seedborne, but can also persist in crop residue. Splashing
rain or overhead irrigation can spread the pathogen within the field. The
disease is controlled by using clean seed and crop rotation. A copper spray
program initiated on a preventative basis early in the growing season will
reduce disease development.
Black
Spot
(unknown, possibly physiological): There are black circular or irregular-shaped
spots on mature fruit that are beneath the epidermis and are not raised
[Picture]. The discoloration
extends to the interior of the fruit [Picture].
No pathogens have been found in association with this disease and factors
required for its development are not known. The disease occurs occassionally
in Texas.
Damping-Off
(fungi - Rhizoctonia solani, Pythium sp.): Small, emerging seedlings wilt
and die soon after emergence. Root systems of surviving plants are damaged,
resulting in stunted plants and poor yield. Use fungicide-treated, high-quality
seed and plant on a well-drained bed.
Herbicide
Injury:
Trifluralin (Treflan) injury can cause swelling of the stem near the soil
line [Picture].
Leaf
Spot
(fungus - Cercospora capsici): This disease rarely occurs in Texas. Spots
on leaves are circular with light gray centers [Picture].
Spots may also be present on the stem. Severe leaf infection lead to yellowing
and defoliation. The fungus is seedborne and can survive on crop residue.
Phytophthora
Blight
(fungus - Phytophthora capsici): The lower stem adjacent to the soil becomes
brown [Picture]. However, a
direct application of nitrogen fertilizer to the stems of transplants may
cause similar symptoms [Picture].
The rotting of the stem results in wilting [Picture].
However, flooding of the roots for long periods of time can also cause wilting
[Picture]. 
The
fungus is soilborne, but splashing water can spread the fungus to above-ground
portions of the plant, including fruit. Planting on a raised bed and avoiding
excessive moisture through proper irrigation management will reduce the disease.
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Powdery
Mildew
(fungus - Leveillula taurica): Yellow areas that may become brown occur
on the upper leaf surface [Picture].
A white, powdery growth occurs on the underside of the leaf [Picture].
Heavy infection may result in defoliation. The disease is favored by warm,
humid conditions. It is not a common or significant disease in Texas.
(fungus - Sclerotium rolfsii): The fungus attacks the stem of the plant near the soil line, causing the plant to wilt and die. A white, cottony growth is seen on the surface of the stem, along with tan or brown spherical bodies the size of mustard seed. Crop rotation and deep plowing of crop residue can be used to reduce disease development in future plantings. This disease is not common in Texas.
See section on Southern Blight
Sunscald
(physiological): Portions of the fruit have a dried, bleached appearance
and are sunken [Picture].
The tissue is often colonized by saprophytic fungi, which give it a black,
velvety appearance [Picture]
and lead to the wrong conclusion that a fungus is the cause of the problem.
This disease occurs as a result of exposure of fruit to direct sunlight
and can be a consequence of the defoliation caused by leaf-infecting pathogens.
Virus
Diseases: Many viruses infect peppers. Sometimes, plants are infected by a combination of viruses. This, and the variation in symptoms produced as a result of cultivar and environmental differences, make identification of virus diseases by symptoms alone unreliable. A typical virus symptom is leaf mosaic, which is a mottled, non-uniform appearance of color. The pepper mottle virus, which is spread by aphids, causes such mottling [Picture]. Another virus, the Texas pepper geminivirus, which is spread by whiteflies, causes a yellowed, mottled appearance [Picture], in addition to leaf curling and distortion. Viruses can cause stunting; for example, the pepper mottle virus [Picture]. Some of the symptoms caused by the cucumber mosaic virus, which is transmitted by aphids, include vascular and fruit discoloration [Picture] or death of terminal portions [Picture]. The tobacco etch virus, which is transmitted by aphids, can cause mosaic, fruit distortion and stunting, but in the cultivar 'Tabasco', it can cause a lethal wilt [Picture ].
Pepper-infecting
viruses can infect other species of plants, often without producing symptoms.
These viruses can be transmitted from such plants to peppers by feeding activities
of insects such as aphids, whiteflies and leafhoppers. However, vector control
is not usually a good strategy for virus control. By the time the vector is
noticed on the pepper, the plants are already infected. Once a plant is infected
with a virus, the infection can not be cured. If the infection occurs early
in the life of the plant, there may be severe yield loss. In areas where pepper
viruses and their vectors are endemic, the use of transplants or row covers
can protect the plant during the early, critical growing period. Sometimes,
cultivars resistant to a particular virus are available. Weed control both
within and around a field may help by reducing the available virus reservoirs.
Virus
disease diagnosis can be difficult and can require the use of a plant disease
diagnostic laboratory. To complicate diagnosis, sometimes agents other than
viruses can cause virus-like symptoms. For example, a chimera can cause mosaic-type
symptoms on leaves [Picture].
A chimera is a genetic mutation, which occurs rarely, i.e. one plant in a
field. Persistent high temperatures (exceeding 100 F) at planting time can
injure young seedlings, resulting in distorted foliage [Picture].
Broad mite injury can cause slight [Picture]
or severe leaf distortion [Picture
].
See section on Virus Diseases
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