Diseases of Peppers

S. P. Doolittle.

Peppers are subject to diseases that cause wilts, leaf spots, fruit rots, and mottling, yellowing, and malformation of the leaves. Some of the most serious ones are caused by the agencies that produce diseases in tomatoes.

Wilt diseases due to the bacteria or fungi are common on peppers and often cause serious losses. They are of a type characterized by a decay of the stem at the ground line and a rather rapid wilting of the plant. These diseases are most common in the southern and southwestern United States.

Southern blight is serious on peppers in the Southeastern and Gulf States. It is caused by a fungus, Sclerotium rolfsii, which attacks many vegetables and other crops.

The fungus attacks the stem of the pepper plant at the soil line and causes a soft decay of the outer tissues. This girdling of the stem causes a wilting and yellowing of the leaves and an eventual drying of the stem and branches. The stems of diseased plants become covered with a white growth of the fungus in which are light-brown bodies (sclerotic) about the size of a mustard seed. When dead plants are pulled, a clump of fungus-infested soil often stays attached to the roots.

The fungus lives for a long time in the soil and requires warm, moist weather for its active development. It seems to be -most active in poorly drained, light, sandy soils. The sclerotic can live in the soil for some time and are spread by cultivation or washing rains. Under favorable conditions the bodies can put out fungus threads and infest new areas in the field.

Upper left: Pepper ring spot disease, caused by a strain of the cucumber mosaic virus. Upper right: Leaf stalks of celery infected with the brown spot fungus. Lower left: White rust of spinach, caused by a fungus. The disease is frequently widespread in Texas. Lower right: Peanut leaf spot disease on runner peanut leaves.

Bacterial wilt, caused by Pseudomonas solanacearum, affects peppers, tomatoes, potatoes, eggplants, and a number of other cultivated and wild plants. Like southern blight, it is most common in the warmer sections of the United States.

The first symptoms consist of a drooping of the leaves that is soon followed by wilting and death of the plant. When the stem of a wilted plant is cut across near the soil, the inner tissues have a dark water-soaked appearance. If the stem is pressed, there is a gray, slimy exudate from the vascular elements.

The bacterium causing this disease lives in the soil and infects the plant through the roots or stem. The organism usually is most destructive in low, moist, sandy soil and is most active at temperatures above 75 F.

Phytophthora blight of peppers occasionally occurs in the Southern States in moist, warm weather. The disease is caused by a fungus, Phytophthora capsici, which attacks stems, leaves, and fruits. The fungus infests the soil and may be carried on the seed.

The stem usually is infected near the soil and shows a dark, water-soaked band that may girdle the stein. Plants so affected soon wilt and die. Similar infection may occur higher up on the stem and single branches may be girdled and wither. Infected leaves show dark spots of irregular shape and size. They become dry and look as though scalded and bleached by the sun. On the fruits are dull, water-soaked patches, which soon cover the entire surface. The fruits shrivel and may remain attached to the plant.

Chili peppers in the Southwest are damaged by a wilt caused by the fungus Fusarium annuum. This fungus attacks the roots and the stem just below or at the soil line. Infected plants wilt and die rather rapidly from the injury to the stem.

The fungus lives in the soil but does seem to be carried on the seed. It is spread by irrigation water and on wind-blown particles of soil. The disease is most severe on heavy, poorly drained soils.

PEPPERS SUFFER from leaf diseases characterized by spots or large areas in which the leaf tissues are killed. To blame are fungi or bacteria, some of which also cause spotting or rot of the fruits. The most common are bacterial spot, caused by a bacterium, Xanthomonas vesicatoria (which also affects tomatoes) and cercospora leaf spot, caused by the fungus Cercospora capsici. Bacterial spot affects leaves and fruit. Cercospora spot attacks leaves and stems.

Bacterial spot causes severe injury to sweet peppers but is not serious on hot peppers. When infection occurs on young leaves of pepper, the spots are small, yellow green, and slightly raised on the under side. On older leaves the spots are not noticeably raised. If there are only a few, they may be one-fourth inch across and have a pale-tan center with a dark margin. If there are many, they remain small and dark in color. Severely spotted leaves turn yellow and drop. Infected seedlings may lose nearly all their leaves. Plants in the field often lose much of their older foliage. Some spotting of the stem occasionally occurs. The bacterium is carried on the seed and apparently lives over winter on the remains of diseased plants in the soil. Contaminated seed appears to be the chief source of initial infection. Infected seedlings are a source of further infection in the field. Severe outbreaks often follow long periods of warm, rainy weather, particularly when driving rain and wind cause slight injuries to the plants.

Cercospora leaf spot is sometimes known as frogeye spot, because the Spots on the leaves and stems have pale ray centers with a wide and darker pale-gray margin. They are oblong or circular and may be one-half inch in diameter. Severely spotted leaves generally wither and drop. A spotting of the leaf petioles also is a factor in the defoliation of the plants. The loss of leaves often is so great as to cause serious reduction in both size and quality of the crop. Hot and sweet peppers seem to be affected with equal severity.

The fungus causing cercospora leaf spot does not live very long in the soil but is carried on the seed. Field infection commonly can be traced to seedlings grown from contaminated seed. Spores of the fungus are produced in the tissues of the spots. Their spread is favored by the same conditions that favor the dissemination of the organism that causes bacterial spot.

PEPPERS ARE SUBJECT to a number of fruit rots. The most prevalent is the one that is known as anthracnose. It is caused by a fungus (Gloeosporium piperatum), which produces dark, sunken spots up to an inch across on sweet peppers. The spots occur on green or ripe fruits and eventually are covered with dark, raised specks the bodies in which spores are produced. The surface of the spots may be covered in moist weather with a salmon-pink mass of spores. A similar spotting of the fruit is caused by another fungus (Colletotrichum nigrum), which can attack the fruit only through wounds or injuries such as those caused by blossom-end rot. The symptoms it causes can easily be confused with those caused by G. piperatum.