Pepper Disease Control

Several diseases can reduce yields and quality of bell, pimento, and hot peppers. Control or prevention of these diseases is most important for profitable production of peppers.

Pepper diseases are classed as parasitic or nonparasitic. Most major diseases are caused by parasitic organisms (fungi, bacteria, nematodes, and viruses). Unfavorable soil or climatic conditions cause the so-called nonparasitic diseases, such as blossom-end rot and sunscald.

Bacterial Leaf Spot

Xanthomonas vesicatoria causes bacterial leaf spot on the leaves and fruit of pepper. The spots on young leaves are small, yellowish green, and slightly raised on the underside of the leaf. They often have an oily appearance. On older leaves, the spots are first dark, water-soaked, and not noticeably raised. These spots enlarge and have straw-colored centers with a dark margin. Severely spotted leaves turn yellow and drop.

On the fruit, small blister-like, irregular spots may be 1/4 inch in diameter. These spots later turn brown and develop a warty appearance.

The organism is seed borne and in some areas can overwinter on diseased-plant refuse in the soil. The main source of initial infections is infected seeds that carry the disease to the field where it spreads rapidly during warm, rainy weather.

Begin bacterial leaf spot control by using clean, treated seeds. If you use transplants, buy certified plants grown in disease-free soil. Bacterial leaf spot can be checked in the field by spraying with a copper fungicide (refer to table of recommended products) according to the manufacturer's label. See the "10-Point Control Program" at the end of this publication for details on seed treatment and spraying.

Cercospora Leaf Spot

Cercospora leaf spot is a common fungus disease found in many sections where pepper is grown. Cercospora leaf spot is characterized by large, circular, or oblong spots on the leaves and stems. These spots, which become dark brown at the margins and usually have light-gray centers, may be as much as 1/2 inch in diameter. Severely infected leaves turn yellow and drop. Stems of the fruit are especially susceptible to this fungus.

The fungus is seed borne. Field infections can usually be traced to infected seedlings grown from contaminated seeds. In the field, the fungus spores are spread mainly by wind.

Seed treatment and spraying with a fungicide control Cercospora leaf spot.

Southern Blight

Southern blight, caused by the fungus Sclerotium rolfsii, is a common and destructive disease of peppers in the Southeastern and Gulf States. This fungus attacks many other vegetables, field crops, and ornamentals.

During warm, rainy weather, the fungus attacks the stem of the pepper plant near the ground line and eventually girdles it. The diseased plant droops, the leaves wilt, and the plant finally dies. When an infected plant is pulled up, you can usually see a white mat of the fungus on the stem. In this mat there usually are embedded numerous small, light-brown bodies about the size of a cabbage seed. These bodies, known as sclerotia, are distinguishing characteristics of the disease.

The fungus infests the soil but makes little growth at temperatures below 70 degrees Fahrenheit. Threads of the fungus spread through the soil, and water or cultivation can distribute the sclerotial bodies. Under favorable conditions, these sclerotia put out fungus threads and infect the plant. The fungus lives a long time in the soil and is most active in sandy, poorly drained fields. Control includes crop rotation, deep plowing, and using PCNB in transplant water.

Mosaic

The virus that causes mosaic produces a distinct mottling and distortion of the leaves. Affected plants produce very few, poor quality pods.

Do not use tobacco when handling plants. Control weeds and insects around fields. Most varieties of bell pepper are resistant or tolerant to this disease.

Tomato Spotted Wilt Virus

Tomato spotted wilt virus (TSWV) is carried to peppers by several thrips species. Early infection causes stunted plants with mottled and distorted foliage. Frequently, ring spots appear on older leaves. Yields may be drastically reduced, and fruits produced are distorted and have black streaks. TSWV-resistant varieties are not yet available. A strict season-long, thrips-control program should be carried out, along with weed control in and around production fields. Higher plant populations may reduce TSWV severity by compensating for infected plants, but thicker plants may encourage buildup of foliar and fruit diseases. If thicker plantings are used, additional fungicide applications may be required.

Fruit Rots

Blossom-end rot is a common physiological disorder believed to be related to a calcium deficiency and a fluctuation in soil moisture. As the name implies, the injury always starts at or near the blossom end of the fruit. Peppers are most commonly affected when they are one-third to one-half grown, but the disease may occur at any stage of fruit development.

The first indication of any abnormality is a slight water-soaked area around the blossom end of the fruit. The area soon darkens and enlarges rapidly as the fruit begins to ripen. As the affected area increases in size, the discolored tissues shrink until they become flat or concave. The flesh is conspicuously decayed and brown to black and leathery.

Secondary fungi frequently invade the damaged tissue. The rot they cause may cause the grower to think a fungus is responsible for the damage.

To help reduce the incidence of blossom-end rot:

1. Supply adequate calcium through liming and fertilization.
2. Maintain a uniform supply of moisture to the plant.
3. Apply nitrate-nitrogen, in the form of calcium nitrate, as recommended by soil test results.

Sunscald of peppers occurs on parts of the fruit exposed to direct sunlight. The first evidence of the problem is a light-colored, soft, wrinkled area on the fruit. As the injured area dries, it becomes sunken and has a white, paper-like appearance. In many cases, secondary organisms enter through these areas.

Anthracnose, caused by a fungus, is one of the two most common rots found on pepper fruit. Diseased areas develop as dark, round, sunken spots that often reach an inch in diameter. Within these spots are small, raised specks (the fruiting bodies of the fungus). The disease is more severe during rainy weather because the spores are washed or splashed to other fruit.

The application of a recommended fungicide controls anthracnose.

Ripe Rot, caused by a fungus, is a serious problem on pimento pepper. Infection can occur any time after petal fall, but there is no sign of the disease until the fruit turns red.

The fungus can penetrate the seed cavity and infect the seed. As the fruit ripens, small light-colored spots begin to appear on the fruit, especially in damp weather. These are difficult to see before harvest. After harvest, the spots enlarge and become soft and sunken. When the diseased fruit is cut open, you will usually find a gray fungus growth around the seed pods.

The application of a recommended fungicide controls ripe rot.

Phytophthora and Pythium Rot are more prevalent during periods of warm, wet weather in wettest areas of fields. Affected areas of fruit are often covered with white mold growth. Additionally, these fungi can cause root rot, stem canker, and leaf blights. Planting time application of Ridomil 2E, followed by foliar sprays of Ridomil/Copper 70W, should be used as preventive treatments in fields where Phytophthora and Pythium fruit rots have caused problems.

Recommended fungicides for pepper disease control.

* Number in parenthesis following product is the time in days that should be allowed from last application until harvest.
Additional maneb and copper fungicides may be labeled for control of the pepper diseases listed.

10-Point Control Program for Pepper Diseases

1. Seed Treatment. Before seeds are planted, treat them with sodium hypochlorite at the rate of 1 pint per 4 pints of water. Wash for 40 minutes with continuous agitation; air dry and plant immediately. Prepare a fresh solution for each batch of seeds. This treatment is for bacterial leaf spot control. Just before the seeds are planted, treat them with Captan 50 WP for damping-off control. Do not use treated seeds for food or feed for animals.
2. Rotation. If at all possible, avoid planting pepper behind pepper, soybeans, or peanuts.
3. Deep Plowing. Turn land deeply to bury old crop residue that may contain disease-causing organisms, especially Southern blight.
4. Transplants. Most diseases attacking pepper can be brought into the field on transplants. Use disease-free transplants only. Buy only certified transplants that were grown from clean, treated seed on clean soil.
5. Transplant Water. For the control of Southern blight, use Terraclor (75 percent WP) in transplant water. Mix 3 to 5 pounds per 100 gallons of transplant water, and use 1/2 pint of solution per plant. This procedure does not totally prevent Southern blight, but reduces the incidence of the disease.
6. No Tobacco. Do not use tobacco of any kind while handling plants. Wash hands in soap and water before handling transplants. This reduces the chances of introducing a virus into the field. Use mosaic virus-resistant varieties when possible.
7. Spray. Refer to recommended fungicides table. These fungicides provide acceptable control of Cercospora leaf spot, anthracnose, ripe rot, and bacterial leaf spot. Apply at the first sign of spots on the foliage. Fungicides should be applied in enough water to obtain thorough coverage. If no leaf spot symptoms have been noticed by the time the first fruit turns pink, begin the spray program anyway -- even if no disease is present. Follow a 7- to 10-day spray schedule. If a severe disease outbreak occurs, apply the fungicides every 5 days. Copper fungicides do not completely control bacterial leaf spot, but help prevent disease spread. The excessive use of copper may retard plant growth.
8. Fertility. Plants perform better, produce more, and have fewer diseases when you follow the proper fertilization program. Higher rates of nitrogen and adequate phosphorus and potash reduce bacterial leaf spot. Highly fertilized plants grow well and set fruit before viruses and leaf spots become a problem. Using calcium-containing fertilizers aid in reducing blossom end rot in soils low in available calcium.
9. Destroy Weeds and Control Insects. Keep all weeds cut around the edge of pepper fields, and remove all weeds growing within the field. Many weeds carry viruses that can be transferred to pepper plants. Insects bring virus diseases into the field; therefore, insect control helps prevent the spread of viruses.
10. Destroy Virus-Infected Plants. As soon as you notice virus-infected plants, pull them up and burn them. If infected plants remain in the field, the virus can be spread to healthy plants. Infected plants have a bushy, distorted appearance.

Observe all directions, restrictions, and precautions on pesticide labels. It is dangerous, wasteful, and illegal to do otherwise.

Trade names are used for educational purposes only. The Mississippi State University Extension Service does not guarantee nor warrant the standard of any product mentioned; neither does it imply approval of any product to the exclusion of others that also may be suitable.

By Dr. Frank Killebrew, Extension Plant Pathologist

Mississippi State University does not discriminate on the basis of race, color, religion, national origin, sex, age, disability, or veteran status.

Publication 801
Extension Service of Mississippi State University, cooperating with U.S. Department of Agriculture. Published in furtherance of Acts of Congress, May 8 and June 30, 1914. RONALD A. BROWN, Director

Copyright by Mississippi State University. All rights reserved.

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