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Disorders, Pests & Diseases of Chiles
by Paul Bosland
Control of disease and pests is one of the most important factors in producing a bountiful crop of chiles. Many of the diseases and pests that attack chiles reduce the harvest and the quality of the fruit. Frequent examination of your chile plants will help identify potential threats. Correctly diagnosing the problem is essential so that you choose the proper treatment—and avoid unnecessary and expensive ones.
As a general rule, most pests cannot be eradicated, but they can be managed so that the risk of loss is minimized. The best way to manage pests is to take action before they become serious; after the problem is well established, it is usually difficult to control.
Disease and insect control must start before chile plants and seeds ever reach the garden. Choose disease-resistant chile cultivars (see box on resistant varieties). Rotate your chile crop to help minimize disease, especially root rot diseases caused by soil-borne pathogens. Space plants properly to provide adequate air movement and help reduce the severity of foliar diseases. In addition, planting healthy seeds and transplants, controlling water in the root zone, getting rid of insects that carry disease, and removing weeds will help you produce an abundant crop of high-quality chiles.
Sunscald affects large-pod green peppers. (Photo: Paul Bosland)
Both nonliving (abiotic) and living (biotic) agents can cause chile disease and injury. Nonliving factors include extremes of temperature, moisture, light, nutrients, soil, pH, air pollutants, and pesticides. Living pathogens that cause disease include bacteria, fungi, mycoplasmas, vi-ruses, insects, and nematodes.
Descriptions, symptoms, and least toxic controls of some of the major abiotic disorders, bacterial diseases, fungal diseases, viruses, and pests affecting chile peppers are listed below. Not all the diseases and pests occur in the same region or at the same time of year.
Abiotic Disorders
Some abiotic disorders are caused by the lack of a major nutrient such as nitrogen or potassium. Abiotic disorders can also result when certain elements—aluminum, boron, or copper, for example—are overly abundant. These disorders can be similar in appearance to biotic diseases, so carefully investigate the cause of the problem. You can control some of these disorders by avoiding extreme temperatures, inferior soils, and (if possible) air pollutants.
Blossom-end Rot
This disorder first appears as a water-soaked area on the fruit. The tissue near the blossom end of the pods has a brown discoloration. Blossom-end rot in chiles, unlike tomatoes, is never actually at the blossom end of ther fruits. Spots elongate and become brown to black, dry and leathery. Pods affected with blossom-end rot usually ripen prematurely. Wilting, lack of soil moisture, and lack of calcium encourage the problem.
To control blossom-end rot, maintain uniform soil moisture through irrigation and avoid large amounts of nitrogen fertilizer.
Herbicide Injury
Hormone-type herbicides such as 2,4-D, which is commonly found in lawn fertilizers, can cause distorted leaves. Other herbicides may cause chlorosis (yellow, brown, or black areas of dead tissue [necrosis]), or lesions.
Sunscald
Sunscald results when fruits that have been growing in the shade are exposed to too much sunlight. Smaller-podded varieties of chile with erect fruits are not as susceptible as large-podded varieties like bells and New Mexicans. Mature green fruits are more sensitive than mature red fruits. Symptoms include a whitish necrotic area on the side of the fruit exposed to a fierce, usually afternoon, sun.
Keep pods shaded by the plant's leaves or by screening. During harvest, remove as few leaves as possible and keep other damage to a minimum. Avoid stressing the plant.
Biotic Disorders
Plant pathogens and pests are among the most common causes of reduced yields in chiles. Chile diseases have common names such as root rot, foliar blight, and fruit rot, which typically describe the plant part that is affected; but the most useful criterion for describing a disease is the organism causing the problem.
Bacterial Diseases
Bacterial spot (Xanthomonas campestris pv. vesicatoria)
Bacterial spot may be the most serious bacterial disease affecting chiles. On young leaves, it causes small, yellowish green to dark brown, raised spots. On older leaves, the spots are dark, water soaked, and not noticeably raised. When spots are few, they may enlarge to 1/8 or 1/4 inch in diameter. The spots appear angular, as the bacteria spreads along the veins. These spots have dead, straw-colored centers with a dark margin. Severely spotted leaves turn yellow and drop. The organism is seed-borne and, in some areas, can overwinter on diseased plant debris. Infected seedlings carry the disease to the field, where it can spread rapidly during warm, rainy weather, especially when driving rain and wind have caused injuries to the plants.
Management of bacterial spot depends on a combination of practices. The most important of these are crop rotation, use of disease-free seed and seedlings, resistant cultivars, and good garden sanitation. Fixed copper compounds are commonly used to help manage the disease, although they are not highly effective under environmental conditions optimal for disease development or when the problem is severe.
Bacterial Soft Rot (Erwinia carotovora pv. carotovora)
Bacterial soft rot affects the fruit. The internal tissue softens, and the pod turns into a watery mass with a foul smell. The disease is most frequent when the weather is hot and humid.
Keep chiles cool, below 70°F. Because the disease can also be started by insect injury, control insect pests.
Bacterial Wilt (Pseudomonas solanacearum)
Bacterial wilt begins with a wilting of leaves. After a few days, a permanent wilt of the entire plant results, with no leaf yellowing. Test for this bacteria by cutting the roots and lower stems; look for milky streams of bacteria when they are suspended in water.
The best control is to plant clean seed and transplants.
Fungal Diseases
Fungi comprise one of the largest groups of organisms causing diseases among chiles. The most important fungal diseases in the home chile garden are discussed below.
Anthracnose (Colletotrichum species)
Anthracnose is the common name for the disease caused by several species of fungus in the genus Colletotrichum. The disease is most serious on ripe pods. Symptoms are small, water-soaked, shrunken lesions that expand rapidly. The lesions have dark fungal spores in them, and a characteristic concentric ring or target-shaped spot.
Clean seed and crop rotation are important in preventing anthracnose.
Early Blight (Alternaria solani)
Early blight causes damage to the leaves and the fruit. The disease appears as small, irregular, brown, dead spots, usually on older leaves. The spots, which are ridged and have a target pattern, enlarge until they are 1/16 to 1/4 inch in diameter. Early blight is usually more prevalent than anthracnose.
To protect against early blight, plant disease-free seed and seedlings.
Cercospora Leaf Spot (Cercospora capsici)
This disease is also called frogeye. Leaf or stem lesions are oblong or circular with a small, light gray center and dark brown margin, like a frog's eye. The diseased spots usually dry and fall from the leaf, leaving conspicuous holes. Leaf drop is common with severely infected leaves. Stems and fruits are especially susceptible to this disease, which is worst under humid conditions. The environmental conditions that favor this disease also favor bacterial spot. In fact, these two diseases, along with Alternaria, are often found together on infected leaves.
Because the disease is seed-borne, planting clean seed and crop rotation are important controls.
Damping-off/Seedling Disease
Several fungi, such as Pythium, Rhizoctonia, and Fusarium, are associated with this disorder. Seedlings fail to emerge (pre-emergence damping-off), small seedlings collapse (post-emergence damping-off), or seedlings are stunted (root rot and collar rot). Other causes of seedling loss include poor seed quality, improper planting depth, high salt concentrations, a wet seed bed, strong winds, severe nutrient deficiencies or toxicity, pre- and post-plant herbicide applications, and insects.
To prevent seedling diseases, plant only high-quality seed or vigorous transplants and avoid garden beds that are poorly drained.
Gray Mold (Botrytis cinerea)
This fungus causes a sudden collapse of succulent tissues, such as young leaves, stems, and flowers. Gray powdery spore masses occur on the surface of dead plant tissues. High humidity favors the disease.
To ward off gray mold, space plants widely so that they can dry quickly.
Phytophthora (Phytophthora capsici)
This water mold can invade all plant parts and cause at least three separate syndromes: foliar blight, fruit rot, and root rot. It spreads rapidly when humidity and temperatures are high and/or the soil is wet. The first symptom of root rot is severe wilting; within days the plant is dead.
Avoid excess water in the garden. Plant chiles on a high ridge to allow water to drain away from the roots.
Southern Blight (Sclerotium rolfsii)
Southern blight usually occurs during the hot and wet season. It causes plants to wilt as a result of stem girdling and rot at the soil surface—the base of the stem is brown and decayed above and below the soil line. White fungus is visible at the base of the stem and on the soil around the base. Sclerotia, small brown spheres about the size of mustard seeds, can be found in the fungus.
Cultivate shallowly to avoid scattering soil up on the plants, and remove infected plants promptly.
Verticillium Wilt (Verticillium dahliae)
The symptoms of verticillium wilt are highly variable. Plants may show a yellowing of leaves and a stunting. As the disease progresses, the plants can shed leaves and may finally die. If the stem is cut, a vascular discoloration is visible.
Crop rotation is the best control. No resistant cultivars are known.
White Mold (Sclerotinia sclerotiorum)
White mold, or sclerotinia disease, causes a wilt, rotting, or blighting of any above-ground or below-ground plant parts. At first, the affected area of the plant has a dark green, greasy, or water-soaked appearance. On stems, the lesion may be brown to gray in color. If the humidity is high, a white, fluffy mold growth appears. Lumpy areas appear in this white growth, which become hard and black as they mature. The hard, black bodies (sclerotia) form inside the stem or on the outside surfaces of the stem and other plant parts.
To guard against white mold, plant chiles in well-drained soil, rotate crops, and carefully remove all infected plants as soon as possible.
Viral Diseases
Some 45 viruses have been reported to infect chiles. Of these, more than half are transmitted by aphids. Viruses alter the plant's cells, causing plants to grow abnormally—leaves may be distorted, abnormally colored, mottled, or curled. Fruit can be mottled, spotted, or shriveled and plants stunted. Leaves, stems, flowers, and fruits may all be affected. One plant can be attacked by many viruses and express many different symptoms.
To protect against tobacco mosaic virus, avoid using tobacco in any form in the garden. Gardeners who use tobacco should wash their hands with soap and water or rubbing alcohol before handling plants. Early detection and removal of infected plants helps, but complete control is often difficult. It may be difficult to distinguish symptoms caused by mosaic diseases from those caused by abnormal soil pH, herbicide injury, nutritional deficiencies, and feeding damage by mites or insects.
To help reduce virus problems, plant virus-free seed, remove weeds, control insects, remove plants showing virus symptoms, and plant resistant varieties. The following practices have also been tried with varying degrees of success, particularly to prevent or reduce viruses transmitted by aphids: organic mulches; aluminum foil strips above the crop; insect traps; mulches of aluminum foil, silver vinyl, or white or translucent polyethylene; aluminum-painted polyethylene sheets; and mineral oil sprays. "Colored baits," sticky sheets of yellow polyethylene spread around the garden, trap the winged form of the aphids and are somewhat effective in controlling the spread of aphid-transmitted viruses. However, planting resistant cultivars is the best way to control viruses, and many virus-resistant cultivars are available. (See box on disease-resistant cultivars, page 55).
Insect Pests
The insect problems most common to chile plants are cutworms, aphids, pepper weevils, maggots, flea beetles, hornworms, and leafminers. To control the insect population and keep seedlings insect-free, inspect your plants daily, weed well around the chiles, dispose of diseased plants immediately, and, as a last resort, consider using pesticides.
Following are descriptions of the insects and other pests that most commonly attack chiles.
Cutworms
Early in the season, cutworms are the most damaging pests to both seeded and transplanted chiles. There are several species of cutworms; they are the larvae of a large family of moths. They are dull gray, brown, or black, and may be striped or spotted. They are stout, soft-bodied, smooth, and up to 2 inches long. When disturbed, they curl up tightly. Cutworms attack only seedlings. They cut off the stems above, at, or just below the soil surface.
Cultivation disturbs overwintering cutworms. To prevent cutworms from reaching young plants, place cardboard, plastic, or metal collars around the stems, pushing the collars 1 inch into the ground. Beneficial nematodes added to the soil in spring or fall will parasitize the larvae.
European Corn Borers (Ostrinia nubilalis)
Corn borer moths are a key pest because they can be found in most every garden every year. To control them, you must target the larval (caterpillar) stage. Moths deposit eggs on chiles, and as they hatch, the larvae tunnel into the chile pod.
Eggs hatch four to five days after being laid, and this is the most appropriate time for control measures. Spray plants with Bacillus thuringiensis (Bt), sold commercially as Dipel.
Flea beetles (Epitrix species)
Seeded chiles are subject to attack by flea beetles when the cotyledons (the first leaves to appear after seed germination) emerge. These black beetles are about 1/8 inch long. Young plants are severely damaged and full of holes.
Protect young plants with row covers. Give the plants a noontime shower; flea beetles feed at the height of the day, and they don't like to get wet.
Fruitworms
Fruitworms include the fall armyworm, beet armyworm, and tomato fruitworm (corn earworm). At the larval stage, the worms are green, brown, or pink, with light strips along the sides and back. They grow to 2 inches long. The fruitworm damages chile pods by eating holes in them.
Spray plants with Bacillus thuringiensis (Bt), sold commercially as Dipel.
Green Peach Aphids (Myzus persicae)
Green peach aphids can become numerous at any time, but are probably more prevalent during the summer. These aphids are usually light green and soft-bodied. They cluster on leaf undersides or on stems, and excrete a sticky liquid called honeydew, which creates spots on the foliage. A black fungus—sooty mold—may then grow on the honeydew and decrease photosynthesis. Severe infestations can cause wilting, stunting, curling, and leaf distortion.
Usually, aphid predators and parasites keep aphid numbers low, but the aphids can multiply quickly. Encourage and release ladybugs and green lacewings into the garden, because they are predators of aphids. An insecticidal soap spray can be used when numbers escalate.
Hornworms (Manduca sexta and M. quinquemaculata)
The worms are the larval stage of the sphinx moth; these large caterpillars have a green body with diagonal lines on the sides and a prominent horn on the rear end. They can be up to 4 inches long. They ravenously eat foliage and can strip a chile plant, killing it.
An easy control is to pick off the worms by hand. Alternatively, spray plants with Bacillus thuringiensis (Bt), sold commercially as Dipel.
Leaf Miners
Many species of flies will cause the leaf-mining disorder. The larva is yellow, about 1/16 inch long, and lives inside the leaves. The adult is a tiny black and yellow fly. Infected leaves are blotchy. The larvae make long, slender, winding "mines," or trails, under the epidermis of the leaves.
The best method of control for leaf miners is Bacillus thuringiensis (Bt), sold commercially as Dipel. If damage is minor, treatment is not necessary. Remove infested leaves.
Leafhoppers
Leafhoppers comprise an important group of little sapsucking insects. There are many species of leafhoppers, but the leafhopper Circulifer tenellus spreads curly top virus. These are usually green, wedge-shaped, up to 1/8 inch long, and fly quickly when disturbed. Leafhoppers can cause hopperburn, but it is rare in chiles. The tips and sides of chile leaves turn yellow to brown and become brittle.
Remove infested plants or plant parts immediately.
Pepper Maggots (Zonosemata electa)
The maggot is the larva of a tephritid fly. The slender white or yellowish white maggot is less than 1/8 inch long. Adults are yellow striped flies with dark bars on the wings. Maggots feed within the chile pod, causing it to decay or drop from the plant.
Pepper Weevils (Anthonomus eugenii)
The pepper weevil is a severe pest in tropical areas and can cause damage in temperate regions where it has been introduced. The adult feeds on leaves, blossom buds, and pods and will lay eggs on the flowers, buds, and fruit. The eggs hatch and the larvae, white with brown heads, burrow into the young pods, feeding inside the fruit. Premature fruit drop results.
Once the larvae are inside the fruit, practical control is impossible. Preventive measures include destruction of crop residue and weeds of the nightshade family (such as eggplants, tomatoes, and potatoes) to reduce the possibility of adult weevils overwintering. There are no known resistant cultivars at this time.
Thrips
There are many species of thrips and all are extremely small. They can produce a new generation every two weeks. Affected leaves are distorted and curl upward (boat-shaped). The lower surface of the leaves develops a silvery sheen that later turns bronze. The species Frankliniella tritici is the vector for tomato spotted wilt virus.
Sulfur and diatomaceous earth are effective against thrips.
Whiteflies
Whiteflies are minute insects with broad wings covered with a fine, white, waxy powder. The immature and adult stages suck plant juices from the leaves, causing them to shrivel, turn yellow, and drop. In addition, they can carry viruses to chile plants.
Whitefly control is difficult. Good cultural practices, such as removing infected plants, are the best controls.
Other Pests
Spider Mites (Tetranychus species)
Spider mites are red arachnids. When infestation is high, the leaves will have webs on them; if uncontrolled, these mites can kill a plant. Leaves curl downward, like an inverted spoon. Leaves or fruits become bronzed or russeted.
Insecticidal soaps provide some control.
Nematodes
Nematodes can be a serious problem in sandy soils. Symptoms, which vary with plant age and the severity of the infestation, include stunted, nonproductive plants and development of characteristic knots on the plant's roots. Above ground, the plant may be stunted and its leaves wilted. Roots infected with root-knot nematodes may have obvious swellings or galls, varying in size from smaller than a pinhead to larger than a pea.
The best control for nematodes is crop rotation; plant resistant cultivars when available (See box)
Paul Bosland is a professor of horticulture at New Mexico State University. He is one of the foremost chile pepper breeders in the world, and is coauthor of The Pepper Garden (Ten Speed Press, 1995) and Peppers of the World: An Identification Guide (Ten Speed Press, 1996).