Greenhouse-grown sweet bell pepper (Capsicum annum) plants are susceptible to attack by a number of insect and mite pests, including aphids, broad mites, greenhouse whiteflies, twospotted spider mites and western flower thrips. Insect and mite pests not only cause direct damage by feeding on the aboveground portions (e.g. leaves and flowers) of pepper parts, but can also cause indirect damage by vectoring diseases (e.g. viruses). Both types of damage may reduce plant growth and yields. Below are descriptions of each of these insect and mite pests, as well as plant protection strategies that can be implemented to alleviate problems with pests of greenhouse-grown peppers.
Insect and mite pests
Aphids are soft-bodied insects with tubes or tail-pipes (cornicles) protruding from the end of the body (abdomen). Aphids may vary in color from green, black, yellow, to pink. In greenhouses, all aphids are females (there are no eggs), with each individual female giving birth to approximately 100 live female nymphs, which can also give birth to their own live offspring. The rapid reproductive rate of aphids may result in extensive population outbreaks within a short period of time. Aphids can develop and reproduce throughout the year in greenhouses under continuous pepper production.
Aphid species that feed on greenhouse-grown peppers include the green peach aphid (Myzus persicae) and potato aphid (Macrosiphum euphorbiae). Green peach aphids are 1.2 to 2.5 mm long while potato aphids are 1.7 to 3.6 mm in length. Aphids feed on new terminal growth and the underside of leaves, causing both direct and indirect damage to greenhouse-grown peppers. Aphids cause direct damage by removing plant fluids with their piercing-sucking mouthparts; they feed on new growth that may cause leaf yellowing and plant stunting. Leaves affected may appear distorted or curled upward or downward. Excessive aphid populations may result in the presence of white cast or molting skins. The indirect damage caused by aphids is associated with the excretion of honeydew during feeding. Honeydew is a clear, sticky liquid that serves as a growing medium for certain black sooty mold, which may inhibit the ability of pepper plants to produce food by means of photosynthesis. Aphids may also vector certain viruses like Cucumber mosaic virus.
Broad mite (Polyphagotarsonemus latus) has four life stages: egg, larva, nymph and adult. Adult females are 0.2 mm in length, oval-shaped, and light-yellow to amber or green. An individual female can lay between 30 and 76 eggs on leaf undersides or in the depressions of small fruit. Nymphs and adults feed on the undersides of young leaves and flower buds, flowers and fruit. Broad mites inject a toxin into pepper plants that causes twisted, hardened, distorted and/or stunted terminal growth. Leaves may curl downward and turn purple in color. Fruit may be scarred and discolored, with premature fruit drop occurring under severe broad mite infestations. In addition, damaged fruit may be not be marketable.
Greenhouse whitefly (Trialeurodes vaporariorum) life stages include the egg, nymph, pupa and adult, which are located on the underside of pepper leaves. Adults are winged and about 4.5 mm in length, with the body covered by a white, powdery wax. Adults hold their wings flat, parallel to the top of the body. A female greenhouse whitefly adult can lay up to 20 eggs in small circles on the underside of leaves and may lay up to 300 eggs during their 30- to 45-day lifespan. Eggs are erect, spindle-shaped and attached to a short stalk. The eggs eventually turn gray and hatch in about four days into nymphs that move short distances on plants. Then they locate to a suitable place to settle down and start feeding. The pupa or fourth instar nymph does not feed and has distinct red eyes. Pupae possess elongated waxy filaments that encircle the body. The pupae are elevated in profile with vertical (perpendicular) sides. Development, from egg to adult, takes 14 to 30 days to complete; although development is contingent on the ambient air temperature, with warmer temperatures shortening the development time.
Greenhouse whitefly nymphs and adults have piercing-sucking mouthparts that are used to withdraw plant fluids. In general, nymphs cause greater plant damage because they feed more than adults. Direct feeding damage to peppers may result in leaf curling, leaf yellowing, chlorotic mottling, stunting and wilting. Greenhouse whitefly can also cause indirect damage by secreting copious amounts of honeydew.
Twospotted spider mite
Twospotted spider mite (Tetranychus urticae) adults are 0.3 to 0.4 mm long, oval-shaped, and yellow-green to red-orange. Adults have black markings on both sides of the body. Female adults live about 30 days, laying between 100 and 200 small, circular-shaped eggs during a two-week period. The eggs are deposited on the leaf underside along the mid-veins. Eggs hatch into yellow-green, six-legged larvae that transition into eight-legged nymphs and then develop into adults. Development, from egg to adult, can be completed in one to three weeks. Although, development is dependent on ambient air temperature. For instance, the life cycle takes 14 days at 21ºC (70ºF) and seven days at 29ºC (84ºF) to complete. All life stages are located on the leaf underside because twospotted spider mites are very sensitive to drying-up when exposed to ultraviolet light (sunlight).
Twospotted spider mites have piercing-sucking mouthparts that are used to feed on individual plant cells. Twospotted spider mite feeding reduces the chlorophyll content in leaves and decreases the ability of plants to manufacture food through the process of photosynthesis. Damaged leaves appear bleached and stippled with small, silver-gray to yellow speckles. Fine mottling on the upper leaf surface may be noticeable. Heavily infested leaves may appear bronzed, turn brown and eventually fall off pepper plants. In addition, webbing may be present on leaf undersides.
Western flower thrips
Western flower thrips (Frankliniella occidentalis) adults are approximately 2 mm in length, slender, with two pairs of “hairy” wings. The larvae and adults are brown-to-yellow. The life cycle consists of an egg, two larval stages, two pupal stages and an adult. The life cycle takes two to three weeks to complete depending on ambient air temperature, with the optimum range between 26 and 29ºC (79 and 84ºF). At these optimal temperatures, the life cycle can be completed in seven to 13 days. Adult females live about 45 days and can lay up to 300 eggs. The eggs are inserted into plant leaves during their lifetime.
Western flower thrips cause direct damage by feeding on pepper leaves and even flowers. Western flower thrips have piercing-sucking mouthparts that are used to feed within plant leaves. After inserting their mouthparts, western flower thrips lacerate and damage cell tissues, and then ingest fluids from the cells. Symptoms of feeding include leaf scarring, distorted growth and sunken tissues on leaf undersides. Black fecal deposits may also be present on the underside of pepper leaves. Western flower thrips cause indirect damage by vectoring the tospovirus Tomato spotted wilt virus. Plants infected with a virus must be disposed of immediately. The direct and indirect damage caused by western flower thrips may result in an economic loss to greenhouse producers.
One way of alleviating problems with insect and mite pests of greenhouse-grown peppers is to avoid over-fertilizing plants with high nitrogen-based, water-soluble fertilizers, as this may lead to the production of soft, succulent growth that is easier for insect and mite pests to penetrate with their mouthparts. Weeds inside the greenhouse should be removed immediately and deposited into containers with tight-sealing lids or placed into debris piles located away from the greenhouse. Many weeds serve as refuge sites for insect and mite pests and reservoirs for the viruses vectored by certain insect pests. A random sample of pepper plants should be monitored regularly for the presence of pests in order to detect localized infestations early in the production cycle.
Contact pesticides (in this case, insecticides and miticides) labeled for use on greenhouse-grown peppers should be applied early to prevent pest populations from building up to damaging levels. Thorough coverage of all plant parts, especially leaf undersides, is important in order to obtain greater kill of pests. Furthermore, multiple applications will be required due to the short residual activity of most insecticides/miticides and because of the dispersal and reproductive capacity of pests within greenhouses. In addition, environmental conditions such as temperature, relative humidity and light intensity that are favorable for growing peppers may promote the growth, development and reproduction of insect and mite pests. Heavily infested pepper plants should be discarded immediately. Consult with your local horticulture agent, state or university-based entomologist, and/or extension publications to determine those pesticides that are labeled for use on greenhouse-grown peppers.
Biological control or releasing natural enemies such as parasitoids and/or predators is another option for dealing with these pests. There are a number of commercially available parasitoids and predators that can be introduced to regulate pest populations on pepper plants. However, natural enemies must be released before pest populations are extensive and causing damage. Contact your local supplier/distributor to determine natural enemy availability for specific insect and mite pests.