Insects affecting solanaceous crops
Authors: Dr. Alton “Stormy” Sparks, Jr. and Dr. David G. Riley - University of Georgia
The term "solanaceous crops" generally refers to plants in the nightshade family, Solanaceae, within the Genera Capsicum (peppers), Lycopersicon (tomato), and Solanum (eggplant and potato). When referring to fruiting vegetables, all of the above except potato, a root/tuber crop, are included. However, many of the insects that attack tomato also attack potato. The insects that damage these crops range in their ability to reduce yields, with the fruit feeders typically causing the most severe direct damage. However, insects that transmit disease agents, such as whitefly or thrips vectored plant viruses, can also have similar devastating effects on yield. Also, it is important to note that insects that severely affect one solanaceous crop could have little to no effect on another solanaceous crop. For example, broad mite can produce severe symptoms in pepper, but have been rarely reported in commercial tomato fields in the southeastern USA.
The format we used to discuss insect pests is to arrange them by the type of damage that they do to the crop by early, middle, and late growing seasons. Pest descriptions are included in the following sections and the levels of injury expected from an insect species are noted by crop species. For specific commercial control options, please refer to the tomato, pepper, and eggplant sections of the UGA Pest Management Handbook. Additional outside information can be obtained from the University of California's "UC IPM Guidelines for Tomato" and John Capinera's "Handbook of Vegetable Pests" from Academic Press.
Insects Attacking Solanaceous Crop Seedlings (Early Season)
In Georgia, tomato, pepper, and eggplant are typically transplanted from greenhouse plant production sites on the same farm or from commercial plant producers. Since all of these crops are susceptible to frost damage, early planting in greenhouses followed by transplanting into the field avoids freeze damage. This is particularly important for tomato in the spring when early planting takes advantage of early favorable market windows. It also can avoid early season pests. Additionally, greenhouse or shade house transplant production concentrates expensive chemical treatments into a much smaller area and guarantees more uniform plant stands in the field. Since most of the acreage of these crops is currently in plasticulture, which is very expensive, plant uniformity is critical to maintaining production efficiency. However, these types of high input, uniform production practices also can lead to specific insect problems that can be exacerbated in these controlled environments. For example, insecticide treatment in greenhouses can concentrate selection for pesticide resistance to that insecticide if resistant insects survive the greenhouse production and are carried with transplants to the field. Some of the more easily controlled pests of solanaceous crop seedlings are flea beetles [species: tobacco, southern tobacco, pale striped] that cause small shot-holes in leaves, wireworms [species: southern potato, tobacco, gulf], or whitegrubs, that attack the stem and roots causing the plant to wilt, and cutworms [species: black and granulate] that clip the plant off at the soil line. The treatment timing for soil insects, such as wireworms, is usually at bed formation using soil fumigants. For later invading cutworms, it is at the time that damage is first detected, and for defoliators, it is at 10% defoliation. Currently, the most difficult early season pest to control is thrips [species: tobacco, westernflower] that transmit tomato spotted wilt virus (TSWV) which causes a severe wilt disease in most solanaceous crops. Tobacco thrips usually settles on tomato very early in the season beginning at transplant. Control options for this include host plant cultivars resistant to the virus, metallic reflective mulch (shown to be effective in tomato), early season insecticides targeting thrips and reducing thrips feeding at transplant, and plant activators that chemically induce resistance. Pre-season weed monitoring for thrips and TSWV can help to predict risk at a given location.
Insects Attacking Solanaceous Crops During Vegetative Growth and Flowering (Mid-Season)
Probably the most severe insect problem in early spring in the coastal plain of Georgia is thrips that transmit TSWV. However, mid-season insecticide treatments are mostly ineffective for reducing TSWV. Early season, preventative treatments are much more effective. In the early spring, usually no Lepidoptera pests attack tomato and pepper, but can occur at the end of the spring season. Where it occurs, pepper weevil can be the most severe pest in peppers (it does not damage tomato), but the distribution in Georgia is mostly limited to farm sites where weevils were introduced and populations were not systematically eradicated. Pepper weevil must be controlled by flowering to prevent establishment of damaging levels in the field. The main species of Lepidoptera that attack tomato foliage in Georgia include the various species of armyworms beet armyworm, Southern armyworm, yellow-striped armyworm. Other Lepidoptera pests include cabbage looper, tobacco hornworm, and tomato fruitworm. Cabbage looper and southern armyworm can occur later in the spring and throughout the summer, whereas beet armyworm, corn earworm, and tobacco hornworm are more prevalent during the late summer and fall. Other important chewing insects that can occasionally occur on tomato and eggplant are Colorado potato beetle and vegetable weevil.
Another group of insects that can reduce the quality of foliage during mid-season in the spring is aphids [species: potato and green peach] which secrete honeydew thus promoting the presence of sooty mold on leaves. During early to mid-season in the late summer and fall, sweetpotato whitefly can transmit geminiviruses that severely stunt plant growth and affect fruit quality. Whiteflies also can produce a honeydew that results in sooty mold when adult and nymph numbers are high. Two other foliage feeders that have been reported in Georgia in recent years are mites spider mites in tomato and eggplant and broad mite in pepper and eggplant] and less frequently, leafminers. Broad mite occur more frequently in the fall production season, but spider mites can occur in the spring and fall growing seasons. Insects that should be controlled mid season to avoid bloom drop and damage to fruit buds include stink bugs [species: southern, brown and green], leaffooted bugs, and other plant bugs. Thresholds for initiating control actions against insect pests in Georgia closely follow those recommended by University of Florida IFAS and include the one Lepidoptera larva or bug per six plants threshold prior to fruit formation. Thrips populations greater than 5 per blossom can cause direct damage, but again, most of the damage occurs at much lower levels when thrips vector TSWV, and this must be prevented at an earlier plant growth stage. Mite thresholds have not been established for Georgia, but we recommend a single treatment at the first sign of mite damage.
Insects Attacking Mature Solanaceous Crops (Late Season fruit feeders)
Insect control becomes critical once developing fruit are present. Most of the Lepidoptera pests previously mentioned can damage the fruit either by surface feeding or boring directly into fruit. In Georgia, tomato fruitworm and beet armyworm are both typical summer pests that bore into tomato fruit. Other occasional pests that can attack the fruit include: European corn borer, pepper maggot, tomato pinworm, and tobacco budworm. Worms that feed on fruit surfaces after extensive foliar damage late in the season include tobacco hornworm and various armyworms. The treatment threshold for worms that attack the fruit is very low. Depending on the amount of scouting done, the presence of worms in the field usually signals the need for treatment. Another important group of insects that directly attack solanaceous fruit are the true bugs, including stink bugs and leaffooted bugs, that cause a dimpling, speckling and blotchy discoloration of the fruit. This type of damage often does not become apparent until the fruit begins to ripen (for example, the pink and red stages of tomato ripening). Other insects that cause dimpling of tomato are thrips. Insects that cause irregular ripening of tomato include whiteflies. This can be directly from whitefly feeding or indirectly through the transmission of geminiviruses. Thrips vectored tomato spotted wilt virus also causes distinctive irregular ripening with circular patterns on the fruit. In pepper, dimpling of the fruit can be a sign of pepper weevil oviposition into the fruit. This can occur on fruit that appear marketable to the untrained eye, thus allowing infested fruit to be processed and shipped. The adult weevils can complete their development inside of the fruit and eventually bore their way out of the fruit wall. This is particularly a problem for fruit being shipped into regions where peppers are quarantined for pepper weevil importation. Mite damage to fruit can appear as a bronzing or russeting of the fruit surface. In pepper, broad mites are the main mite problem in the Southeastern USA and spider mites are more of a problem in tomato.