Tomato
Tomato: Caterpillars including tomato fruitworm, Helicoverpa zea (Boddie) (Photos 157 and 158), tobacco budworm, Heliothis virescens (Fabricius), and fall armyworm, Spodoptera frugiperda (Smith) (Photo 159), Lepidoptera: Noctuidae
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Photo 157 |
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Photo 158 |
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Photo 159 |
Biology: The majority of tomato produced in Arkansas is for early fresh markets and is produced in the south central area of the state. In this area tomato caterpillars generally occur in low numbers but the value of the crop often requires that the insects be managed. In other areas of Arkansas and especially in later planted tomato, damage may be severe and management is often required. Several caterpillars of the family Noctuidae attack solaneous crops including tomato. Behavior of each is similar. Adults emerge from pupae that are located within the first 10 cm of soil. Adults are large bodied moths and are covered in scales that often dislodge and give the appearance of being dusty. Shortly after emergence, moths mate and begin to lay eggs on tomato foliage and stems. Eggs of tomato fruitworm and tobacco budworm are laid individually while armyworm eggs may be laid in masses of up to 30. Eggs hatch within two to six days depending on temperature and emerging larvae feed on tomato foliage, blooms or fruit. The color and stripe pattern of larvae vary greatly and at maturity larvae may approach 50 mm in length. Multiple generations of caterpillars occur each season in Arkansas and generations overlap. Tomato caterpillars feed on numerous host plants both wild and cultivated.
Management: In the high value tomato production area of south central Arkansas, producers have a very low tolerance for any damaged fruit. Thus, insecticides are the mainstay of caterpillar management. Also, tomato plants in this area generally receive multiple applications of fungicides. The common practice is to tank-mix these with insecticides thus reducing application costs. In other areas of tomato production, alternative management may prove beneficial. Numerous beneficial organisms help to suppress the caterpillar populations including insect diseases, predatory and parasitic insects. Efforts at conserving these beneficials are important. To accomplish this, immediately after transplanting, tomato plants should be scouted for caterpillars. After transplanting, the use of “hard insecticides” should be delayed for as long as possible. Low numbers of tomato caterpillars may be tolerated with a minimal effect on yield. Removal and destruction of infested fruit will prevent the caterpillars from moving to adjacent fruit. Larger caterpillars on foliage can be removed by hand. If numbers of caterpillars increase beyond acceptable levels, use of “soft” insecticides such as BT may be warranted. Other “soft” insecticides include spinosad. If high levels of caterpillar populations persist despite use of “soft insecticides”, use of tradition insecticides may be warranted. Sanitation, including destruction of crops immediately following the last harvest, may have some effectiveness in reducing damage in subsequent plantings. Use of corn as a trap crop may also reduce the presence of fall armyworm and tomato fruitworm in tomato.
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Tomato: Tomato and tobacco hornworms, Manduca quinquemaculata (Hayworth) and M. sexta Linnaeus. Lepidoptera: Sphingidae
Biology: The tomato and tobacco hornworms are the largest caterpillars that occur on tomato in Arkansas. Numbers are generally low in commercial fields and management may not be required. In home gardens, however, feeding by the larvae may appear severe. Adult hornworm moths emerge from overwintering pupae from the soil in late spring. Tomato hornworm adults are large sphingid moths with 5 orangish markings along each side of the abdomen. Tobacco hornworm adults are similar but with 6 marks. After emerging, moths mate and begin to deposit eggs singly on the bottom of tomato leaves. Larvae hatch in 4 to 7 days and primarily feed on tomato foliage. Fruit may be consumed by larger larvae. Larvae feed for 3 to 4 weeks during which they can reach over 7.5 cm in length. Tomato hornworm larvae are green with 8 C-shaped white markings along each side of the abdomen. Tobacco hornworm larvae resemble tomato hornworm larvae but have only 7 diagonal lines along each side of the abdomen (Photo 160). Also, both larvae possess a distinct “horn” at the posterior of the abdomen. The tobacco hornworm horn is reddish and curved while that on the tomato hornworm is straighter and black. Damage from the larvae is easy to recognize and complete areas of the tomato plant can be consumed leaving only the tomato branch (Photo 161). When damage is observed, careful searching of nearby foliage can detect the larvae. Pupation occurs underground. A second generation usually occurs in Arkansas. Both hornworms occur throughout Arkansas.
Management: Low numbers of hornworm larvae may be tolerated with a minimal effect on yield. In small gardens, larvae can be removed by hand. The horn presents no danger. Also, white cocoons can often be seen on the hornworm larvae back. These are braconid parasites and eventually kill the larvae. Leaving infested larvae will propagate the beneficial parasite. In commercial tomato fields, most registered insecticides are effective against hornworm larvae.
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Tomato: Twospotted spider mite, Tetranychus urticae Koch, Acari, Tetranychidae
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Photo 162 |
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Photo 163 |
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Photo 164 |
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Photo 165 |
Biology: Adult spider mites are minute (<.5 mm in length) and possess 8 legs and are thus, not true insects. Immatures resemble adults and feed by extracting sap from the bottom of tomato leaves. The result of this feeding is a whitish or bronze appearance on the leaves (Photo 162). When large numbers of mites are present, silk webbing can be seen on leaves, stems, blooms and fruit (Photos 163, 164 and 165). Adult females deposit up to about 100 eggs on the bottoms of tomato foliage. Larvae emerge in as few as 3 days and begin to feed. Within about 1 week adults may appear and the cycle is repeated. Multiple generations occur each year. Hot dry weather promotes mite increase.
Management: Shortly after transplanting, tomato plants should be scouted for mites. Low numbers of mites may be tolerated with a minimal effect on yield. If mite numbers increase beyond acceptable levels, use of an acaricide such as Kelthane is warranted. Mites feed predominately on the bottoms of tomato foliage. Thus, acaricides must be applied in such a manner in which the mite comes into contact with the insecticide, i.e., apply the acaricide to the leaf bottom. Use of a surfactant and a large volume of water should assist the spread of the material to the bottom surface. Spider mites often occur in only small areas within the field. Management may be directed at these areas but movement from infested areas into other points within the field should be controlled. In areas with a history of high mite numbers, removal of adjacent weeds several weeks prior to transplanting, may reduce later infestations.
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Tomato: Stink bugs, Hemiptera: Pentatomidae and Coreidae
Biology: Stink bugs are true bugs having the front half of the fore wing hardened while the rear portion is membranous. Adult size and color vary greatly by species. Pentotamids (Photo 166) are shield shaped about 15mm long while Coreids are more oblong and are up to 25mm long. Some have flattened expansions on the hind legs and are termed leaf-footed bugs (Photo 167). Immature stink bugs or nymphs resemble the adults but are wingless. Stinkbugs feed on most of the tomato plant but damage is most evident on fruit. A beak-like stylet is inserted into the plant tissue, digestive fluids are injected and plant sap is withdrawn. On fruit, this leaves a very small scab on the surface. Fruit damaged during early stages of formation may be distorted. Two generations occur each year.
Management: Low numbers of stink bugs may be tolerated with a minimal effect on yield. If stink bug numbers increase beyond acceptable levels, use of insecticides may be warranted. Sanitation, including destruction of crops immediately following the last harvest, may have some effectiveness in reducing damage in subsequent plantings. Numerous beneficial organisms affect stink bug populations including some beneficial stink bugs and insecticide use may reduce their effectiveness. In commercial fields, high stink bug populations will likely require use of insecticide sprays.
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Tomato: Thrips, Frankliniella occidentalis (Pergande) and Thrips tabaci Lindeman, Thysanoptera: Thripidae
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Photo 168 |
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Photo 169 |
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Photo 170 |
Biology: Thrips are minute insects found on the blooms and leaf surfaces of tomato. Adults are dark brown to black and about 1mm long (Photo 168). Two pairs of wings are present and long hairs occur on the edges of the wings (Photo 169). Immature thrips are smaller and lighter in color. Adults and immature stages “rasp” the leaf surface with their mouthparts and feed on the exuding plant sap. The impact of thrips on tomato in Arkansas is usually minor but large populations of thrips can cause yellowing of foliage and stunting of tomato. More importantly, thrips transmit Tomato Spotted Wilt Virus (TSWV) (Photo 170). After mating, females insert eggs into the plant tissue. Larvae emerge and feed by scraping the plant surface and ingesting plant sap. Maturity is reached in less than one week and pupation occurs in soil. Adults emerge in about four days and the cycle is repeated. Many generations occur annually in Arkansas.
Management: Use of insecticides applied for thrips management in order to reduce the occurrence of TSWV is debatable. While within field spread of the virus may be reduced, insecticide use likely has little affect on preventing introduction of the virus into the field. In the absence of TSWV, low numbers of thrips on tomato may be tolerated with a minimal effect on yield. If insecticides are used, systemic insecticides may provide more effective control. These include acetamiprid and imidacloprid. Sanitation, including destruction of crops immediately following the last harvest, may have some effectiveness in reducing damage in subsequent plantings.
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Tomato: Tomato pinworm, Keiferia lycopersicella (Walsingham), Lepidoptera: Gelichiidae
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Photo 171 |
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Photo 172 |
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Photo 173 |
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Photo 174 |
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Photo 175 |
Biology: Pinworm adults emerge from pupae that occur in the upper soil surface. The adult moth is minute and about 6 mm in length and with a wingspan of about 10 mm (Photo 171). Color is gray to tan. After mating, eggs are laid and larvae hatch in about 1 week depending on temperature. Each female moth can lay about 50 eggs. Larvae feed on most parts of the tomato plant including foliage, flowers, small stems and fruit. On foliage, larvae mine into the surface and mines are often expanded until a large blotch is formed (Photo 172). Larvae also enter fruit near the calyx and feed within (Photos 173, 174 and 175). Upon maturation, larvae chew an exit hole that is often the most noticeable damage on tomato fruit. Larvae crawl to the ground where pupation occurs. Many generations occur each season. As these overlap, damaging larvae can occur throughout the tomato production season.
Management: In Arkansas, occurrence of tomato pinworm has been very low and management has not been required. If numbers increase beyond acceptable levels, application of insecticides may be required. Sanitation, including destruction of crops immediately following the last harvest, will likely reduce damage in subsequent plantings. Beneficial insects including Trichogramma also may play an important role in tomato pinworm management and proper insecticide selection and use will increase the effectiveness of beneficials.
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