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Extension Entomology

Lesser Cornstalk Borer

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Article author: Kate Crumley
Most recently reviewed by: Tyler Mays & Danielle Sekula (2021)

Common Name(s): Lesser Cornstalk Borer

Description

The lesser cornstalk borer is a small, yellow to black moth with sexual dimorphism that varies by location. This moth species is a pest on a variety of grain and legume crops, with larvae that feed by tunneling into the stem of the host plant.

Origin and Distribution

The lesser cornstalk borer is native to the United States. It can be found from Maine to California, and has been documented in Hawaii, but is most often found in sandy soils in the southeastern United States. It can also be found in Mexico, Central, and South America.

Habitat & Hosts

The lesser cornstalk borer is a polyphagous pest that feeds on a variety of crops. Vegetable and legume crops are often damaged, and it has a variety of weedy hosts like crabgrass, johnsongrass, wild oats, bermudagrass, wiregrass, goosegrass, and nutsedge.

Life Cycle

Lesser cornstalk borer eggs are oval, and are 0.35mm – 0.43 mm in width, and green when first laid, but turn pink after 8- 24 hours. Eggs turn deeper red as they near hatching, and are a deep iridescent crimson immediately before. Eggs take between 2- 3.5 days to hatch depending on temperature. Larvae that can be found in silk tunnels radiating horizontally from the stems of their host plants immediately below the soil surface. The silk tubes are usually between two or three inches long, depending on the age of the larvae. Larvae normally have 6 instars, but can range from 5- 9, and range from 1.3 mm to 20.8 mm long. The larval stage lasts about 20 days when not overwintering. Pupae can be found in the silk tunnels near base of the plant, or loose in the soil. They are yellow early, and turn dark brown to nearly black before adults eclose. They range from 7.6 mm to 9.6 mm in length. The pupal stage can last from 7- 10 days when not overwintering. Adult moths are 8-9 mm long brown moths with sexual dimorphism, and color patterns that vary based on location. Adults live for about 10 days, and are most active at night.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Damage from the lesser cornstalk borer is caused by feeding, which tunnels into the stem of the plant or girdles the base of the plant. Wilting is one of the early symptoms of infestation, and can result in a poor crop stand. Insecticides can be used to control this pest, but need to be applied to the root zone, either in the seed furrow or banded over the seed bed. Modified planting practices can be used to minimize damage. Insect populations increase later in the growing season, so early planting can help. Tillage and weed control also help minimize insect populations in the environment, but conservation tillage can also help. Conservation tillage can allow larvae to feed freely on crop residue and organic matter, which can spare seedlings.

Related Publications

http://entnemdept.ufl.edu/creatures/field/lesser_cornstalk_borer.htm#damage

https://entomology.ca.uky.edu/ef129

Citations

All JN, Gallaher RN, Jellum MD. 1979. Influence of planting date, preplanting weed control, irrigation, and conservation tillage practices on efficacy of planting time insecticide applications for control of lesser cornstalk borer in field corn. Journal of Economic Entomology 72: 265-268.

Bessin R. 2004. The common stalk borer in corn. University of Kentucky, Entomology. University of Kentucky, Lexington, KY. http://www.ca.uky.edu/entomology/entfacts/ef100.asp (5 September 2008)

Biddle AJ, Hutchins SH, Wightman JA. 1992. Pests living below ground, Elasmopalpus lignosellus: Lesser cornstalk borer, pp. 202-203. In McKinley RG. [editor] Vegetable Crop Pests. CRC press, Boca Raton, FL.

Capinera JL. 2001. Handbook of Vegetable Pests. Academic Press, San Diego. 729 pp.

Chang V, Ota AK. 1987. The lesser cornstalk borer: a new important pest of young sugarcane, pp. 27-30 In Annual Report, 1986. Experiment station. Hawaiian Sugar Planter’s Association, Pahala, HI.

Chapin JW. (1999). Lesser cornstalk borer on peanut. Entomology insect information Series. http://entweb.clemson.edu/eiis/pdfs/ag21.pdf (20 August 2008).

Funderburk JE, Boucias DG, Herzog DC, Sprenkel RK, Lynch RE. 1984. Parasitoids and pathogens of larval lesser cornstalk borers (Lepidoptera: Pyralidae) in northern Florida. Environmental Entomology 13: 1319-1323.

Funderburk JE, Herzog DC, Mack TP, Lynch RE. 1985. Sampling lesser cornstalk borer (Lepidoptera: Pyralidae) adults in several crops with reference to adult dispersion patterns. Environmental Entomology 14: 452-458.

Gardner WA, All JN. 1982. Chemical control of the lesser cornstalk borer in grain sorghum. Journal of Georgia Entomological Society. 17: 167-171.

Isely D. 1944. The lesser cornstalk borer, a pest of fall beans. Journal of Kansas Entomological Society. 17: 51-57.

Leuck DB. 1966. Biology of the lesser cornstalk borer in south Georgia. Journal of Economic Entomology 59: 797-801.

Luginbill P, Ainslie GG. 1917. The lesser cornstalk borer. U.S. Department of Agriculture Bulletin 539. 27 pp.

Lynch RE, Klun JA, Leonhardt BA, Schwarz M, Garner JW. 1984. Female sex pheromone of the lesser cornstalk borer, Elasmopalpus lignosellus (Lepidoptera: Pyralidae). Environmental Entomology 13: 121-126.

Mack TP, Backman CB. 1984. Effects of temperature and adult age on the oviposition rate of Elasmopalpus lignosellus (Zeller), the lesser cornstalk borer. Environmental Entomology. 13: 966-969.

Mack TP, Davis DP, Backman CB. 1991. Predicting lesser cornstalk borer (Lepidoptera: Pyralidae) larval density from estimates of adult abundance in peanut fields. Journal of Entomological Science 26: 223-230.

Mack TP, Davis DP, Lynch RE. 1993. Development of a system to time scouting for the lesser cornstalk borer (Lepidoptera: Pyralidae) attacking peanuts in the southeastern United States. Journal of Economic Entomology 86: 164-173.

Metcalf CL, Flint WP, Metalf RL. 1962. Lesser cornstalk borer, pp. 497-498. In Destructive and useful insects. McGraw-Hill Book Company, San Francisco, CA.

Nuessly GS, Webb SE. (2007). Insect management for sweet corn. EDIS. http://edis.ifas.ufl.edu/IG158 (7 May 2020).

Riley CV. 1882. The smaller corn stalk-borer. U. S. Department of Agriculture Report 1881: 142-145.

Sanchez, Louis O. 1960. The biology and control of the lesser cornstalk borer, Elasmopalpus lignosellus.

Schaaf AC. 1974. Jumping borer, Elasmopalpus lignosellus, pp. 31-34. In Handbook of pests of sugarcane. Tech Bull 1/75. Sugar Industry Research Institute Mandeville, Jamaica.

Smith JW Jr, Barfield CS. 1982. Management of preharvest insects, pp. 250- 325. In Pattee HE, Young CT (editors), Peanut science and technology. American Peanut Research Education Society, Yoakum, TX.

Smith Jr JW, Johnson SJ, Sams RL. 1981. Spatial distribution of lesser cornstalk borer eggs in peanuts. Environmental Entomology 10: 192-193.

Smith Jr JW, Johnson SJ. 1989. Natural mortality of the lesser cornstalk borer (Lepidoptera: Pyralidae) in a peanut agroecosystem. Environmental Entomology 18: 69-77.).

Tippins HH. 1982. A Review of Information on the Lesser Cornstalk Borer Elasmopalpus lignosellus (Zeller). Georgia Agricultural Experiment Station Special Publication 17. 65 pp.

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Spotted wing drosophila

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Article author: Ballinger (Vacant)
Most recently reviewed by: Danielle Sekula & Tyler Mays (2021)

Common Name(s): cherry vinegar fly, Spotted wing drosophila

Description

The spotted wing drosophila (SWD) is a fruit fly that is a 1/16 to 1/8 inch long with red eyes and a yellow-brown thorax and abdomen. There are black stripes down its abdomen. The adult males have a single black spot on the tip of each wing, but the females lack this distinctive marking, making it difficult to identify this insect.

The adults and larvae closely resemble the common vinegar fly, D. melanogaster, as well as other Drosophila species that attack mostly rotting or fermenting fruit. However, the SWD prefers healthy, ripening fruits.

Origin and Distribution

The spotted wing drosophila is native to Asia and is found throughout most of the fruit producing states in the U.S. The distribution map below shows counties in which SWD has been reported using EDDMaps. If you find SWD in your area, please consider reporting to EDDMaps.

Habitat & Hosts

The spotted wing drosophila prefers healthy, ripening fruits. They are commonly found on thin-skinned, soft fruits such as strawberries, blackberries, raspberries, blueberries, cherries, and plums. They can also be found on apples and pears, but only if these fruits become damaged. SWD have also been found on other hosts such as mulberry and honeysuckle.

 

Life Cycle

Adult spotted wing drosophila on raspberry.

Adult spotted wing drosophila on raspberry. Photo credit: University of Minnesota Extension.

The spotted wing drosophila can complete its life cycle in 1-2 weeks, depending on environmental conditions. SWD are most active at temperatures above 68°F, but will decrease laying eggs in temperatures above 86°F. The SWD can have multiple generations per year and females can lay up to 300 eggs in her lifespan.

The female SWD penetrates the skin of the fruit with her serrated ovipositor and lays her eggs under the skin, causing a small puncture or “sting”. A female can lay 1-3 eggs in these puncture sites and they will hatch in 2-72 hours. The larvae tunnel and feed inside the fruit for 5-7 days. They then pupate inside or outside the fruit which lasts from 3-15 days and emerge as adult flies. The SWD overwinters as adults.

The damage from SWD is initiated when the females use their ovipositor to cut through the fruit skin leaving a small scar that is sunken in. The damage is primarily done by larval feeding which causes the fruit to turn brown and soft. This causes the fruit to collapse due to internal rots and damage caused by mold or secondary infections.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

In order to determine if you have SWD present, monitor your garden for adult flies as soon as the fruit starts to set until the end of harvest. The most important time to monitor is when fruit color first starts to develop until harvest.

There are some cultural control practices that can help reduce the buildup of SWD populations. Removing any infested or overripe fruit, wild host plants such as mulberries and grapes nearby your field or garden, and ensuring a timely harvest are all important in reducing SWD populations. Early harvest of fruit can be important in reducing the exposure of fruit to the SWD. Begin harvest as early as you can and continue to remove fruit as they ripen. Another example of a cultural control method that can be used to manage SWD is the use of netting or floating row covers. The covers prevent SWD access to developing fruits and can potentially reduce the infections.

Since the SWD will complete multiple, overlapping generations, there is continuous activity once the flies become active. The insecticides only target the adults and will not control the larvae already in the fruit since they are protected by the fruit. Insecticides used for SWD include organophosphates and synthetic pyrethroids, as well as spinosyn but it has shown lower activity and residual control. It is important to read and follow the label restrictions of insecticides applied if you to intend to consume or sell what you harvest.

Citations

Caprile, J.L., Flint, M.L., Bolda, M.P. Spotted Wing Drosophila. University of California Statewide IPM Program: Pest Notes 74198. http://ipm.ucanr.edu/PDF/PESTNOTES/pnspottedwingdrosophila.pdf

Carroll, Juliet. 2017. Spotted Wing Drosophila. New York State Integrated Pest Management Program- Cornell University. https://ecommons.cornell.edu/bitstream/handle/1813/42883.3/spotted-wing-drosoph-NYSIPM.pdf?sequence=6&isAllowed=y

Burrowing Bug

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Article author: Tyler Mays
Most recently reviewed by: Kerry Siders & Ballinger (Vacant) (2020)

Common Name(s): Burrower Bug, Burrowing Bug, Peanut Burrower Bug

Description

The burrower bug is a soil dwelling insect only leaving the soil to migrate to new locations within a field or a nearby field. Their presence and damage is favored by hot and dry weather conditions. Feeding damage by this insect can reduce the quality of peanuts, and in other crops rarely cause economic damage.

Adult burrower bugs are small, roughly ¼” in size and resemble a small stink bug. Adults are black with the tips of the forewings being clear and membranous. Legs of adults are covered in spines.

Immature insects can range in color depending on the exact species of the insect. The immature peanut burrower bug has a grey-tan abdomen with three black spots on the back that are oval in shape.

Habitat & Hosts

Burrower bugs are known to feed on a variety of plants including peanut, soybean, cotton, conr, peppers, strawberry, spinach, oak trees, peach, pear, and more. Burrower bugs occur in high numbers around lights at night during periods in the fall. They can be a pest of crop production and found throughout Texas. This insect is medically harmless.

 

Life Cycle

The burrower bugs belongs to the order Hemiptera, and has an incomplete life cycle (hemimetabolous). The adult female lays its eggs at or just below the soil line and once hatched the nymph resembles the adult without wings. As the insect develops through five instars in the nymph stage, its wings will slowly form. In Texas there appears to be two peaks in the population with the first occurring in mid May to June and the second occurring in late July to August.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

The soil dwelling habitat of this insect makes management options complicated. Avoiding dry soil conditions through irrigation will minimize the presence and severity of damage caused by this insect. In row crops chlorpyrifos can be applied, but this insecticide is currently under EPA review and may not be available in the near future. Other insecticides options include bifenthrin, imidacloprid, and/or lambda-cyhalothrin; however, little data has been conducted on the efficacy of these insecticides against the burrower bug. Additionally, the entomopathogenic nematode Heterohabdities bacteriophora has been identified as a potential biological control agent.

Burrower bug damage to peanut kernals. Photo by Steve L. Brown, University of Georgia, Bugwood.org.

Burrower bug damage to peanut kernals. Photo by Steve L. Brown, University of Georgia, Bugwood.org.

Citations

Martini, Xavier and David Wright. 2017. The Peanut Burrower Bug-an Emerging Pest In Peanuts. Feb. 17, 2017. Field Crops, Insects, Peanut, Pest Management. nwdistrict.ifas.ufl.edu/phag/2017/01/17/the-peanut-burrower-bug-an-emerging-pest-in-peanuts

Baughman, Todd, Peter Dotray, James Grichar, Mark Black, Jason Woodward, Calvin Trostle, Scott Russell, Clyde Crumley, Pat Porter, Leon New, Paul Baumann, Mark McFarland. Texas Peanut Production Guide. texaspeanutboard.com/wp-content/uploads/peanutproductionguide.pdf

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Chilli Thrips

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Article author: Extension Entomologist at Weslaco (Vacant)
Most recently reviewed by: Pat Porter & Extension Entomologist at Overton (2020)

Common Name(s): Chilli Thrips, Strawberry Thrips, Yellow Tea Thrips

Description

Chilli thrips, Scirtothrips dorsalis, are tiny (> 2mm long), cigar-shaped insects.  The adults are pale in color with black, feathery wings and dark spots forming incomplete stripes on the top of the abdomen.  Immatures, called larvae, look similar to adults but are even smaller and lack wings. Distinguishing chilli thrips from other thrips species is difficult, requires magnification, and some knowledge of insect taxonomy.  Chilli thrips are most often recognized based on their behavior and the type of damage they cause.

Origin and Distribution

Chilli thrips are thought to originally come from Southeast Asia although they are now widely distributed through most of the world including India, Japan, most of Africa, much of the Caribbean and South America, and are quickly becoming established in the United States.  They were first detected in Florida in 1991 and in Southeast Texas in 2005.  They have been intercepted at various ports-of-entry many times on a wide range of host plants and are likely established in many landscapes from Florida to Texas.  This insect has the potential to become a wide-spread pest throughout the Southern and Pacific U.S.

Habitat & Hosts

Chilli thrips are known to infest an impressively wide range of host plants, more than 225 species from at least 40 different plant families, and the list will likely continue to grow as they expand their range.  Their main wild, or native, host plants are in the bean family, Fabaceae.  Among other known plant hosts are numerous important crops and ornamental plants such as citrus, corn, cotton, eggplant, melon, peanut, pepper, rose, strawberry, tobacco, and tomato.

Unlike similar looking species such as the Western flower thrips, which are often found in flowers feeding on pollen, chilli thrips feed on foliage and are typically found on the undersides of leaves near the mid-vein or borders of leaves. However, when population densities are high, some individuals may be found feeding on the upper surface of leaves.

 

These insects have piercing and sucking mouthparts they use to extract material from individual epidermal plant cells.  Cell death leads to a silvering or bronzing of leaves and may cause them to curl, distort and/or turn brittle and drop from the plant.  Infested plants can become stunted or dwarfed. Chilli thrips tend to favor tender plant tissue, flower buds, and young fruits and vegetables although all above ground parts of plants may be attacked.  Feeding on fruits leads to scarring and, in severe infestations, corky tissues.  Aesthetic damage to ornamental plants can lead to extensive losses in the nursery/horticultural industry.

In addition, chilli thrips are known to vector at least seven viruses to various plants including chilli leaf curl virus, peanut necrosis virus, tobacco streak virus, melon yellow spot virus, watermelon silver mottle virus, and capsicum chlorosis virus, although there are no reports at this time that they have been vectors of any of these viruses in Texas.

Life Cycle

Female thrips insert anywhere from 60 – 200 microscopic, kidney-shaped eggs into plant tissue on or near leaf veins, terminal plant parts and floral structures where they cannot be detected by the naked eye.  Eggs will hatch in 2-7 days.  There are two larval stages that look similar to the adult but are smaller and lack wings.  Larvae feed for 8-10 days before entering a non-feeding pupal stage that lasts 2-3 days.  The length of time it takes to complete their life cycle varies depending on temperature and host plant but ranges from 14 – 20 days.  Their large reproductive capacity and quick generation time means that chilli thrips populations can increase very quickly.

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Early detection of chilli thrips is important.  Monitor for leaf silvering, bronzing or distortion, which can be mistaken for herbicide damage.  To sample for thrips, tap the terminal portion of plants over a white piece of paper and examine with a hand lens or magnifying glass.  In nurseries or greenhouses, yellow or blue sticky traps can be used to monitor for thrips.

Chilli thrips do have some natural enemies including minute pirate bugs (Orius sp.), lacewings, and predatory mites.  While these predators may not always be able to provide adequate control of chilli thrips, it is important to preserve them by avoiding broad-spectrum insecticides such as pyrethroids and organophosphates, both of which also have a limited ability to manage chilli thrips .  Biorational insecticides including horticultural oils, spinosad, and insecticidal soaps will kill larvae and adult thrips but have no residual activity so frequent application will be needed to control larvae as they emerge from eggs and/or new thrips migrate in.  Products containing the conventional insecticide imidacloprid can be used as a soil drench or foliar spray and will provide control for a longer period of time with minimal impact on natural enemies. No matter what product you choose, it is important to rotate between different insecticide modes of action to reduce the risk of developing insecticide resistance.

Contributors: Scott Ludwig and Carlos Bogran

Related Publications

Chilli Thrips Control, Identification, and Management. 2016. Yan Chen, Steven Arthurs and Dennis Ring. LSUAg. Available here

Featured Creatures. Chilli Thrips. UF IFAS University of Florida. Available here

Pest Thrips of the United States: Field Identification Guide. Available here

Citations

Ananthakrishnan T. N. 1993. Bionomics of thrips. Annual Review of Entomology 38: 71-92

Chiemsombat, P., O. Gajanandana, N. Warin, R. Hongprayoon, A. Bhunchoth, P. Pongsapich. 2008. Biological and molecular characterization of tospoviruses in Thailand. Archives of Virology 153: 571-577.

Kumar, V., D. R. Seal, G. Kakkar, C. L. McKenzie, and L. S. Osborne. 2012. New tropical fruit hosts of Scirtothrips dorsalis (Thysanoptera: Thripidae) and its relative abundance on them in south Florida. Fla. Entomol. 95: 205 – 207.

Kumar, V., G. Kakkar, D. R. Seal, C. L.  McKenzie, J. Colee, and L. S. Osborne. 2014. Temporal and spatial distribution of an invasive thrips species Scirtothrips dorsalis (Thysanoptera: Thripidae). Crop Protection 55: 80 – 90.

Mound, L. A., and J. M. Palmer. 1981. Identification, distribution and host plants of the pest species of Scirtothrips. (Thysanoptera: Thripidae). Bulletin of Entomological Research 71: 467-479.

Rao, R. D., V. J. Prasada, A. S. Reddy, S. V. Reddy, K. Thirumala-Devi, S. Chander Rao, V.Manoj Kumar, K. Subramaniam, T. Yellamanda Reddy, S. N. Nigam, D. V. R. Reddy. 2003. The host range of tobacco streak virus in India and transmission by thrips. Annals of Applied Biology 142: 365-368.

Reddy, D. N. R., and Puttswamy. 1983. Pest infesting chilli (Capsicum annuum L.) in the nursery. Mysore J. Agric Sci 17: 246 – 251.

Sanap, M. M., R. N. Nawale, 1987. Chemical control of chilli thrips, Scirtothrips dorsalis. Vegetable Science 14: 195 – 199.

Seal, D. R., M. Ciomperlik, M. L. Richards, W. Klassen. 2006. Distribution of the chilli thrips, Scirtothrips dorsalis Hood (Thysanoptera: Thripidae), within pepper plants and within pepper fields on St. Vincent. Florida Entomologist 89: 311-320.

Seal, D. R., W. Klassen, and V. Kumar. 2010. Biological parameters of Scirtothrips dorsalis (Thysanoptera: Thripidae) on selected hosts. Environ. Entomol. 39: 1389 – 1398.

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Corn Earworm (Helicoverpa zea)

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Article author: Pat Porter
Most recently reviewed by: Dalton Ludwick & Extension Entomologist at Weslaco (Vacant) (2020)

Common Name(s): Corn earworm, Cotton Bollworm, Soybean Podworm, Tomato Fruitworm

Description

Corn earworm belongs to the Order Lepidoptera (butterflies, moths and skippers) and the adult stage is a stout bodied, brownish to buttery-yellow moth with a wingspan of about 1 1/4 to 1 1/2 inches. There are usually darker bands present near the tips of the front and hind wings.

There are six larval instars (or stages). The first instar is about 1/16” long and the the 6th instar can grow to 1 3/4 inches long. There is no one color for the larvae, and they can range from yellow to pink to green. Regardless of coloration there will be a darker stripe down the midline of the top of the larva, and somewhat wider stripes on the lateral edges of the body when viewed from above. A yellowish band is often found on the side of the larvae, and the band contains the dark, circular spiracles, the holes that let air into the insect’s body. Larvae have many microspines on the back and sides of the body, and these are not found on other common corn caterpillar pests. The head is orange to tan but may be more brownish in some larvae.

Origin and Distribution

Corn earworm is native to the New World and overwinters in Texas, has multiple generations here, and is a threat throughout the growing season. In the United States, it is thought to be able to overwinter south of about 40 degrees north latitude, but as the summer progresses the moths fly north and infest the entire country and some of  Canada.

Corn earworm adult

Corn earworm adult showing typical buttery yellow color.

Habitat & Hosts

Corn earworm has an extremely wide food host range and can be found wherever its host plants grow. There are many non-crop plants on which the earworm can develop early in the year before crops and gardens are planted. Cultivated hosts include sweet corn, field corn, green beans, snap beans, cowpea, peas, peppers, eggplant, lettuce, sweet potato, rice, cotton, grapes, strawberry and many others. Typically the “worm” in sweet corn is the corn earworm. Corn earworm is also a very significant pest in hemp or cannabis production, and it is not uncommon to find larvae consuming buds and leaves.

Life Cycle

Eggs are laid singly on host plants. These are pearly white when laid and become somewhat more yellow over the course of the three days or so before they hatch. The larval stage, comprising six larval instars, lasts 12 to 15 days during the warm part of the growing season, longer when it is cooler. When fully grown, the 6th instar larvae leaves the host plant, burrows into the ground and enters the pupal stage which lasts 10 – 15 days during the summer. Adults emerge from the ground, mate and disperse to lay eggs. Sometimes they disperse very

Corn earworm egg on corn silk.

Freshly deposited corn earworm egg on corn silk.

long distances on storm fronts. Moths consume liquids and nectar as food and they are not damaging to plants.

 

 

Management

If you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.

Management practices differ depending on which crop is being damaged. On field corn and sweet corn, the eggs are laid on silks, and the newly hatched larvae feed down the silk channel and then on the tip of the ear. In this case there is little opportunity to use insecticides because the larvae are in protected spaces. If insecticides are to be used, then they should be applied at the time of egg laying, usually with repeated applications from the time of silking until after the brown silk stage is reached.

Control is more straightforward when the earworms are feeding on the outside of the leaf or fruiting structure. In this case, sprayable formulations of Bacillus thuringiensis can be applied if a least toxic control method is desired. It must be noted, however, that corn earworms are now resistant to many of the Bt toxins in these sprayable insecticides because they built up resistance to them on Bt (GMO) corn in the last 25 years that corn has been used in the US. Synthetic pyrethroids can be effective, especially on smaller larvae, but it is also the case that corn earworms have developed significant levels of resistance to synthetic pyrethroids due to their widespread use in agriculture. Chlorantraniliprole is highly effective on corn earworm larvae, even large larvae. Spinosad and Spinetoram are very effective as well, as is the old insecticide carbaryl (Sevin). Agricultural producers have more options available and should consult a crop-specific control guide.

Citations

Corn Earworm. University of Florida Featured Creature: http://entnemdept.ufl.edu/creatures/veg/corn_earworm.htm.

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