Watch for Thrips in Row Crops

Many species of thrips (in the insect order Thysanoptera) infest corn, soybean and cotton crops. The distinguishing feature setting them apart from other insect pests is that thrips thrive on dozens of plant types; most crops, including vegetables, flowers, forages, field and orchard crops, are attacked by at least one species of thrips.

Identification and Lifecycle

Thrips are tiny, slender, agile insects. They rarely exceed 0.4 to 0.6 inches in length, depending on the species and the crop they infest. Typically, thrips vary in color from black, yellowish-brown, tan and sometimes orange. Their uneven mouthparts are cone-shaped, and wings are narrow and fringed with hairs. When thrips target host plants, they feed by gnawing (rasping) on leaves and plant tissues to release sap that they consume.

Thrips appear on growing plants primarily in spring and summer in most geographies. Identification and lifecycle characteristics of thrips vary somewhat by the host crop or plant they attack.

Corn

Grass thrips are the most common thrips species infesting corn. Grass thrips feed on leaf cells by penetrating leaves and sucking out the cell contents. Both immature thrips and adults will feed on leaves. Adult corn thrips appear black in color, while immature thrips are lighter in color and smaller in size.

Thrips often overwinter on wheat and maturing weeds. Adult thrips migrate into field corn in the spring and early summer. Adults mate, and females inject eggs into young corn seedling tissue. In about five days under warm weather conditions, eggs hatch as larvae and feed on the leaf surface by gnawing cells and sucking sap. Adults may produce several generations each year.

Soybeans

Thrips in soybeans are not often noticed, yet they are among the most numerous soybean insect pests. They are tiny insects with thin bodies. Adult soybean thrips differ from immature thrips because they fold two pairs of wings behind their backs unless in flight. Adults range in color from black to yellow.

Typically producing several generations per year, soybean thrips overwinter as larvae or adults on hosts such as weeds and neighboring crop residue. They move onto soybean seedlings immediately after emergence. Most soybean thrips develop from egg to adults in 10 to 30 days, depending upon air temperatures. It’s common for a female adult to hatch 30 to 300 eggs.

Soybean thrips also act as a vector for transmission of soybean vein necrosis virus (SVNV) from plant to plant. In recent years, the disease has been documented in at least 16 states, so it’s important to monitor for high thrips populations that can spread SVNV. The disease is a relatively new soybean threat; it was first detected in 2008 in Tennessee.

Cotton

Thrips may be found in cotton plants throughout the growing season, but early-season seedlings are most susceptible during cool, wet weather. Common thrips species in cotton vary by region. Farmers should check regional guides and management recommendations for the thrips that dominate in their fields. Similar to thrips in other field crops, thrips in cotton use their rasping and sucking mouthparts to invade young seedlings and feed on the liquids in plant tissues.

Eggs hatch in about six days after the female thrips’ sharp laying tube inserts them into cotton plants. This is followed by two larval stages, which take six days. Another four days are needed for the pupating process. The lifecycle involves about 16 days from egg to mature adult. Each female produces 50 eggs or more, and their lifespan averages 35 days.

Crop Damage

Corn

The tiny, long, white scars in plant tissue caused by thrips can make leaves turn gray and destroy photosynthesis. When corn plants are stressed for water during long stretches of hot, dry weather, the most damage from corn thrips can occur. Corn during the seedling and ear development stage are most vulnerable to thrips injury. Although corn thrips are considered an occasional pest, large populations of corn thrips can cause leaves to turn yellow and stunt seedling growth. Thrips can be found in corn throughout the growing season. Typically, thrips themselves do little damage, but they create penetration into corn kernels that allows Fusarium spp. infection and disease, resulting in ear rot.

Soybeans

The soybean seedling stage (VE to V6) presents the most risk from economic damage caused by thrips. White to yellow spots on soybean seedling leaves may appear when thrips are feeding. Poor plant vigor and stunting may result. Although rare, seedlings may die under high soybean thrips populations, which can cause leaf crinkling. The threat of soybean thrips damage increases during hot, dry weather.

Cotton

The early, slow growth of the terminal bud makes cotton more susceptible to thrips yield damage than corn or soybeans. Cotton plants are most likely to be harmed by thrips from emergence to the third or fourth leaf stage. They may develop high populations in cotton grown near corn and small grains such as wheat. After the third or fourth leaf stage, cotton plants should be in a vigorous growth mode and relatively secure from thrips yield damage.

Feeding thrips strike cotton leaves and terminal buds. Stunted plants can result from thrips feeding, which destroys plant cells and causes crinkled leaves that curl upward. When populations are severe, terminal buds may be destroyed and excessive branching may slow cotton growth. Long-term research indicates thrips are best controlled early with a pre-applied seed treatment, an insecticide applied in-furrow at planting or a foliar insecticide applied as needed after seedlings emerge.

Best Management Practices to Control Thrips in Corn

Weed Control

Crop residue and weeds provide an environment for insects, such as thrips, to thrive. Pre-plant and pre-emergence herbicides with residual activity, tillage and season-long weed control, as needed, can help minimize insect threats.

Scouting

Because thrips are so tiny, they’re difficult to see. Immature thrips are lighter in color, while adults will have two pairs of wings. Scout early after crop emergence and throughout the growing season. The most obvious signs of thrips to scout for are foliage yellowing and seedling stunting. Refer to university Extension weekly and monthly reports for scouting guidelines and economic thresholds for insecticide treatments in specific corn varieties.

Insecticides

Follow integrated pest management (IPM) guidelines for corn and always rotate insecticides with different modes of action to effectively manage insecticide resistance in combination with other control practices.

For information on a portfolio of products from Bayer that help corn growers maximize yields and protect their crops, contact your local Bayer representative.

Always read and follow label instructions. Not all products are registered for use in every state.

Best Management Practices to Control Thrips in Soybeans

Seed treatments

The best approach to managing thrips and other insects in soybeans is preventative control. Starting off with a good seed treatment is an excellent way to control insects and protect soybean plants above and below the ground. Under low to moderate pressure, seed treatments labeled for thrips will go a long way to protect young seedlings from chewing (rasping) damage to soybeans.

Weed Control

Crop residue and weeds provide an environment for insects, such as thrips, to thrive. Pre-plant and pre-emergence herbicides with residual activity, tillage and season-long weed control, as needed, can help minimize insect threats.

Scouting

Begin scouting for thrips early in the seedling stage, during the VE to V6 growth stages. Select 50 plants randomly within a field. Use a hand lens to look for thrips and inspect fifth trifoliate leaves for feeding damage. Consider the extent of crop damage. Unless 75 percent of trifoliate leaves are damaged, treatment is not likely to be economically practical and could possibly lead to spider mite infestations. Refer to university Extension weekly and monthly reports for scouting guidelines and economic thresholds for insecticide treatments in specific soybean geographies.

Soybean insecticides

Usually, soybean seedlings will outgrow thrips injury, and an insecticide treatment is not needed. Evaluate if 75 percent of leaves sampled are damaged. If so, an insecticide application for soybean thrips may be advisable. Baythroid^® XL, a pyrethroid, performs on a broad spectrum of insect pests, with fast knockdown and long residual control. Baythroid XL may be used throughout the growing season; however, application timing should be based on careful scouting and local economic thresholds. Follow IPM guidelines for soybeans and always rotate insecticides with different modes of action to effectively manage insecticide resistance in combination with other control practices.

For information on a portfolio of products from Bayer that help soybean growers maximize yields and protect their crops, contact your local Bayer representative.

Always read and follow label instructions. Not all products are registered for use in every state. Baythroid XL is a Restricted Use Pesticide.

Best Management Practices to Control Thrips in Cotton

Seed Treatments

The best approach to managing thrips and other cotton insects is preventative control. Starting off with a good seed treatment is an excellent way to control insects above and below the ground. Under low to moderate pest pressure, seed treatments labeled for thrips will go a long way to protect young seedlings from chewing (rasping) damage to cotton. The Bayer portfolio of seed treatment products for cotton offers the best seed treatment, seedling disease protection, early-season insecticide and nematicide control available on the market today.

For areas with a history of early-season insect infestations, growers can use Aeris^® insecticide/nematicide seed treatment, which offers broad-spectrum protection against thrips as well as cutworms and reniform and root knot nematodes. Aeris offers growers two effective modes of action against thrips to ensure protection and manage resistance development. Aeris is the preferred insecticide/nematicide partner to Trilex^® Advanced, a premium fungicide seed treatment.

Weed Control

Crop residue and weeds provide an environment for insects, such as thrips, to thrive. Pre-plant and pre-emergence herbicides with residual activity, tillage and season-long weed control, as needed, can help minimize insect threats.

Scouting

Start checking weekly for thrips from about the time cotton emergence reaches a 50 percent stand until squaring begins and plants have five to seven leaves. Heavy populations of thrips can migrate from nearby weeds and crops, especially wheat. It only takes a few days for the pests to significantly injure plants before the true leaves appear. Because thrips often hide in tight spots, closely scout by uncurling all the leaves in the terminal growth. Check four sections within a field, examining 25 plants. Look for thrips and feeding symptoms on upper and under leaves, especially between leaf veins. Refer to university Extension weekly and monthly reports for scouting guidelines and economic thresholds for insecticide treatments in specific cotton geographies.

Cotton Insecticides

In-furrow insecticide treatment is recommended in fields with known high infestations of cotton thrips. Cotton growers can use an in-furrow, at-plant insecticide/nematicide such as Velum^® Total, which delivers wide-spectrum, long-lasting control of nematodes and early-season cotton insects, including thrips, aphids and fleahoppers.

While foliar applications after heavy thrips damage will not usually increase cotton yields, early application once thrips are detected can help avoid a negative impact on yield. Baythroid^® XL insecticide, a pyrethroid, performs on a broad spectrum of insect pests, with fast knockdown and long residual control. Follow IPM guidelines for cotton and always rotate insecticides with different modes of action to effectively manage insecticide resistance in combination with other control practices.

For information on a portfolio of products from Bayer that help cotton growers maximize yields and protect their crops, contact your local Bayer representative.

^{Always read and follow label instructions. Not all products are registered for use in every state. Baythroid XL is a Restricted Use Pesticide.}