Cotton Insects

Cotton Insects agribegri

Cotton leaf damaged by thrips feeding.

The most consistent insect-related challenge for Kansas cotton growers is thrips. These tiny, barely visible, splinter-like insects are important pests during the first couple of weeks after plants emerge. They can retard growth but also are sometimes blamed for more damage than they cause.

Thrips are less than 2 millimeters long and vary in color from yellow to brown, gray or black. Adults have two pairs of narrow wings fringed with long hairs. They have rasping-sucking mouthparts, so they rasp the plant tissue and suck the liquids.

Most thrips problems in Kansas cotton seem to be related to thrips migrating from wheat as it matures in the spring. This may cause a burst of thrips activity that is particularly damaging if it occurs when the cotton plants emerge from the soil.

Thrips cause most damage to seedling cotton. They rasp tender leaves and terminal buds with their sharp mouthparts and feed on the juices. Leaves may turn brown on the edges, develop a silvery color, or become distorted and curl upward. Light thrips infestations tend to delay plant growth and retard maturity. Heavy infestations may kill terminal buds or even entire plants. Damaged terminal buds cause abnormal branching patterns. The duration and intensity of thrips infestations vary greatly according to season and geographic location. Once cotton plants are four to six weeks old, they outgrow thrips damage and recover.

Scouting for thrips can be quite difficult. However, it is important to catch significant populations before economic damage occurs. Start looking for thrips ,as soon as, plants begin to emerge, especially in the newest growth. Work on hands and knees. Shake plants over a piece of white paper. If you see small, slender objects crawling, these are usually thrips. If there is residue of sand or soil on the plants, the thrips will be more difficult to see. Windy conditions require pulling some plants, placing them in a plastic bag, taking them out of the wind and examining the plants for thrips in the terminals and on the underside of the first two leaves. Look for early signs of damage. Thrips feeding in the terminal tissue make new leaves appear ratty.

Populations above 1 thrips per true leaf up to the 6 leaf stage may justify treatment, depending on growing conditions. Control is rarely necessary later in the season.

Chemical efficacy varies by species of thrips being treated. If one product does not seem to be working, try a different insecticide. If cotton is treated with a systemic insecticide at planting, it should be scouted for thrips two weeks after plants emerge. If live, immature thrips are found, it means that thrips are laying eggs in the field and residual properties of the seed treatment may have elapsed. Follow-up foliar application may be necessary.

Some of the more popular choices for thrips control in Kansas are the seed treatment thiamethoxam, planting-time applications of acephate and phorate, or foliar treatments of a low rate of dimethoate or acephate.