Early season cotton insects can steal yield

Considering the investment already in the ground, early season insects — while at times considered a relatively minor pest of cotton — are not to be taken for granted.

Research continues to show yield advantages when producers are diligent about controlling insect pests early in the year.

Unless cotton producers were late planting this year, most of them should be beyond the thrips window by about mid-June, says Ron Smith, Auburn University Extension entomologist. “We’re catching an astronomical number of thrips right now,” said Smith in late-May. “But it could all be over in a period of just a couple of weeks, and later planted cotton likely will grow out of them.”

Grasshoppers also have emerged as a pest of seedling cotton in recent years, says Smith, primarily in conservation-tillage systems. They chew the main stem of young plants, causing a reduction in stands.

“Cotton is most susceptible to grasshopper injury from the time it begins to emerge in the ‘crook stage’ until the plants have about six true leaves. Both the immature and the adult stages may cause injury. Controls are needed whenever stands are threatened,” he says.

Thrips will attack all cotton fields each year and are capable of causing significant injury, say AU Extension entomologists Tim Reed and Barry Freeman. As a result, virtually every field in the state receives a preventative treatment for thrips either as a seed treatment or an in-furrow granular insecticide application.

“Nevertheless, under poor growing conditions, an additional foliar application is sometimes required. To receive the most benefit, the foliar application should be made early — generally between the first and second true leaf stage. It is most unusual for cotton with four or five true leaves to profit from foliar sprays. Numerous inexpensive options are available for foliar thrips control, but these sprays can contribute to the flaring of other pests such as cotton aphids and spider mites,” report the entomologists.

Once growers are past the thrips window, it’s time for them to turn their focus to plant bugs and aphids, says Smith. “There’s no way of knowing if we’re going to have a heavy or ligher-than-normal plant bug year,” he says. “Fleahoppers were heavy this year in the Coastal Bend area of Texas, so that’s something to be aware of.”

Plant bugs should become a concern to growers whenever pinhead square retention is significantly below 80 percent, says Smith. “If you’re scouting cotton, you can see the pinhead square retention in the field, and it’s important to keep it above 80 percent. By about mid-June, we’re seeing mostly adults. You can also check plants by shaking terminals over a sweep net or drop cloth prior to first bloom,” he says.

Plant bugs migrate to cotton from weeds and various legumes. In pre-bloom cotton, both adults and nymphs feed on tiny squares, causing them to turn black. These insects are usually found in terminals and move quickly about the plant or fly when disturbed.

Auburn University recommendations call for making one or more applications when 100 adults and/or nymphs are found per 100 row feet. If early square set is less than 80 percent, make one or more applications when populations exceed 50 adults and/or nymphs per 100 row feet.

Sampling techniques are not adequate when the majority of the plant bug population is in the adult stage.

Plant bugs can also be a problem in blooming cotton (July-August). At this point of the season, a large portion of the plant bug population is nymphs, and large squares and young bolls are damaged in addition to the small squares.

Plant bug damage to young bolls results in “hard-locking” of one or more locks per boll. Damage to large squares is revealed as “dirty blooms,” which show necrotic flower parts and warty petals caused when the bugs feed on large squares.

Controlling plant bugs in blooming cotton generally is warranted when 15 to 20 percent of bolls the diameter of a quarter reveal internal plant bug damage.

Aphids also can become a problem by about mid-June before crashing sometime in July due to a naturally occurring fungus, notes Smith.

“They always seem to crash later than we want them to,” he says. “

Aphids may be numerous in cotton fields at any time during the growing season. They are usually found on the underside of leaves, on stems, and on terminals. Curling and yellowing of leaves indicate infestation.

At-planting insecticides may help in controlling aphids early in the season. Additional control measures are recommended when honeydew production is heavy.

While there might be a lull from early to mid-June in terms of cotton insects, growers should be aware that there are usually some erratic pests in the mix, such as false chinch bugs, which have been reported in Georgia, says Smith.

The false chinch bug (FCB) will suck juices from the plant and cause it to wilt. Close scouting will help ascertain the level of FCB damage and help determine if control measures are justified. FCB is very difficult to control with chemicals and is often found in association with common groundsel, cutleaf evening primrose and other winter weeds.

In addition, producers who are growing conventional cotton this year could see some bollworm damage by as early as mid-June, he says. “Growers of conventional cotton, of which we have a few in east-central Alabama, should not get into an early battle with bollworms,” says Smith.

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TAGS: Cotton
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