Tarnished plant bugs take bite out of cotton

Prior to the introduction of Bt-gene containing cotton seed, tobacco budworms and bollworms were managed with an array of insecticides. As a sidelight to these yield-damaging worms, the insecticide regimen routinely controlled plant bugs.

Now that bollworm and budworm sprays have been dramatically reduced, plant bugs have increased as a problem throughout the Cotton Belt.

Tarnished plant bugs, technically Lygus bugs, in the adult stage are about one-fourth inch long and one-tenth inch wide, and flattened on the back. They vary in color from pale green to yellowish brown with reddish brown to black markings, and have a conspicuous triangle in the center of the back.

Left unmanaged, tarnished plant bugs can create some problems for cotton growers. Lygus bugs pierce squares and damage anthers and other tissues. When squares are less than one-tenth inch long, they shrivel, turn brown, and drop from the plant.

Damage to larger squares may interfere with fertilization. If many squares drop, the plant may put its energy resources into vegetative growth, resulting in tall, spindly plants and reduced yields.

Since conventional treatment with insecticides may require several sprays, over a long period of time from pre-plant to near harvest, entomologists at North Carolina State University set out to find some alternative ways to control these pests.

Eric Blinka, a graduate student in entomology at North Carolina State, applied Temik in a side-dress application to control tarnished plant bugs. When cotton reached the match-head square growth stage he applied five pounds of Temik. After a week, he collected lygus bug nymphs, put the insects into mesh sleeves and placed them on cotton plants. He allowed these insects to feed on the plant for seven days.

He duplicated the tests with 10 pounds of Temik per acre. The labeled rate for Temik on cotton at match-head square is 14-17 pounds per acre.

After determining the number of lygus bugs remaining alive in the cages, he put the cages back on cotton plants. He did this four times in 2006 to determine the residual effect of Temik on lygus bugs.

Based on these tests, Blinka says it appears Temik even at the low five pounds per acre rate, applied as a side-dress at the match-head square stage in cotton, will provide 3-4 weeks of lygus bug control.

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