Lygus bugs, commonly called tarnished plant bugs in the Southeast, are widely distributed across the Carolinas and Virginia. From a wide variety of hosts, these bugs feed on cotton causing aborted small squares, or worse get into cotton blooms, causing dirty blooms.
Dirty blooms cause poor pollination of cotton bolls. The bottom line is reduced lint.
Lygus bugs are a threat to cotton plants from earliest squaring through cutout and final boll set. Finding an economical and less labor-intensive means of controlling these tiny pest has become more of a challenge in recent years.
The widespread use of Bt-containing cotton seed has reduced the need to spray for bollworms and tobacco budworms. Use of pyrethroids and organophosphate insecticides prior to Bt-cotton kept tarnished plant numbers low.
According to North Carolina State University entomologists, less than 10 percent of cotton acreage in North Carolina was treated for plant bugs in 2005. However, 2006 has proven to be a different story. Though total number of acreages may not increase dramatically, the level of plant bug damage likely will in the upper end of 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.
In the nymph stage these insects resemble adults, but are uniformly pale green with red-tipped antennae. Larger nymphs have five black spots on the upper body surface. Nymphs do not have wings.
Organophosphates or pyrethroids have long been the primary control materials for tarnished plant bugs. Though susceptible to a number of these insecticides, most growers don't consider plant bug damage to be significant enough to warrant treatment.
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.
Insect populations are likely to continue to change in cotton fields across the Southeast because of the increased use of biologicals to control tobacco budworm and bollworm in cotton.
More attention will likely be paid to damage caused by tarnished plant bugs and stink bugs. The North Carolina work implies that non-traditional management techniques, like side-dressing Temik may provide some management options.