The western tarnished plant bug (Lygus hesperus Knight) is one of several Lygus species that feeds on cotton terminals, squares, and small bolls. Adults are 1/4-inch-long, have a conspicuous triangle in the center of the back, are winged, and vary in color from pale green to yellowish brown with reddish brown to black markings.
Immature lygus bugs are called nymphs. They are uniformly pale green with red-tipped antennae; late instars have four conspicuous black spots on the thorax and one large black spot near the base of the abdomen. The nymph’s wings are not developed, but nymphs can move rapidly and are difficult to detect in cotton foliage.
Small nymphs may be confused with aphids, cotton fleahoppers and leaf hopper nymphs. Plant bugs prefer legumes to cotton and usually are found in large numbers in areas of alfalfa or potato production or areas providing wild hosts such as clovers, vetches, mustard, and dock.
Lygus bugs are attracted to succulent growth, their feeding results in shedding of squares and small bolls, stunted growth and boll deformation. Feeding damage to small bolls is often characterized as small black spots or small, sunken lesions. The feeding that causes these spots or lesions may or may not penetrate the boll wall and damage developing seeds or lint.
Damage to blooms appears as black anthers and puckered areas in petals.
Management and decision making.
The need for lygus bug control is determined by their abundance in relation to the fruiting condition of the cotton plants. Fields should be inspected for lygus bugs at 4- to 5-day intervals using a drop cloth.
AgFax Weed Solutions
During the first week of squaring, the economic threshold is one lygus bug adult or nymph per 3 feet of row combined with less than 90 percent square set.
In the second week of squaring, the economic threshold is one lygus bug adult or nymph per 3 feet of row combined with less than 85 percent square set. In the third week of squaring, the economic threshold is one lygus bug adult or nymph per 3 feet of row combined with less than 75 percent square set.
After the third week of squaring, the economic threshold is two lygus bug adults or nymphs per 3 feet of row with less than acceptable fruit retention.
After peak bloom, begin treatment when drop cloth counts exceed two lygus bug adults or nymphs per 3 feet of row and plants have failed to retain squares and set bolls normally during the first 4 to 5 weeks of fruiting.
Research in Arizona and California indicates that the western tarnished plant bug (Lygus hesperus) may be more difficult to control with insecticides and may require the use of higher labeled rates of suggested insecticides.