Plant Bugs in Cotton

There is a plant complex that we encounter in our fields. Tarnished Plant bug adults are about a quarter of an inch long, have an overall brown color with patches of white, yellow, and reddish-brown, and have a light colored “V” behind the head. The tarnished plant bug nymph is lime green in color with three black dots on its back that, if drawn together, form a triangle; it does not have wings.

Tarnished plant bug adult on a square; note the damage to the square.

Clouded plants bugs look similar to tarnished plant bugs but they are larger. Their color pattern on is different; they are generally brown with patches of yellow, white, reddish-brown, and black on their backs. Also, the first antennal segment is elongated and flared; the antennae also have a striped pattern. The antennae characteristics are also visible in the immatures which are also light green with only one dot on their backs. Identification is important because when you are scouting for tarnished plant bugs and you find clouded plant bugs, they count as 1.5 tarnished plant bugs.

Clouded Plant Bug Adult

Clouded Plant Bug Nymph

Another insect that you will find along with the plant bugs is cotton flea hopper, and they are yellowish-green in color, and have small black dots covering the upper surface. The flea hopper nymphs appear light green or white in color.

Tarnished plant bug has become more common in mid-season problem in recent years because of fewer insecticides are used to control boll weevil, bollworm, and tobacco budworm. Tarnished Plant bugs prefer to feed on squares; small squares that are fed on usually shed from the cotton plant. They will also feed on small bolls that are less than 12 days old. Excessive loss of squares early on can cause for a reduced yield but plant bugs are not the only cause of shed squares – environmental factors will also cause square loss and should be consider a reason for square loss if plant bugs are not present. Larger squares that have been fed on will stay on the plant but the feeding will be evident by discoloration called “dirty blooms.”

According to the Missouri Pest Management Guide: Pre-bloom thresholds are 8 tarnished plant bugs/100 sweeps during the first two weeks of squaring, 15-16 tarnished plant bugs/100 sweeps from the third week until first bloom, and dropping below 80% square retention.

Recent research has shown economic threshold levels for flowering cotton, based on average conditions ($0.65 per pound), were estimated to be between 2.4 and 3.8 tarnished plant bugs per drop cloth sample. When higher prices are considered ($0.85 per pound) thresholds are lower – 1.7 and 3.3 tarnished plant bugs per drop cloth sample. Regions where tarnished plant bug pressure is typically very high, and significant insecticide resistance is likely, it may be beneficial to treat at numbers as low as 2–3 tarnished plant bugs per drop cloth sample. But in areas where tarnished plant bug pressure is low to moderate and insecticide resistance has not evolved, producers may opt to treat at numbers closer to 4 tarnished plant bugs per drop cloth sample.

Other thresholds for flowering control include 15 or more plant bugs per 100 sweeps; 15 plant bugs per 100 plants upon visual inspection or 10% dirty blooms.

Categories: Cotton, Insects, Monitoring, Scouting issues

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