Plant bugs and aphids in cotton

LITTLE ROCK, Ark. — Plant bugs and aphids have always been a concern in cotton production.

The tarnished plant bug is the predominant plant bug in the Delta region. The adult plant bug, a very strong flier, moves around from weed host to cotton field with ease.

Of interest is the plant bug area management program in Arkansas. Extension entomologists are working with USDA to manage movement and wild hosts of plant bugs in large areas. The approach may have some merit, but in the meantime, we must use traditional approaches to manage plant bugs.

So far this year, the constant threat has made insect control more difficult by rainfall and the risk that insecticides will wash off.

Plant bugs damage cotton by feeding on young squares in the terminal, causing the loss of small squares. In most cases, early square loss is due almost entirely to plant bug populations.

Monitoring square set is the most effective way to determine the need for plant bug treatments. The use of shake sheets or sweep nets helps verify the presence of populations. Adult plant bugs, however, are often difficult to sample because they will move before one can use a shake sheet or sweep net. A sweep net is more useful for detecting adults; the shake sheet is more effective for detecting immature plant bugs.

Damage from plant bugs can destroy a cotton crop — almost through the end of summer. I have seen fields at peak bloom completely shut down by plant bugs. High populations — 10 to 20 plant bugs per row foot — can cause plants to shed bolls, squares and blooms.

Using square set or the presence of smallest squares to make decisions on plant bugs is the best plant bug sampling method because you let the plant tell you when treatment is needed.

I try to maintain square set above 85 percent in a cotton field to assure an excellent set of bolls. When peak square is past, square set in no longer the best indicator of plant bug activity.

Aphids are on the increase throughout the Delta. Cotton aphids have several natural enemies, including a parasite and the aphid fungus. Treatment levels are reached quickly because of the tremendous capacity of aphids to multiply.

The aphid fungus does a good job of controlling aphids, but the outbreak does not usually occur until mid-July. Historically, fields with 15 percent infected aphids usually soon have a substantial decline in aphid population levels. If 30 to 90 percent of the aphids are infected with fungus, the population decline is imminent.

Knowledge of fungus occurrence will aid in management of the aphid. The University of Arkansas coordinates a fungus survey. If interested, contact an Arkansas Extension county agent or entomologist.

When plant bugs or aphids reach treatment level, we have an excellent selection of insecticides to choose from.

The older insecticides Bidrin and Orthene give excellent control of plant bugs, especially during peak squaring, but performance may decline later in the summer.

Centric and Trimax also give excellent control of plant bugs and aphids.

The best overall control of aphids is achieved with Intruder — tests have indicated around 98 percent control. Intruder also will give decent control of plant bugs, especially when they are near treatment level.

Donald R. Johnson is a retired Arkansas Extension entomologist who consults on rice and cotton production in Arkansas.

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