Stink bugs emerge as major pests

Cotton insect control changing Amid the recent technological advances in cotton insect control, some pests, including stink bugs, have fallen through the cracks.

"In many areas of the Cotton Belt, successful eradication of the boll weevil, expanding use of transgenic Bt cotton and advances in lepidopteran-specific insecticide chemistry all have contributed to our changing pest complex in cotton," said Jeremy Greene, University of Georgia entomologist, speaking at the 2000 Georgia Cotton Production Workshop held recently in Savannah.

As a result of these changes, growers have reduced their use of broad-spectrum insecticides, allowing stink bugs to avoid a "coincidental demise," says Greene.

Three species found Three species of stink bugs are found in Southeastern cotton, notes the entomologist, and they include the green stink bug, the Southern green stink bug and the brown stink bug.

"Organophosphorus insecticides such as dicrotophos (Bidrin) and methyl parathion provide excellent control of stink bugs in cotton," says Greene. "Pyrethroid insecticides also will offer control - apparently differing between species - and are useful when populations of lepidopterous pests and stink bugs are present concurrently."

The choice of an insecticide, he says, will depend on the cotton variety, insect pressure and species of stink bug present in the field.

For growers to understand how to better manage stink bugs, they must have an understanding of the biology of the pest and how they relate to their environment, he adds.

"We should strive to know what stink bugs are capable of and not capable of, what their weaknesses and strengths are, and how their surroundings and our manipulations can affect them," he says.

As stink bugs age, he explains, they can cause increasing damage to bolls in terms of visible symptoms of feeding and yield loss.

"Late instars - the fourth and fifth - of the Southern green stink bug can cause damage comparable to that caused by adults. Also, we've found that bolls younger than three weeks from white bloom remain susceptible to damage from stink bugs but decrease in susceptibility with age," notes Greene.

Many states, he says, have adopted the same treatment recommendations for stink bugs in cotton, with minor variations. "Insecticide application is recommended at one bug per six feet or row. Because bugs frequently are difficult to detect, some states now recommend a threshold for treatment based on a percentage of bolls - from 10 to 20 percent - internally damaged by stink bugs.

"In Georgia, we recommend intervention with an insecticide at the one bug per six feet threshold and/or when 20 percent of medium-sizes bolls have at least one internal feeding symptom per boll. These symptoms include wart-like growths or stained lint/seed associated with puncture."

Traditional methods of monitoring for stink bugs include using a drop cloth or a sweep net and examining bolls for feeding symptoms, says Greene. The drop or ground cloth probably is the best method, he says, but cotton must be at least waist-high, and there's the potential of scaring the stink bugs.

"Trapping stink bugs in pheromone traps also has potential as a monitoring tool for stink bugs in cotton. Stink bugs can be caught successfully using the combination of a commercially available lure for the brown stink bug complex and a trap designed to visually attract stink bugs.

Effectiveness hindered "However, the effectiveness of the trap currently is hindered by the unavailability of effective lures for other species, such as green and Southern stink bugs. Trap capture could have some predictive value in terms of population development in the crop. However, additional research in this area is necessary."

Greene advises growers to use appropriate scouting procedures, the latest threshold recommendations, proper insecticides and a timely management system to adapt to the ever-changing pest complex in cotton.

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