Stink Bugs Bring Late-Season Fireworks

After viewing the July 4th fireworks, cotton growers in the Southeast start watching for something a lot less enjoyable – stink bugs damaging cotton bolls.

This year, some growers will be taking a look at a new “dynamic” economic threshold strategy for stink bugs. Cooperative Extension entomologists have evaluated the system during four years of field trials and now believe it is ready for farms, says North Carolina State University Extension entomologist Dr. Jack Bacheler, a leader in developing the dynamic threshold concept.

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“The Southeast had dry conditions and light stink bug pressure the last two years,” says Bacheler. “But this year we’ve had much more moisture, and that usually is good for stink bugs.”

Careful, consistent scouting will work in tandem with the new dynamic thresholds for treatment of stink bugs, he says.

Other Extension entomologists working on dynamic thresholds include Dr. Philip Roberts, University of Georgia; Dr. Jeremy Greene, Clemson University, and Dr. Ron Smith, Auburn University. From 2005 to 2008, 80 trials were held across the Carolinas, Alabama and Georgia to help develop the thresholds. Much of the work was funded through Cotton Incorporated and regional state support committees.

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“We found that there was hardly any yield reduction when controlling stink bugs during the first two weeks of bloom, but there was a good return when spraying during weeks three, four and five of bloom,” says Bacheler. “Once the crop has proceeded beyond weeks five or six, the bolls are bigger and less susceptible to stink bugs, so we could raise the thresholds accordingly.”

In the traditional “static” threshold, spraying would start when 20% of bolls sampled show internal damage from stink bug feeding. Typically fields are scouted starting the first week when a substantial amount of the plants have white blooms. Bolls the diameter of a quarter are opened to look for stink bug feeding signs, such as stained lint, warty growth and boll rot.

During early bloom when no bolls have reached the diameter of a quarter, scouts should sample the largest bolls present and monitor boll retention. Stink bug feeding on small bolls of less than a week old may cause the bolls to shed.

“By the third week of bloom, the first available bolls are 15 days old and at the size and tenderness stink bugs like,” says Greene. “Serious scouting is then needed every 5 to 7 days until the last bolls are too hardened for stink bugs to penetrate. During weeks three, four and five of bloom, we have the largest proportion of susceptible bolls to protect, and the threshold should drop to 10% of sampled bolls penetrated. Scouting and spraying should be more aggressive.”

When it’s time to spray, proven control products are available, and several are off patent and value priced.

Lambda-cyhalothrin, the active ingredient in MANA Silencer 1EC, provides fast knock-down for those key weeks when bolls are most vulnerable, and the bifenthrin in Fanfare 2EC is excellent for mite control as well as stink bugs,” says Dr. Duane Martin, MANA manager of new business and product development. “MANA Acephate 90 PRILL is an organophosphate formulation convenient to work with, and it also provides control of thrips, whiteflies and plant bugs.

“All those active ingredients are on recommended lists of the Southeast Extension bulletins. A couple of states also include Diamond 0.83 EC with the insect growth regulator novaluron targeting nymph stages,” he adds.

Organophosphates, such as acephate, Bidrin and methyl parathion, will control brown stink bugs, which are less susceptible to pyrethroids. Both organophosphates and pyrethroids are effective on the green stink bug, dominant in some areas.

Editor’s note: Some information for this story was provided by MANA.

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