Stink bug outlook unpredictable

For cotton growers, stink bugs present a frustrating problem: Although many cotton insects and their damage vary from year to year and from field to field, stink bugs probably take the cake.

With pests like plant bugs and cotton aphids, at least North Carolina cotton producers know that treated acreage averaged over the state will usually vary from 2 percent to 10 percent. No such luck with stink bugs.

In 2004, “The Year of the Stink Bug” in North Carolina, two to three applications for this pest group would have paid off for most producers, while in 2002, 2003 and in 2007 probably 80 percent to 90 percent of our cotton fields did not need a single treatment for stink bugs. With this huge variation in possible stink bug damage, one can quickly realize the importance of scouting as opposed to a calendar approach.

Looking back, 2004 seemed like the beginning of a rough period for stink bug damage. In hindsight, 2004 was close to a perfect storm of a mild winter, no late frosts, and plentiful rainfall over most of the state that served to increase both the growth of the many wild and cultivated hosts of green and brown stink bugs as well as the attractiveness and susceptibility of cotton to stink bugs.

And although 2007 and 2008 appear to suggest a downward trend in damage, at this point in the growing season we are almost as likely to get another 2004 “bug year” as another 2007.

Generally, expect higher levels of stink bugs if our 2009 trend of wet weather continues through July. Irrespective of stink bug levels, we are now in a far better position to manage these pests than was the case in 2004, thanks to a Southeastern multi-state effort that shed significant light on how deal with these pests.

Entomologists from Virginia, North Carolina, South Carolina and Georgia participated in the first Cotton Incorporated-sponsored regional project from 2005 to 2007 entitled: “Identifying Practical Knowledge and Solutions For Managing The Sucking-Bug Complex In Cotton: Research in the Southeast Region” Several aspects of this work have continued into 2008. Some of the practical results of this project follow.

• Plant bugs vs. stink bugs: Stink bugs are far more of an economic threat to profitable cotton production than plant bugs in the Southeast.

• Stink bug species: Although green stink bugs are more prevalent in North Carolina and Virginia, southern green stink bugs are more common in Georgia, and brown stink bugs are common to all areas. Management approaches for this complex were found to be similar.

• Maximum vulnerability to damage: The third though fifth weeks of bloom was found to be most susceptible period for economic injury from stink bugs.

• Dynamic threshold: Of the various internal boll damage symptom thresholds evaluated (seasonal static thresholds of 10 percent, 20 percent, and 30 percent and a dynamic threshold of 50 percent, 30 percent, 10 percent, 10 percent, 10 percent, 30 percent, 30 and 50 percent that changed by week of bloom), insecticide applications based on use of the dynamic threshold resulted in the highest net returns under various stink bug population levels.

• Impact on fiber quality: Poorly managed, stink bugs can reduce fiber quality, but no HVI and APHIS cotton fiber quality parameters were adversely impacted when thresholds were correctly applied.

Additionally, the following findings show potential for further refining stink bug management:

• External boll damage: Scouting assessments of external stink bug boll damage feeding symptoms show promise as a means of increasing scouting efficiency by either reducing the time in evaluating bolls, or by being employed as a rapid indicator of whether further internal boll damage assessments are indicated (a “hybrid” approach).

• Stink bug movement into cotton fields: Studies of stink bug movement into cotton field edges shows promise as both a possible early indication of stink bug establishment and as a possible perimeter spray treatment approach.

Cotton scouts should pay particular attention to weeks 3 to 5 or 6 of the bloom period, a time of maximum cotton crop susceptibility to economic boll damage from stink bugs. The dynamic threshold approach provides better economic returns than both our past 10 percent and other states’ 20 percent internal boll damage threshold under low, medium and high stink bug levels. For North Carolina cotton producers, we recommend that they follow a threshold of 50 percent, 30 percent, 10 percent, 10 percent, 10 percent, 30 percent, and 30 percent or 50 percent internally damaged bolls by week of bloom. This approach should help maximize cotton producers’ return on investment by limiting sprays to the time of greatest need.

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