Stink bug damage in cotton has increased throughout the Southeast in recent years, going from less than 0.1 percent damage in 1992 to an estimated 200,000 bales lost Beltwide in 2005. Though not a new pest to cotton, changes in cotton production have elevated this pest to a new level in recent years.
Speaking at the recent Beltwide Cotton Conference in San Antonio, Texas, University of Georgia Entomologist Phillip Roberts says this change in status of stinkbugs is due to overall reduced use of broad spectrum insecticides. In the past, he explains, stinkbugs were kept in check by insecticides targeted primarily for other insect pests of cotton.
The Boll Weevil Eradication Program, extensive use of BT cotton, and increased availability of selective insecticides, have all contributed to reduced incidental control of stinkbugs, according to Roberts.
Over 200 species of plants are host to stinkbugs, which can go from egg stage to adults in 30 days. In the Southeast, there is a particularly good host, peanuts, which are commonly grown in fields adjacent to cotton. Roberts points out that managing these high risk areas is one strategy for overall reduction of stinkbug damage.
In cotton, stinkbugs feed primarily on the boll. These insects cause extensive damage to the seed, but perhaps more importantly, Roberts stresses, stinkbugs may open the cotton boll up to other pathogens via plant wounds, or even introduce new pathogens during feeding.
Stinkbug damage in cotton may manifest itself in several ways, according to Roberts. In some cases the boll may open and fluff normally, or bolls may fail to fluff and show extensive localized staining, or in worst case scenarios the entire boll may rot and fall off the stalk.
Perhaps the biggest risk to cotton is in reduced quality, according to Roberts. Unfortunately, he points out, much of cotton damaged by stinkbugs is harvested. “In every test in which we controlled stinkbugs, fiber length was increased,” Roberts says.
“In 2004, cotton from the most heavily infested test fields showed a bale per acre loss in yield,” Roberts continues. “We also saw significant reductions in lint fracture, staple length and color grade losses, constituting about a $9 per bale loss in quality,” he explains.
Control of stinkbugs is relatively easy, Roberts contends. The problem is knowing if and when to spray. Scouting is critical to management of these pests, he says. Scouting should be started when bolls are present.
Quantifying stained lint and internal warts on the bolls, which are internal signs of bug feeding is critical to managing stinkbugs, Roberts stresses. Drop clothes, sweep nets and physically scouting plants are needed to determine level of insect infestations and type of stinkbug present in the field.
Organophosphate insecticides are effective on brown stinkbugs, and both organophosphates and pyrethroids provide excellent control of Southern green and green stinkbugs. When selecting an insecticide for use on stinkbugs, growers should be aware of bollworms and armyworms which are likely to be in the field and adjust spray treatments to account for these pests.
Managing stinkbugs, Roberts concludes, can add both yield and quality to a cotton crop in the Southeast.