Thanks to the eradication of the boll weevil and the introduction of Bt transgenic cotton, the number of insecticide applications in cotton has been drastically reduced. Prior to these developments, usage of broad spectrum insecticides usually kept stink bug populations in check. While reducing the number of insecticide sprays is a good thing, it has allowed stink bugs to increase to primary pest status.
“Stink bugs are an economic issue in Georgia cotton,” says Michael Toews, University of Georgia (UGA) research entomologist. Although not all fields will require treatment, Toews and UGA Extension entomologist Phillip Roberts suggest that for profit maximization, scouting and treating on an as-needed basis are required. However, many factors need to be weighed in the decision to apply an insecticide.
“Stink bugs are the most common insect we are going to spray,” Roberts says. “The message I continue to convey to producers is to understand what else is in the field, whether it’s spider mites, white flies or small worms. The presence of those insects should factor into the treatment decision when targeting stink bugs.”
But not all stink bugs are the same. In Georgia, the most important species of stink bugs are the southern green and brown stink bugs. Pyrethroids provide good control of southern green stink bugs and are useful when populations of both caterpillar pests and stink bugs infest the same field.
“Brown stink bugs are a little tolerant of pyrethroids,” Toews says. “Organophosphate insecticides need to be added to the mix for brown stink bug outbreaks.”
However, he says, organophosphates increase the risk for secondary pest outbreaks, like spider mites and aphids, and they wipe out beneficials. So, Toews says he went looking for ways to mitigate stink bug infestations without having the negative effects.
Based on research observing stink bug movement, it is well known that stink bug infestations are often first observed near field edges, especially near a peanut planting. Toews conducted studies on spraying field borders, and after four years he recommends spraying field borders as one approach to stink bug management.
“Using a blast sprayer that would reach 30 to 40 feet into the crop, we sprayed four ounces of Bidrin, plus two ounces of Baythroid XL with two applications, one made the first week of bloom and the second application in the second week of bloom,” he says. “Sprays were not made on a threshold.”
Toews says the border sprays appeared to provide about three weeks of protection, and a whole field application was required by week five.
“After four years of research, I can say the trend is that two border sprays tend to buy us about three weeks, then we are generally going to need a full application about the fifth week of bloom. Sometimes that full spray is not needed and sometimes it is,” he says. “I can’t guarantee that two border sprays will work every year, but it is one approach that can be used.”
- Stink bugs move from host crops into field edges.
- Whole field applications are effective, but take time and product.
- The trend is to provide suppression for about three weeks.
- In “light” years, this may be all the treatments that are needed.
- Insecticide savings can be found with border sprays.