Controlling stink bugs in cotton often depends on your knowledge of the ever-changing landscape outside your cotton fields, according to University of Tennessee Extension entomologist Scott Stewart.
For example, did you know that stink bugs prefer a little variety in their diet, with a taste for corn, soybeans, cotton, wheat and wild host plants?
And did you know that they are seed feeders, meaning damage can often be difficult to find? Or that they have benefited from new technologies like Bt cotton and boll weevil eradication?
“We have not had stink bug problems in our crop until the last three or four years,” said Stewart, speaking at the Milan No-Till Field Day. “The primary reason for that is the success of boll weevil eradication.”
Stink bugs are susceptible to insecticides that were used to spray boll weevils. “From the success of boll weevil eradication, Bt cotton and the use of more selective insecticides for plant bugs, we've opened a window for stink bugs.
“Another component of stink bug problems is the impact of changes in the agri-ecosystem in the last five to 10 years,” Stewart said. “It's obvious this year. With good soybean prices, we've seen a lot of early Group 3 and Group 4 soybeans. And they are a good stink bug host.”
Understanding how stink bugs move and behave in the environment can help control the two primary species of concern to Mid-South farmers, the brown and the green, according to Stewart.
“Adults of both species are easily recognizable — the green is green and the brown is brown. They lay masses of 10 to 100, barrel-shaped compact eggs. Identifying the immatures is a little more difficult, noted Stewart.
“It is important to distinguish between the two because brown stink bugs are a little more difficult to control with pyrethroid insecticides. The green stink bug is very easy to control with pyrethroids, Orthene, Bidrin, methyl parathion and Vydate.”
Stink bugs damage cotton by feeding on the seed inside the boll. “Sometimes they will probe several times until they find a seed. Many times, a boll may look fine with only a couple of pock marks. That's the range of stink bug injury. You might see a little bit of stained lint. You might see one or two undeveloped locks. They can totally destroy a boll.”
A drop cloth at several locations in the field is recommended for sampling stink bugs. “In the last three years, we've started looking at injury on thumbsize bolls,” Stewart said. “Be sure to check for internal damage on bolls, because that's a better index of stink bug activity and damage.”
Because they are seed feeders, stink bugs are not likely to be in cotton or soybeans unless seeds are present, Stewart said. “Their hosts include a number of weeds, grasses, cotton, corn and soybeans. They are also strong fliers.”
Stink bug movement from one crop to another can be fairly predictable at times, noted Stewart.
“Early in the year, June 15, I'm going to find stink bugs in Group 3 beans and corn,” Stewart explained. “I'm not going to find many of them in cotton.”
For that reason, cotton producers might consider planting trap crops to “concentrate stink bugs into a known area before they have a chance to build up. Then eliminate them before they get into a more valuable crop like cotton.
“A trap crop doesn't need to be a large percentage of your acreage, according to Stewart. “Another thing to consider, is that if you have a trap crop and you don't treat it, you might actually build stink bugs.”
Stewart is compiling research data on the trap crop system on four area farms. “On each of the farms, we selected four or five cotton fields, and on each side we put four to eight rows of soybeans, usually a combination of Group 3 and Group 4 beans, planted the same day as cotton.
“We want the trap crop to be a small percentage of the acreage, and if necessary, to be a sacrificial lamb for the cotton, which has more value.”
Stewart says the trap crops appear to be working. “In fact, we're starting to treat some of our soybean trap crops for stink bugs. Whether or not this will eliminate the need to spray cotton for stink bugs is going to be hard to determine with one year of testing. We really have to start doing it on a landscape level to see if it's going to work.”
Stewart stopped short of recommending a trap crop this early into the study. “It might be a good idea in some scenarios, and it's not a huge investment. The nice thing about it is that our soybeans are a harvestable trap.
“But if you plant it, you have to manage it appropriately. In fact, you may want to be more aggressive on it than you would a normal soybean crop.”