Cotton in most areas of the Upper Southeast is ahead of the five-year schedule of growth for mid-July and is at or nearing its most vulnerable stage for stink bug damage.
North Carolina State University Entomologist Jack Bacheler says, “Weeks 3 through 5 of the bloom period is the time interval when the levels of stink bug-susceptible bolls are at their highest. This is also the time when a 10 percent damage threshold should be used.”
He adds, “Remember that our goal is to reduce or eliminate an economically-damaging population of stink bugs, not to ineffectively try to reverse boll damage that’s already taken place.
Clemson University Entomologist Jeremy Greene says there are a couple of good ways to check for stink bug infestations. The key to both is to start scouting for stink bugs when small bolls appear.
The first method is to randomly select at least 25 bolls that are at least one inch in diameter per field and add one additional boll for each acre exceeding 25 acres, he says.
Each boll should be broken open and the carpal walls, lint and seed should be examined for injury symptoms, including warty growths on the carpal wall and discolored lint and seed, Greene says.
Growers can also rate an infestation based on numbers of stink bugs by using a beat cloth or beat pan. Carefully approach and shake the plants on at least 30 total feet of row from 10 three-foot samples. When going by numbers of stink bugs, one or more stink bugs per 6 feet of row indicates the need for an insecticide.
Choosing an insecticide
Typically, growers who use a pyrethroid-based insecticide for bollworm control will be able to control green stink bugs and Southern green stink bugs. If the infestation is dominated by brown stink bugs, Bidrin or methyl parathion should be used, Greene says.
“Be especially vigilant for stink bugs in both Bt cotton and non-Bt cotton fields when no treatments are being applied for caterpillars,” he warns.
Bacheler says in North Carolina, “Based on calls and our own observations, we appear to have moderate to high levels of stink bugs in many areas of the state, with a few fields in the mid-20 percent boll damage level.
“Fortunately, up to this point many cotton fields are in the single digits for damage, though this could change as more stink bugs invade cotton fields and additional fields enter the third week of bloom when the 10 percent threshold is in effect.”
Ames Herbert, Virginia Tech entomologist and IPM leader says, “Most of our cotton is about 10 days to 2 weeks into the blooming period. This is the perfect time to begin scouting for stink bug damaged bolls.
“We just completed 5 cotton field scouting clinics across our cotton region and it was not hard to find stink bug damaged bolls, and a couple of fields had high levels (30-40 percent) of internal stink bug damage,” he adds.
All three entomologists urge cotton growers to use the new cotton stink bug scouting cards, which provide the thresholds, scouting procedures and a template for determining the proper size of the bolls that should be used to make any treatment decision.
These cards can be obtained from county or regional extension agents.