Check Wheat and Corn for Stink Bugs- Management Recommendations
Stink bugs this year have been a persistent problem in corn, especially in the east. Now is the time of year when adults can really show up in corn, as they have developed a generation in weeds and wheat. I have a student, Arun Babu, who is sampling wheat and corn across Eastern NC. He has found that about 10% of the corn fields or 10% of the wheat fields he is sampling have high densities of stink bugs. Below are my recommendations to avert problems in corn:
Is unharvested wheat adjacent to your corn?
Yes. Best sampling method in wheat is the sweep net. If you capture 5 or more stink bugs in 20 sweeps (swooshes of the net), be vigilant for movement into corn (look below for what you should do in corn). Ignore rice stink bug since they are not a pest of corn. Keep in mind that stink bugs are very very rarely economic problems in wheat (see previous article) and that all registered insecticides have preharvest interval restrictions that limit their use.
If you do not have a sweep net, use your best judgement for how many stink bugs you normally see in wheat this time of year. Ignore rice stink bug since they are not a pest of corn. If it seems like there are a lot of brown stink bugs, be vigilant for movement into corn (look below for what you should do in corn).
You also need to check corn next to unharvested wheat. If you decide to treat before wheat is harvested, realize that stink bugs will likely move in from wheat after harvest into your corn.
No. Check weeds and forested areas near your corn, especially if you have weedy ditches nearby. These often provide holding places for stink bugs that can move in and out of fields. Always a good idea to check the corn, as well, just to be sure.
Is harvested wheat adjacent to your corn?
If so, you should check corn for stink bugs. Count stink bugs directly on the plant, searching from the bottom up and in leaf folds. The best time to treat is 5-7 days after wheat harvest. This is the sweet spot where stink bugs should have moved over from the harvested corn, but might not spread throughout the field.
How and when should I treat corn?
Thresholds, based on GA data are 25% infested plants (prior to tasseling), 50% infested plants at tasseling, and 100% infested plants at the milk stage. Just to be protective, I am willing to move the threshold to 10% infested plant prior to tasseling, since we seem to have most our problems as the ear is pushing out.
However, I would urge you to avoid unneeded sprays unless you hit threshold at tasseling and later. Published recent research from NC has demonstrated that airplane sprays made at this stage (generally tank mixed with an insecticide) are not effective to kill stink bugs. Think about it. Stink bugs can hide at the base of plants, in leaf folds, and on the ear. Will a 3 GPA aerial insecticide really penetrate the canopy and kill stink bugs?
If you need to spray, focus on delivery of the insecticide to the insect. A high-boy is preferable to aerial application, but if you must treat by air, have the applicator up the volume and focus on coverage. Also, consider air induction nozzles at lower volumes. Brown stink bug is susceptible to most pyrethroids and organophosphates. Don’t expect much, if any, residual from your chemical. Stink bugs can quickly reinvade the field after sprays.