Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu
As wheat matures and is harvested, watch for stink bugs moving into adjacent corn fields. Brown stink bugs are the most common species found in wheat in Delaware. Corn is most sensitive to stink bug feeding injury when infestations occur during earlier plant growth stages (late vegetative-tasseling) compared to later growth stages (pollen shed-grain fill). Based on recommendations from NC State, the threshold for stink bugs in corn is one stink bug per four plants when the ear is forming, during ear elongation and beginning of pollen shed; and one stink bug per two plants after pollen shed (these thresholds have not been evaluated in Delaware).
Begin scouting corn fields for stink bugs, especially those fields adjacent to wheat and fields bordered by weedy ditches. The greatest yield loss potential from stink bug feeding occurs prior to pollination, so waiting until tasseling may be too late. A paper recently published by Dr. Dominic Reisig, NC State Associate Professor and Extension Specialist, has determined that getting control of stink bugs is difficult once tasseling occurs. This is due to the dense foliage above the ear zone and the habit of stink bugs to seek refuge in leaf axils and in the folds of leaves. Also, if you are planning on including an insecticide with your fungicide application at tasseling to target stink bugs, it will likely be too late because most of the damage is already done.
Here is an excerpt from a newsletter published by Dr. Dominic Reisig, NC State Associate Professor and Extension Specialist, discussing his results evaluating aerially applied pyrethroid applications to manage brown stink bugs in corn:
“Stink bugs are difficult to kill with aerial applications because the insects can hide in leaf folds near the stalk. Make it clear to your aerial applicator that you want to penetrate the canopy and kill insects. There are aerial applicators that can kill stink bugs based on follow ups we’ve made in the field after sprays. Stink bugs can be killed for up to a week using a high-clearance tractor (see screening information graph). Don’t expect much, if any, residual from your chemical. Stink bugs can reinvade the field after sprays.”
Here is a link to the full article: https://entomology.ces.ncsu.edu/2017/06/manage-stink-bugs-in-corn-before-it-tassels/?src=rss
Here is a link to the publication: http://www.bioone.org/doi/pdf/10.1673/031.011.16801
What about including an insecticide with fungicide applications at tasseling? This approach has not been shown to be effective at reducing stink bug infestations and preventing injury to corn from stink bugs for several reasons:
- Stink bug injury on corn is more severe when feeding occurs during earlier growth stages (prior to pollen shed).
- Most of the yield limiting damage to developing corn ears has already occurred.
- Controlling stink bugs in corn after tasseling is difficult.
- These two timings do not overlap.
This year, wheat appears to be maturing ahead of schedule and many of our corn fields are slightly behind in development. With this in mind, I expect brown stink bugs to move from wheat and other host plants and into corn when many fields are at the most vulnerable stage. If stink bugs are moving from wheat into adjacent corn fields, consider spot treating before they disperse throughout the entire field.
If you need to spray your corn for stink bugs, most pyrethroids should provide control. However, based on a vial bioassay conducted in NC using brown stink bugs collected from wheat, bifenthrin was found to be the most efficacious.
Here is a link to the report: https://entomology.ces.ncsu.edu/2017/06/insecticide-choice-for-stink-bugs-in-corn/?src=rss
If you have high stink bug populations in your wheat fields that are in proximity to corn, can you control the stink bugs in the wheat before they move to the corn? There hasn’t been any research to answer this question. However, given the pre-harvest intervals of most of the materials labeled in wheat that will provide stink bug control and their short residual activity on stink bugs, it is unlikely that an application will be successful in preventing populations from building in the wheat.