The short answer to whether you should or should not spray is no for 99 percent of our corn growers.
Stink bug abundances in wheat are even lower than last year. Furthermore, most corn is nowhere near the most “stink bug susceptible” stage (just prior to tasseling).
Most problems with stink bugs in corn come from brown stink bugs moving from wheat into adjacent corn fields days following harvest.
Wheat harvest is beginning and should be in full swing soon. Therefore, my prediction is that there will be fewer problems with stink bugs in corn than we’ve seen in the past.
For a deeper treatment of the subject read on.
Before I talk about corn, I want to point out that you probably won’t want to spray stink bugs in your wheat. Pyrethroid labels carry a 30-day pre-harvest interval restriction for use in wheat. So if you sprayed your wheat now, you couldn’t harvest until July.
Additionally, stink bug densities must be extremely high to cause a yield loss in wheat. I have swept a lot of wheat fields for stink bugs and have never seen yield reducing densities.
Right now, our only effective option for stink bug management in corn is to use ground-applied sprays
Foremost, you should only treat for stink bugs if you reach threshold levels (listed here). These thresholds are based on experimental data and are already conservative. I have a high degree of confidence in them, as a result.
Until V6, the economic threshold is four stink bugs per plant. The most susceptible time for stink bug injury in corn is when the ear is forming, during ear elongation, and during pollen shed. Treat at one stink bug per four plants during these stages.
Economic benefit levels?
Finally, from the end of pollen shed to blister stage, you will see an economic benefit to treating corn if there is one stink bug for every two plants. Stink bugs feeding after blister stage can feed on kernels and have a loose association with increased levels of aflatoxin, but are more of a problem at these stages in southern states, like Georgia and Alabama, than North Carolina.
You might think that tank-mixing an insecticide is cheap insurance, because it will kill any insects in the field and stop you from reaching threshold.
This is untrue for two reasons.
1.) Using a ground rig, at 10 gallons per acre to ensure good coverage, an insecticide will only be effective for one week. After this time, residual is gone and stink bugs can re-invade your corn.
Driving a ground rig over tasseling corn is not an option for most producers due to plant height and/or row spacing restrictions.
2.) Aerial insecticide applications over tasseling corn are ineffective and have no impact on yield. This research was done using large plots in two locations (work published here).
Stink bugs can be killed using ground rigs because the insecticide can penetrate the canopy. Stink bugs often harbor where the leaf collar meets the stalk and in the whorls. Aerial applications at 3-5 gallons per acre dropping insecticide 50 feet above the canopy do not have the penetration power and coverage needed for the job.
Remember that stink bugs are coming off wheat, where the first generation has developed. With mobile stink bugs moving throughout the system and only a week’s control guaranteed with ground applications, stink bugs should not be managed using an “automatic spray”.
To be effective, you should only treat stink bugs if the threshold has been reached and if you can use a ground rig.
Focus on high volume and pressure applications to penetrate the canopy and only expect about a week of control.
Finally, remember that Orthene and Bidrin are not registered insecticides in corn.
If you do decide to treat stink bugs by air, focus on the edge of corn near wheat. Stink bugs stack up on the single row of corn adjacent to wheat. Be sure you treat corn before tasseling.
Finally, try to work with your aerial applicator to do anything you can to increase penetration of the insecticide into the canopy.