Like clockwork, during the last week of May and first week of June, calls start coming in about stink bugs in corn.
Very few of these calls are generated from growers or scouts finding stink bugs in corn at significant levels. The majority have been generated at the chemical dealer level, recommending a tank-mix of an insecticide and a fungicide.
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. Most of our corn has passed this stage and stink bugs generally are not in corn until V6 anyway.
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.
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 more 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.
The major stink bug species in corn, far and away, is the brown stink bug. Like the situation in cotton and soybeans, you might be able to kill 60-70 percent of them with a pyrethroid. This will only be the case if you treat by ground.
Remember that stink bugs are coming off of wheat, where the first generation has developed. This migration is beginning to happen now and will continue to take place over the next several weeks.
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”.
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.