We have heard that many folks are considering replanting corn and/or soybean following heavy slug damage this spring. Particularly for corn, we thought it would be prudent to remind folks to pay attention to the various genetic, insect-resistant traits and seed-applied treatments that are available because all that is offered is not always necessary.
For corn seed, recall that you can buy transgenic varieties of corn (often called Bt corn) with various genetic traits that can help protect above- or below-ground portions of plants from some species of insects, including European corn borer and corn rootworm.
For farmers that plant continuous corn, it makes sense to use varieties that have below-ground protection against rootworms; however, if farmers rotate corn with other crops, rootworm control in Pennsylvania is not necessary because rootworms do not occur in first-year corn fields. So it is unwise spend money on rootworm control unless you grow continuous corn!
For above-ground protection, most farmers elect to buy Bt varieties that protect against corn borer. But keep in mind that our research at Penn State has shown that European corn borer populations in most parts of Pennsylvania are at historic lows. Therefore, if you have an understanding of your local European corn borer populations, you can determine the value for your operation of the Bt traits targeting corn borer.
You can help determine the value of these genetic traits to your operation this year by growing some small acreage of untraited corn. If in September this corn has no evidence of corn borer damage, then next year you should be able to save money on seed costs by planting more corn without corn borer protection, but increase this acreage slowly to best understand the risk.
Taking this approach is consistent with IPM because you are deploying a control option when it is necessary, but otherwise are avoiding it and saving the money.
Herbicide Resistance Info
As for insecticides coated on the seeds, our extension team has determined that there can be value in these insecticides when planting into cool soils. Obviously, this time of year soil temperatures are high and seeds should germinate rapidly and start growing quickly; therefore, I would expect to see little benefit for insecticides on corn or soybean seed.
If slugs are your concern, recall that other research that we have done has shown that the insecticidal seed treatment limits predator populations that can help kill slugs. To promote these predators, farmers should diversify their rotations as much as possible (including cover crops) and only use insecticides (including seed-applied, foliar, or soil applied options) when they know a economically significant pest population is present in their fields.
After a few years of these good practices, predator populations should grow to the point where they can really help control slugs and other pests.