A violet ground beetle eating a slug

A violet ground beetle eating a slug

Pesticides can wipe out insects that can in turn wipe out a field of corn in a matter of days.

A farmer who sees a handful of black cutworm moths flying around in newly planted corn might be tempted to call in a custom sprayer to get rid of the pests before they lay waste to the crop.

That kind of knee-jerk reaction is not the best way to deal with pest problems. Penn State entomologists Anna Busch and John Tooker talked during a recent Extension webinar about how to deal with slugs and insect pests in no-till corn.

Sometimes the best defense is to let Mother Nature deal with a minor problem before it becomes a major problem, Busch told her virtual audience of about 50 farmers, crop consultants, crop scouts, commercial applicators and industry reps.

The webinar was a review of and updates to the principles of integrated pest management techniques. The IPM philosophy allows insect pests and slugs to munch away on young corn plants, but only up to a point, according to Busch.

Insecticides are the last resort for pests in no-till corn, she said. A spray is called for only when the economic loss of crop damage looks like it’s going to exceed the cost of an insecticide application. The only way to figure that out, she said, is to know what’s in the field. Scouting is the best way to do that.

Busch means boots on the ground, knees in the dirt, eyes on the developing plants, looking closely for signs of trouble.

“You can’t scout a field by driving past it at 55 miles an hour,” she said. “If you don’t have time to scout yourself, you can find people to do it for you.” Crop scouts who visit every other week or so during the early part of the growing season might work for $7 an acre she said. Accurate scouting reports can help growers decide whether to spray, preserving yield if they do, and avoiding a significant expense if there’s not enough damage to warrant the cost of spraying.

Spraying just for the sake of spraying — just to be sure — can be a mistake both economically and environmentally. Insecticides don’t just kill their targeted species, they also kill the predators that feed on the targeted species.

It is possible to grow no-till corn with no insecticides. Drew Haines, for example, won the 2019 National Corn Yield Contest. Haines, along with his brother and son, farms 600 acres of non-irrigated, no-till corn in Middletown, Maryland. The Haines family yield last year was 422.352 bushels to the acre.

Haines reported that they had used no insecticides on their corn ground for the last five years.

A lot more than insect pest control goes into a 422-bushel yield, of course, but Busch said predators, natural enemies of crop pests, “can make a big difference, but we really need to give them a chance, and to farm with them in mind.”

When scouting for crop damage, Busch said it’s important to scout for predators as well. Most predatory species will have their heads facing forward, they’ll be scurrying about and they’ll be most active at night. It’s best to scout for predators early in the morning or evening.

Ground beetles, soldier beetles, lightning bugs and wolf spiders are all important predators. Ants can be predators, but they can also be farming aphids that can cut into yields.

Bt (Bacillus thuringiensis) corn varieties can also be a big help in combating insect pests, according to Tooker. But before the seed goes into the ground, the grower needs to know which genetically engineered Bt variety will help reduce the harmful insect populations for their particular fields. There is a publication, “The Handy Bt Trait Table,” that helps match seed variety with bugs that need to be dealt with. It is updated every year and is available from many seed reps. The 2020 edition is also online at bit.ly/3i5hqbn

Tooker is a proponent of the no-till-cover-crop-diverse-rotation school of crop production.

“If you want to use natural enemies as part of your pest control program,” he told his virtual audience, “you need to farm with them in mind. One of the best ways to do that is to stick with no-till, or adopt it if you haven’t already done so.”

No-till is a basic conservation practice, Tooker said, and there are more natural enemies in no-till fields. Adding cover crops to the mix encourages even more natural enemies. Adding a diverse rotation program will help predators even more to eat the invaders that are feasting on your crops.

“But even if you’re doing those three things,” Tooker said, “you can’t forget about the total IPM approach.”

Integrated pest management, Tooker made clear, is the fourth leg in controlling economic loss from insect pests. IPM helps growers decide when an insecticide spray is necessary, where it’s necessary, how much is necessary and the cost of materials versus the cost of potential crop losses if a spray isn’t applied.

The insect and planting green issues covered in this brief recap were part of a Penn State Extension agronomy field day which aired on Aug. 14. The full webinar can be viewed online at bit.ly/3bAmDFM


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