Changes Bring New Pests

May 15, 2009 02:18 PM

Planting the best-yielding hybrid and modifying your management practices can bump yield. But failing to adjust pest management to reflect changing conditions in your fields could cost you that increased yield and more, says Bill Bauer, who operates B & M Crop Consulting in Coldwater, Mich.

For example, tests by Farm Journal Field Agronomist Ken Ferrie indicate that narrowing your corn row width may
increase yield by 7 bu. to 10 bu. per acre, from improved moisture management. But reduced air circulation in the denser plant stand increases the likelihood of Northern leaf blight or common rust, even if you haven't been troubled by those diseases in wider rows. "Those diseases could cause you to lose 10 bu. to 15 bu. per acre, negating the benefit of narrow rows,” Bauer says.

Thinking through the effect of new production practices on insects and diseases can prevent situations like that. At the 2008 Farm Journal Corn College, Bauer explained how to turn your pest management from reactive to proactive so you can spot pests in time to minimize damage.

Any change you make also changes the environment for pests. "Narrow rows and higher population reduces air circulation in the crop canopy, which can lead to more disease,” Bauer says. "So as you narrow your row width, you need to think about applying fungicides.”

Bugs in half a field.
Tests at the Corn College site and elsewhere show how one change can affect a pest. "Where corn was planted conventionally and with no-till in the same field, we had cutworm pressure in the no-till but not in the conventional—right up to the line,” Bauer says.

"Among my own clients, one 2,000-acre no-till corn grower had 400 acres of corn where he was unable to spray for winter annuals in the fall or apply a burndown herbicide in the spring,” Bauer adds. "As he planted, weeds were growing in the unsprayed fields.

"Because that grower was scouting proactively, he was able to rescue those 400 acres from cutworm damage. If you don't find cutworms until corn is in the V6 stage, your stand could be reduced from 32,000 plants per acre to 20,000, and it's too late to do anything about it.”

A proactive approach to cutworms requires taking stand counts at the V2 stage. "If you find 3% to 5% of plants showing damage, you can apply an insecticide treatment and save the crop,” Bauer says.

Proactive pest management goes on all year long. "Start by learning about the common pests in your area,” Bauer advises. "Know whether they overwinter in soil, in crop residue or are blown in on southerly winds. If a pest overwinters in crop residue, take that into account if you switch from tillage to no-till planting in order to save fuel.”

Off-season homework. Learn everything you can about the genetic strengths and weaknesses of your hybrids. "Some hybrids have more natural resistance to corn borers than others,” Bauer says. "Some can regenerate roots faster, so they can tolerate a little more rootworm feeding, depending on the area and insect pressure. Some are more susceptible to aphids because of the way they grow and the sugars they produce.

"New hybrids come out so fast it's hard to keep up with them. Glean as much information as you can from your seed company. Then network with other farmers.”

If you anticipate heavy insect pressure, plant genetically modified resistant hybrids. "When selecting hybrids, make sure you understand the insect and disease ratings used by each company because there is no uniform standard,” Bauer cautions.

Growers should record which hybrids are planted in each field—even though that can be difficult during a fast-moving planting season. "If you forget what hybrid you planted, you could wind up spraying a susceptible hybrid with glyphosate,” Bauer says. "Always plant resistant hybrids where they will bring the greatest return.”

Effective scouting. After planting, scout your fields. Carry a scouting manual with photos. Also carry a digital camera; if you're not sure about a pest, e-mail a photo to your consultant or Extension specialist.

Failing to identify a pest can have serious consequences. "One grower wasn't sure what insect was damaging his corn, but he went ahead and sprayed an insecticide,” Bauer says. "A week later, the problem was still there. It turned out the pest wasn't an insect—it was slugs, and the product he applied provided no control.”

Crop damage results from three factors: a pest, a host crop and the right weather conditions. "Understand which weather conditions favor various pests,” Bauer advises. "Watch the weather forecast for the coming week. It will give you an idea whether to
expect pest problems.”

Time your scouting to the crop's window of susceptibility—the period when a crop can be damaged by an insect. Susceptibility is based on crop height and condition. "For example, cutworms affect plants from emergence to the V6 stage,” Bauer says.
Corn borers are attracted to early or late-planted corn. "If you're the first in your neighborhood to plant, early flights of moths may be attracted to your fields,” Bauer says. "If all the corn in an area is already planted by the time you plant yours, late-flying moths may be attracted to your fields. Plan on scouting early or late-planted fields closely, or plant resistant hybrids.”

The info you need. Keeping track of heat units and growing degree days will help you determine when a pest outbreak may show up in your field. "You can put a weather station in your field, or you can visit Internet sites, such as and,” Bauer says. "Be sure you understand the difference between air and soil heat units.”

You don't necessarily have to know everything about every disease or insect to be a proactive pest manager, Bauer explains. You just need to know where to find the right information when you need it. "One good source is,” he says. "Among many other things, the site features pest alerts from various Midwestern states. You may be able to tell if a pest is moving your way.”

When you spot a pest, base treatment on economic threshold populations, Bauer concludes. "Remember that the economic threshold depends on the price of corn,” he adds.


You can e-mail Darrell Smith at

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