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Corn+Soybean Digest


Caution flags are going up around the Midwest, warning farmers about the risks of “insurance” pest-control tactics.

The tried-and-true principles of integrated pest management (IPM) “are increasingly being ignored,” according to University of Illinois Entomologist Mike Gray. They are being replaced by “single-tactic approaches without any scouting input.” This shift away from integrated management could have some “very costly and negative consequences,” Gray warns.

IPM calls for monitoring pests, setting economic thresholds for treatment and deploying a mix of sound control methods. Yet, faced with escalating financial risk, more farmers are opting for “preventive or just-in-case measures” to protect their crop investments, says Ian MacRae, University of Minnesota entomologist. But “insurance treatments don't offer a greater economic return than scouting and applying pesticides when necessary,” MacRae says, and “in some cases, they actually return less. IPM was designed not only to ameliorate the impact of pesticides on humans and the environment, but — just as important — to provide the best economic return to producers.”

Here's what leading land-grant university experts have to say about some of these trends:

COMBINING HERBICIDE AND early soybean aphid treatments. Hoping to save a trip across the field, many soybean growers applied tankmixes of glyphosate plus insecticide last season, Midwest entomologists report.

So a lot of Midwest soybean acres were sprayed when aphid populations were still well below economic thresholds, says University of Minnesota Entomologist Ken Ostlie. There are other problems with this combination approach, too, says University of Minnesota IPM Specialist Bruce Potter. Nozzle, water volume and pressure settings vary for herbicides and insecticides. And the insecticide wipes out beneficial natural enemies, such as lady beetles, which help check aphids later in the season.

Many early treated Minnesota fields were recolonized in late July and August, and “a high percentage had to be sprayed again,” says Potter, who suspects that “insurance treatments helped make the aphid problem worse in 2008.”

This “clean-up-the-field” approach also backfired in Nebraska last season, where many soybeans had to be sprayed two or even three times, says Tom Hunt, University of Nebraska entomologist.

Likewise, in South Dakota, “It was popular to mix insecticide with early season Roundup,” says Kelley Tilmon, South Dakota State University entomologist, “but that's not a good practice. A single, well-timed application can often take the place of two poorly timed applications.”

In Ohio, where soybean aphids weren't a problem in 2008, “a lot of fields got sprayed with insecticide unnecessarily,” often in combination with a fungicide application, says Ron Hammond, Ohio State University entomologist.

Spraying when aphid levels are low is unlikely to increase yields, and the needless extra expense cuts your profit, Hunt says. Unnecessary spraying also raises the risk of developing insecticide resistance, Ostlie says. “The more times we treat the population, the more selection pressure we put on aphids.”

IPM tip: Scout before you spray. The economic threshold of 250 soybean aphids/plant with populations increasing still holds, even when soybean prices rise, Hunt says. However, higher crop values may cut a day or two off the window for treatment before aphids reach economic injury levels.

APPLYING FUNGICIDE WHEN no leaf diseases have been detected. Foliar fungicide use is soaring across the Midwest in both corn and soybeans, university experts say.

These applications are marketed “for plant health, but they're really prophylactic,” Ohio's Hammond says.

Foliar fungicides “are very good tools when there is disease present and it reaches economic damage thresholds,” says Ohio State University Plant Pathologist Anne Dorrance. But when it comes to preventive fungicide use, “long term, this is not a good thing for corn and soybean production.”

Fungicide overuse encourages the development of resistant pathogens, Dorrance says, “and we know that insensitivity to strobilurins can develop quite quickly.” Fungicides also kill the beneficial insect-attacking fungi that curb aphids, spider mites and other crop pests.

Midwest land-grant university trials have shown no consistent payback for fungicide applications when leaf diseases are absent, Dorrance says. In 2008 soybean trials in Ohio, for example, foliar fungicide produced a payback in only three of 31 locations, she says, “and in all three cases, foliar diseases were present.” In locations where it got dry later, she adds, spider mites exploded in the fungicide-treated plots.

Likewise, in 2007 and 2008 corn trials in small and large strip plots across the Midwest, strobilurin fungicide applied at VT-R1, when disease severity was low, produced a profit less than half the time, says University of Minnesota Plant Pathologist Dean Malvick. The results, summarized by Purdue University Plant Pathologist Greg Shaner, were drawn from 88 trials in 13 states and Ontario.

Although university research doesn't support preventive fungicide use in the Midwest, these products are nonetheless being “widely used by farmers to great benefit,” according to independent crop consultant Jerry Hartsock, of Cutting Edge Consulting and Research in Geneseo, IL.

A contrarian, he's skeptical of land-grant university fungicide research. “I'm seeing more success with fungicides in the field than they are seeing in their small-plot studies,” he says. Hartsock advises farmers throughout the Midwest and the Delta region for AgVenture and other seed companies.

Hartsock considers a preventive fungicide application at full tassel or early silk “a must” for all corn grown in the southern and central regions. In the northern region, he recommends preventive fungicide for continuous corn. He also recommends a preventive fungicide application at R3 for most soybeans.

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IPM tip: Before applying a fungicide, Dorrance says, growers should consider these questions:

  • Are there foliar disease symptoms?

  • Did you plant a variety with good leaf disease resistance?

  • Is rainy weather forecast?

  • Does the field have a lot of residue or a history of leaf diseases?

OVERUSE OF INSECTICIDAL seed treatments. Virtually all transgenic corn seeds and a growing number of soybean seeds are treated with neonicotinoid insecticides to control secondary pests, says Illinois' Gray.

“We're exposing a large portion of insects to this insecticide just in case they are out there at harmful levels,” Gray says.

Particularly in soybeans, says Nebraska's Hunt, “we're seeing quite a bit more of it than needed.” Growers feel these treatments are necessary to protect hefty seed investments and ensure good stands, he notes. “This is a case where insurance treatments are being used to manage risk — but often, the risk is not that great.”

In Nebraska, for example, many growers invest in neonicotinoid seed treatments to protect against bean leaf beetles. But it's only very early planted soybean fields that are at high risk from the pest, Hunt says. For beans planted at the normal time, infestations usually don't reach economic thresholds, so “we don't recommend it.”

Hartsock, the Illinois crop consultant, recommends seed treatments. “Even if no secondary pests reaches thresholds, cumulatively they can cause economic losses,” he says.

IPM tip: “Estimate your true level of risk,” Hunt advises. Insurance pest-management tactics should be limited to insects that are likely to occur, hard to scout for, cause severe economic losses and can't be well managed once they are present.”

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