The Cost of Insect Control

MT. VERNON, Ill. (DTN) -- If they weren't hibernating, the insects of Illinois would have been pleased to hear University of Illinois entomologist Mike Gray urging local growers to reel in their insect management costs in 2015.

In light of narrowing profit margins, growers should scrutinize insect control measures such as Bt corn hybrids, treated soybean seed, and routine insecticide passes, Gray told a crowd of southern Illinois producers at a Corn and Soybean Classics presentation on Jan. 14.

"I'd like you to think through very carefully some of your insect management input decisions," he said. "Are your Bt seeds and insecticide applications going to be necessary and produce increased profitability in 2015?"

RECONSIDER BT

Bt hybrids fill most seed company catalogs, but not all growers deal with the pest populations those hybrids target, Gray pointed out.

European corn borer, while far from extinct, exists at very low levels for most Illinois growers. In 2014, corn borer sweeps in Illinois uncovered numbers so low that the highest collector clocked in at just 0.6 moths per 100 sweeps, Gray said.

Yet, 80% of the corn planted in the U.S. contains Bt proteins, many of which target the corn borer, Gray noted. "Why are we planting so much Bt corn when some of these numbers are so low?" he asked.

Several farmers in attendance noted a common complaint in the search for non-Bt hybrids: lack of top-quality genetics. "While you're talking, I'm texting my dealer and he is telling me the hybrids I've chosen this year are not available in non-Bt," one farmer remarked.

Gray conceded that farmers may run into difficulty during hybrid selection, but insisted that the effort would be worthwhile. "I think folks have to have that conversation with your seed supplier," he urged. "There are a lot of [Bt] proteins being expressed out there that are not of value to you."

For growers in the heart of Illinois and parts of Iowa and Minnesota, populations of Bt-resistant western corn rootworm continue to cause problems. The most recent research from the University of Illinois has confirmed populations of rootworms that are resistant to two Bt proteins (Cry3Bb1 and mCry3A). In some areas of Illinois, these same pest populations have also been able to overcome crop rotation, Gray said.

Growers in these hotspots should also scrutinize their 2015 corn hybrids carefully. "For the northern two-thirds of Illinois, the odds are that you've got a resistant population of Western corn rootworm that these proteins [Cry3Bb1 and mCry3A] are not going to work all that well against," Gray explained. "So if you are interested in rootworm protection, make sure you know what [Bt] protein is being expressed."

UNTREATED BEAN SEED

The EPA report disputing the need for neonicotinoid seed treatments in soybeans for Midwestern growers should serve as a wake-up call, Gray told growers. Industry has pushed back against the report, but Gray and 17 other land-grant university entomologists recently sent a letter to the EPA expressing their support for most of the significant findings in the report, Gray said.

"I think in regards to soybeans, much of what they're saying is true. There is relatively limited to no economic benefit from the use of insecticidal seed treatments in soybeans," he told growers. "Coupled with the potential negative environmental consequences, I have to ask: Why are we using these tools so often?" Gray said.

According to the EPA report, neonic insecticide seed treatments cost an average of $7.50 per treated acre. Growers should pay careful attention to their insect problems and determine whether pests targeted by these treatments, such as white grubs, wireworms and bean leaf beetles, are likely to be an economic threat, Gray concluded.

While nearly all corn seed on the market is treated with insecticides, the EPA report estimated that only 30% of soybean seed has been planted with a neonic seed treatment between 2008 and 2012. That means growers should be able to request untreated soybean seed from seed suppliers.

Members of the audience noted that marketing may continue to play a role in farmers' decisions to use treated soybean seed. "Seed companies are pushing treated seed," one farmer pointed out. "As a selling point, they guarantee full replant if you pick treated soybean seed."

You can find the EPA report on neonicotinoid use in soybean seed treatments here: http://goo.gl/…. The report has been reopened for comment until Jan. 23, 2015.

REIGN IN SPRAYING

Cutting back on insect control requires a lot of legwork, Gray noted. To reduce routine insecticide passes, farmers will have to scout regularly and comprehensively to ensure that insect populations are below economic threshold levels.

"Unfortunately, we've seen lots and lots of treatments being applied, while year after year, our surveys have shown very low levels of insect densities out in soybean fields," he told growers.

University of Illinois trials of insecticide treatments for pests such as soybean aphid, bean leaf beetle, and Japanese beetles consistently show little to no yield impact from treatment, Gray said. Soybean aphids, for example, must be at very high levels before the crop's final yield will suffer.

"Remember that the threshold for soybean aphids is around 250 aphids per plant, but when economic loss begins to take place is probably about 1,000 aphids per plant," he said.

Japanese beetle damage is measured by defoliation levels. Given the alarming sight of a skeletonized soybean leaf, most farmers overestimate the percentage of defoliation, Gray noted.

Spraying shouldn't occur before 20% to 30% defoliation. "I'm quite convinced that a fair amount of spraying takes place in just the 5% to 10% defoliation range, and that's not likely to pay you back," Gray pointed out.

Some insects, such as Japanese beetles, tend to cluster along field edges and end rows. Scouting an entire field can help a farmer save money by limiting an insecticide pass to the infested areas, Gray added.

"Acquaint yourself with the biology of these insects and their thresholds because treating them will be very, very important decision for growers to make this year," Gray concluded.

You can find results of the University of Illinois' annual insecticide and fungicide trials here: https://ipm.illinois.edu/….

Emily Unglesbee can be reached at emily.unglesbee@dtn.com.

Follow Emily Unglesbee on Twitter @Emily_Unglesbee.

(PS/AG/SK)

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