Published: August 27, 2008 10:41 am            

Timing critical for control scourge of soybean aphids

Originally published in the August 22, 2008, print edition.

Soybean growers remember 2003 when aphid populations exploded across Minnesota soybean fields and aerial applicators from other states flew to Minnesota to help in-state pilots fight the sudden onslaught.

Though it’s not quite as bad this season, said Bruce Potter, University of Minnesota Extension pathologist at the Southwest Research and Outreach Center at Lamberton, airplanes are flying, often early in the morning to late evening, depending upon prevailing wind conditions.

At the Extension information tent at Farmfest, Potter indicated aphid infestations were across Minnesota but surrounding states are also now spraying. “At this point it’s a general Upper Midwest problem,” he said.

Several different products are available for controlling the insect but synthetic pyrethroids and the organo phosphates (such as Lorsban) are the two basic chemistries. Some seed treatment with Cruiser is being used.

“The problem is short-lived control with seed treatment,” Potter said. In plot work at Lamberton in past years, he indicated by early August there was no control left yet the winged aphids were still persisting. “Seed treatment buys you some time, but we’re not seeing season-long control and that’s the issue.”

Timing is critical

Potter pointed out that with proper timing, one spray can do the job. But this year a lot of “assurance” treatments went on, often just a bit too early, and those fields are now being resprayed.

“Even fields that were sprayed at early threshold levels are needing to be resprayed right now. It’s a tough year. Anyone who sprayed their soybeans two weeks ago I suggest they check their fields again. I hate to have anyone surprised on the back side now.”

Part of the dilemma is that many farmers added an insecticide with their second Roundup spray as an early preventive for aphids. That’s not always working. A producer just can’t accurately predict the movement and weather patterns that accelerate the aphid populations.

Potter acknowledges that the cost of an insecticide application isn’t a huge part of total production costs and even a one-bushel difference with $12 beans makes it work on paper. However, the need for multiple applications can really eat at the bottomline. Ground and/or aerial applications are costing $10 to $11 per acre.

What if no treatment?

How much yield loss without treatment? Up to 50 percent reduction in yield trials are documented at various U of M research trials. Tack that against a potential 60-bushel soybean yield at today’s prices and aphids are indeed financially disastrous.

Again Potter cautions about the importance of timing and monitoring your fields. Apply the insecticide too early and that 50 percent yield loss can still hit that field, he said.

Can genetics eventually come to the rescue of this troublesome and most costly insect problem? Yes, but not yet.

Potter said “resistant lines” have been tested at Lamberton and elsewhere but nothing is yet ready for Minnesota maturities. “They’re not bullet proof. Often the aphid population simply overwhelms the plants resistance. But it’s another tool in the battle.”

At Farmfest the Dahlco Seeds variety plot did show an aphid resistant soybean but it was a 2.8 RM, way too late a bean for Minnesota climates.

“In this age of high-cost production agriculture, it’s pretty obvious that doing things by the calendar isn’t the answer for aphid management. We need to get into a more total system of chemical, cultural and genetic tools. In essence throw the whole ball of wax at this aphid challenge just to keep this thing manageable,” Potter said

So if farmers, crop scientists and commercial developers do the right things and Mother Nature cooperates, can 80-bushel soybeans become common in Minnesota?

Potter believes so.

The reason yields aren’t this strong is not the genetics of the seed but rather just a few “mess ups” on planting dates, fertility, planting rates and obviously “yield protection” programs involving chemical applications, etc.

“We’re seeing soybean yields on the increase but two potentials cloud the horizon: 1) shifting races of soybean cyst nematodes, and 2) some of the diseases such as phytophthora are changing so the genetic resistance lessens. Breeders are doing a great job on genetic yield increases. The pest issues keep disrupting some of this trend-line progress,” Potter said.

Potter’s crystal ball

With commodity markets still strong, especially on soybeans, which crop does Potter feel will see the most increase in acres in 2009.

Not being an economist, he didn’t first venture with “well that depends,” but he did say that the corn-soybean rotation works so well for so many Minnesota farmers that he doubts there will be any significant shifting from one crop to the other.

“We don’t always know where energy demands, global markets, even sudden new uses for the crops will drive things. Who knows? No one for sure, it could be wheat and soybeans 10 years from now. But regardless, farmers are terrific at adapting providing there are profit opportunities in that crop mix, whatever it may be.”

        

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