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Yields look promising for this Iowa soybean field

Factors like variety selection and pest management still remain key factors in boosting soybean yields. But there's still nothing like a 2-inch rain during pod fill to also boost yields.

That's the situation John Fredrickson was in when we stopped by his farm on Aug. 14. The Gowrie, Iowa, farmer enrolled a 41-acre field in the High Yield Team program for 2006. It's a field in which we've asked Palle Pedersen, Iowa State University Extension agronomist and High Yield Team expert, to follow during the growing season.

Bean leaf beetles
Moisture has been sparse in Fredrickson's area this year, but a two-inch rain the second week of August, followed by .6 inches the weekend of August 12-13 has perked up his soybeans considerably.

Pedersen liked what he saw as he eyed pod development. At this point, it was difficult to pin down a yield estimate, "but it's not going to be below 50 bushels of acre," he says.

There's a big however, though, in the form of bean leaf beetle. The second generation of this pest is making its way throughout Iowa. That message was reinforced while Pedersen was sizing up Fredrickson's soybeans.

"Just as I looked at that plant, I can see four beetles on it," said Pedersen as he talked with Fredrickson. Bean leaf beetle numbers were increasing to the point where spraying was advisable, says Pedersen.

"If I was your crop consultant, I would line you up with a sprayer," he says. "You have yields to protect."

Pedersen says if there is a mild winter, bean leaf beetle infestations could jump in 2007 in Iowa. Bean leaf beetles can plague soybean growers several times during the growing season. The bean leaf beetles that emerge in early spring around planting time are the overwintering generation. The first generation, which are the first beetles born that year, show up around early July and lay eggs for the second generation, which often appear during pod fill.

One of the way beetles damage soybeans is through plant feeding, particularly causing damage via pod eating during pod fill. However, all three generations can also slice yields by spreading bean pod mottle virus (BPMV). Yield damage by this virus often is hidden, with no visible symptoms. That's why Petersen says it's so important to monitor this pest now and treat if thresholds are reached. Economic thresholds for the second generation (the generation now threatening crops) are made by beetle surveys during the first generation. (For more information, go to Go to insects and mites, then bean leaf beetle).

Good news
Outside of bean leaf beetles, there's plenty of good news for Fredrickson. Sudden Death Syndrome (SDS) -- which afflicted some of Fredrickson's fields last year -- has been absent this year.

"Last year, we'd see spots in fields where everything was dying early," he says. "We haven't seen that this year."

Soybean aphids also have not been a problem in Fredrickson's region. There have been areas where soybean aphids have risen to threshold levels, such as in eastern South Dakota. But by and large, Pedersen notes that aphids are continuing their high-low two-year cycle, with 2006 being the low portion.

Weed control also has been a bright spot for Fredrickson this year. He applied a full rate of Tri-4 (containing the active ingredient trifluralin) preplant that was followed a full postemergence rate of Roundup WeatherMax the week prior to Independence Day. The Tri-4 application gave excellent residual control prior to the final postemergence application.

"Once in a while, you'd find some waterhemp in there (before the Roundup application), but that was it," says Fredrickson. "There are cheaper programs out there, but this one works for us."

Fredrickson has dealt with soybean cyst nematode (SCN) by planting an SCN-resistant variety that's also tolerant to iron chlorosis. Planting an SCN-resistant soybean on SCN-infested soils is an important key to boosting yields, says Pedersen.

It's not recommended growers load up with numerous defensive characteristics when selecting varieties, since that can curb yield potential. "What you want to do is key in on the top two characteristics," says Pedersen. "In northern Iowa, it's brown stem rot and soybean cyst nematode. For the southern two-thirds of Iowa, it's soybean cyst nematode and sudden death syndrome."

Another factor in Fredrickson's corner was a picture-perfect planting season. He was able to plant the field he enrolled in the High Yield Team project on April 28, in line with the recommended April 25 starting planting date for the southern two-thirds of Iowa.

Meanwhile, Fredrickson's dense soils have been able to make the most of sparse moisture this summer. "Our soil types hold moisture and keep it," he says.

The potential for soybean yields look good for Fredrickson's area and Iowa in general, says Pedersen. "We'll have a tremendous crop (in Iowa) if we can manage bean leaf beetle," says Pedersen.

Factors like variety selection and pest management still remain key factors in boosting soybean yields. But there's still nothing like a 2-inch rain during pod fill to also boost yields.

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