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Soybean predators: Nature behaving naturally
March 31, 2003
By Nancy L. Torner
Center for Rural and Regional Studies
Text version of this story

Soybeans just are not adding up for Mike Hewitt.

"We're having a terrible time growing soybeans -- disease, insects -- so we're trying something different," Hewitt, who farms 1,200 acres near Walnut Grove, said in a recent interview.

This year, Hewitt is planting some wheat instead.

"Hopefully, by planting wheat, we're going to pick up yield on our corn and our soybeans later on by staying out of those crops long enough," Hewitt said. "That's what we're planning on, anyway."

Hewitt has company. Seed representatives say they are seeing a small, but noticeable decline in soybean seed sales this year. Lower yields are part of the reason.

"It used to be pretty easy if you took your corn yield and divided it by a third, that was what your soybeans should yield, and I don't think we're seeing that anymore," Jerry Louwagie, a sales representative for Monsanto said.

Farmers harvested 7.1 million acres of soybeans statewide in 2002, for an average yield of 43.5 bushels per acre and total production of 309 million bushels, according to the Minnesota Agricultural Statistics Service. Despite this record yield, dwindling production plagues different farmers across southwest Minnesota.

"It's kind of like the movie 'Field of Dreams,'" Bruce Potter, an integrated pest management specialist in the entomology department at the Southwest Outreach Center in Lamberton, said. "If you grow more and more soybeans, over time, things will come in to utilize soybeans as a food source. It's just nature behaving like it's supposed to."


Weather drives ag enemies
     Accurately predicting what problems might plague crops this year is harder than predicting the weather, and weather drives the biological processes that affect crops.
     Yet people are far more forgiving of faulty weather predictions, Bruce Potter, an integrated pest management specialist in the entomology department at the Southwest Outreach Center in Lamberton, said.
     "It's much better to be a climatologist because people are much more willing to forgive miscalculations in that area than they ever are in me saying we're going to have a bean leaf problem or a corn bore problem," Potter said.
     According to climatologists for Salomon Smith Barney, this spring should bring moisture. Based on weather patterns dating back 108 years, springs that follow an El Nino event typically have a wet bias, according to data from the firm. With only one exception in 1928, extreme dryness in winter has broken in April or May.
     "If the biological model that we use is right, there should be a lot less problems with the bean leaf beetle," Potter said. "Again, that's a model and I won't swear to that until I see the bean leaf beetles this spring."
     Potter expects little change in corn rootworm populations. Meanwhile, corn bores are picking up, more in the east than west, but this could change in summer.
     "If it's wet, especially early in the season, we'll have root rot problems, and it depends on whether it's hot and wet or cold and wet which ones are the big issues," he said. "If it's cool and wet during flowering, we'll probably get white mold."
     Potter isn't making any predictions about soybean aphids, but he notes they are able to over-winter, at least in the southern two-thirds of Minnesota. Other pests, such as inch worms, can't survive winter but move into the state from the south.
     "Problems depend on the weather," he said.
-- Nancy L. Torner
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Problems range from leaf beetles, aphids and mold to root rot, iron deficiency chlorosis and tiny worms called cyst nematodes. And last year, a soybean disease called sudden death syndrome showed up in the state for the first time. The severity from year to year depends on a range of factors, such as soil type, water, planting practices and weather.

"Everything is here to stay, and what it means is if we keep growing soybeans, for example, we just have to be better at managing," Potter said. "And that means more inputs as far as developing genetics, and it also means more inputs as far as people having to manage things, watch what crops they have in the fields, maybe change rotations to counter certain problems."

Tillage makes some problems worse and others better, and it has no affect on still others, he said. For instance, tilling might help root rot by drying out soils, but fungicide trials show that heavily tilled land sometimes performs worse because it can compact soils more.

Adding a third crop rotation can help some problems, but no single crop is the answer for the region, Potter said. It depends in part on a farmer's mindset and requires weighing the long-term benefits of an added rotation.

"What happens is everybody looks at things one year at a time, and that's where we get into trouble," Potter said.

It also depends on what farmers think they can sell and the steps they take to sell it, said Jim Orf, a professor in the department of agronomy and plant genetics at Minnesota State University who works on developing soybean varieties.

"There aren't as many crops that really look all that good, at least from an economic standpoint," Orf said.

This might change depending in part on the farm bill, which has a large impact on what people plant. Soybeans are less favorable than before, and with lower yields, other crops might look more attractive, Orf said.

"Farmers need to look at the specifics of their local situation and try to take advantage of what opportunities might be there on a local basis," Orf said. "There are opportunities pretty much any place, but it takes a little leg work or some phone calls, some effort."

Extension offices don't have all the answers, but they can help, Orf said. Studies and testing are ongoing to help improve yields and resistance. He tests soybeans from the public sector for such things as yields, resistance and the content of oil and protein and publishes results in the Variety Trials Bulletin.

Salliana Stetina, a plant pathologist at the Lamberton Center and an assistant professor in the agronomy program at Southwest State University (SSU) in Marshall, is studying ways to diversify the crop system and to add a cover crop without taking away from the regular crops. Her primary concern is cyst nematodes, one of the region's major problems.

Cyst nematodes first surfaced in the 1950s in North Carolina. They infiltrated southern Minnesota in the 1970s and now exist all the way up to the Red River Valley, she said. Wind, water, animals and farm equipment all help to transport them. Changing rotations won't kill them because they are capable of remaining dormant for a decade or longer, but it will lower their numbers.

Cleaning farm equipment and tools, working non-infested fields before infested fields, planting lower yield varieties with some resistance and alternating varieties are helpful also, she said. However, limited diversity among soybean plants restricts choices, and alternating suppliers is no guarantee varieties are different, Stetina said.

"You think you've got two different suppliers, but there's a lot of overlap in the genetics," Stetina said.

Iron chlorosis, an iron deficiency problem, is another major drain on soybean yields in southwest Minnesota and parts of South Dakota and Iowa, said Lori Scott, an assistant professor in the agronomy program at SSU. She is field-testing varieties for tolerance to this condition. She also is testing seeds with extra iron and studying the best concentration of plants.

"We know that when plants are more densely populated, they sort of help each other overcome the problems," Scott said.

Testing is entering only the third year, too early for any planting recommendations, she said.

"I'm always looking for collaborators," Scott said. "I usually ask (farmers) for about an acre of really bad land."

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