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Battle for the beans: Farmers must watch for diseases after planting

Sunday, June 1, 2003

SIKESTON -- Many area farmers are working around the clock and taking advantage of the warmer and drier weather since they began planting soybeans late last week.

But in a farmer's world, getting the crop planted is only half the battle, especially when unpredictable weather and disease worries are sure to follow.

"Right now there isn't as much concern with disease because it's still drying out and not many beans were planted due to the rain, said Grover Shannon, soybean breeding expert at the University of Missouri Delta Research Center in Portageville. "We've had an unusually cool and wet May, which isn't the best condition for farmers to plant soybeans, or any crop for that matter."

The optimum temperature for soybeans to germinate is 85-88 degrees, Shannon said. Conditions are getting to be just about right for planting, he said, adding that it's a little late, but there's still plenty of time to get soybeans in.

"In the coming weeks, farmers should watch for areas where the crop is stunted and a different color. Pay attention to patterns of symptoms of lower leaves that have brown to black spots that may become tattered," advised Allen Wrather, professor of plant microbiology and pathology at the University of Missouri-Delta Center.

Two diseases present in most Southeast Missouri soybean fields are causing these symptoms -- brown spot and bacterial blight. These diseases may be less visible in some varieties than others. Fortunately, neither of these diseases generally cut yield in this area, Wrather said.

Both of these diseases spread in warm-rainy weather and will stop spreading during the hot dry weather typical of July and early-August, Wrather explained.

So be on the lookout for problems in your fields. There are problems out there that are of little consequence but others can reduce yield, Wrather warned.

"A few weeks from now will be an excellent time for farmers to walk over soybean fields and look for problems," noted Wrather. "It will be hot and require some time, but farmers may observe problems to look into later."

For example, symptoms of low pH, compacted soil, nutrient deficiencies, soybean cyst nematode, root rot and herbicide carryover may be visible, Wrather said.

Soybean cyst nematode (SCN) is the worst pest of soybeans in the United States, and the situation isn't getting any better, according to Wrather.

The most recent available figures showed losses to SCN in the United States including Missouri, Illinois, Kentucky, Arkansas, Tennessee and Mississippi totaled about $681 million. The good news is that these losses can be reduced by planting resistant varieties and rotating soybean with corn, cotton or grain sorghum, Wrather said.

Crop rotations work great for reducing SCN populations. "When we grow soybean one year, then switch to corn or another crop for a couple of years, we can pretty well manage SCN. We also reduced SCN populations in the northern research sites with crop rotation, but not as much as we did in the southern areas," Wrather explained.

Another soybean disease, frog eye has been a menace, Shannon pointed out. There was a good bit of it in Southeast Missouri last year, but farmers just never know if the warm humid conditions will occur for it to develop every year, he said.

Currently, Shannon and his colleagues are working on improving soybean varieties' resistance to frogeye leaf spot. "We've planted over 400 varieties which will be inoculated with frogeye leaf spot this year," Shannon said. "This is a preliminary round to determine which varieties have the best resistance for our growers."

Shannon said performance results will be available for farmers by next spring.