sealPurdue News

Februray 21, 1997

Soil-borne soybean diseases thriving, expert says

WEST LAFAYETTE, Ind. -- As soybean growers prepare for the 1997 planting season, they should check field notes from last year and bone up on ways to identify soil-borne diseases this summer, says Purdue University plant pathologist Don Scott.

"Yield losses in soybeans come from something you don't see -- from root damage," Scott says. "And early detection is the key."

Farmers who note disease invasions in a bean field should plan to plant resistant varieties, if possible, and should carefully plan crop rotations in subsequent years, he says. Their planting options are increasing as seed companies develop more and more resistant varieties, he says.

Soil-borne soy diseases that are on the rise in Indiana include soybean cyst nematode, new races of Phytophthora root rot, Pythium seedling blight, brown stem rot, white mold, sudden death syndrome and charcoal rot, Scott says.

"The disease organisms are slowly increasing in fields, especially in fields where corn-soybean-corn-soybean rotations have been used for several years," Scott says.

Root-damaging disease organisms can survive for several years in soil, Scott says. This is especially true of soybean cyst nematode (SCN), the state's biggest soy-stealing problem.

"The cysts of the soybean cyst nematode can survive in soils anywhere from three to 17 years. The nematode populations slowly build up until you finally see a significant problem," Scott says.

When the same crop is planted into a field year after year, or after only a one-year break, pests are still alive and lurking in soil.

"I can remember 40 or 50 years ago when rotations included corn, soybeans, wheat, and two years in alfalfa -- back when most farms combined livestock and row crops," Scott says. "The longer rotations helped keep many of these disease organisms at relatively low levels." By 1995, says Scott, about 70 percent of field rotations switched back and forth between only two crops: corn and soybeans. And 77 percent of fields had switched to reduced tillage.

"Economics dictated the changes," Scott says.

Economics is also driving farmers to take note of risks presented by pests and disease. Because government programs have removed some safeguards against crop loss, producers are looking harder for ways to manage their risks. Noting disease problems and planting resistant varieties is one way.

Source: Don Scott, (765) 494-4627; e-mail,
Writer: Rebecca J. Goetz, (765) 494-0461; e-mail,
Purdue News Service: (765) 494-2096; e-mail,

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