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Soybeans Today January 2000

Disease screening ensures quality

By Fred Miller

Tamra Jackson, a U of A graduate student, examines soybean cultivars inoculated with stem canker.When soybean producers search through the tremendous number of varieties for the ones that will suit their fields, they need to keep disease resistance high on their list of criteria, says Terry Kirkpatrick, a University of Arkansas Division of Agriculture plant pathologist.

"One characteristic by itself doesn't make a variety successful, but one bad characteristic for a variety planted in the wrong place can ruin a crop," Kirkpatrick says.

"I think that some producers may be choosing a variety because one certain characteristic, for example Roundup resistance for weed control, stands out in their minds. This could be costly if the variety is susceptible to diseases or nematodes that may also be present."

An Arkansas Agricultural Experiment Station cultivar screening program supported by the Arkansas Soybean Promotion Board provides information producers need to know about disease resistance. Screenings this year revealed problems with stem canker and new hope for root knot nematode infestations.

"A greater number of varieties in our stem canker screen are showing susceptibility than in past years," Kirkpatrick says. "This may be because there are lots of new varieties in the screen, but many of the transgenic and conventional varieties are showing susceptibility.

"When producers look for a Roundup-Ready variety, they need to be sure they find one that also has any disease resistance they need," he says. "It would be a shame to have a nice weed-free field only to see the plants die because they were susceptible to disease."

Screenings also found some promising varieties for resistance to root knot nematode.

"This has been a good year for screening because dry weather shows root knot nematode damage more readily," Kirkpatrick says.

Bob Riggs, U of A nematologist, says nematodes infest a plant's root systems and distort the vascular tissue that transports water and minerals through the plant.

"The distortion impedes the movement of water through the plant," Riggs says. "In a wet season, or with irrigated fields, soybeans have the ability to resist or recover from damage. Non-irrigated soybeans in a dry year will show yellow spotting and stunting in the field that can result in considerable yield loss."

The Division of Agriculture screening program has identified a number of Group V soybean varieties that are resistant to root knot and soybean cyst nematodes.

"Several Group IV soybeans were included in the screening this year," Kirkpatrick says. "The majority of Group IV varieties are susceptible to root knot nematode, but we're finding a few that have some resistance.

"Caution is still the word for producers planting Group IV varieties," he says.

Before choosing any variety, producers need to know what nematode populations may be present in their fields.

"Fall sampling, after harvest, is a cheap and easy way to see if you need a resistant variety," Kirkpatrick says. "If I were a producer, it would be my goal to sample every field this fall before I selected any variety. Nematode populations are typically highest in the early fall."

Once producers know if nematodes or diseases are in their fields, they can find information about disease resistant varieties on the Division of Agriculture's SOYVA system or from county Cooperative Extension Service agents.

"The day you plant a crop is the last day you can do anything to protect against most of our most serious diseases and nematodes," Kirkpatrick says. "If you don't use all the available information about varieties to make your selection, you may be in for an unpleasant surprise."

Soybeans Today January 2000
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ATTN: Warren Carter
P.O. Box 31
Little Rock, AR 72203-0031
Phone: 501-228-1265

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