The best line of defense against nematodes is to use soybeans that are resistant to these troublesome microscopic worms. A screening program at the University of Arkansas Division of Agriculture identifies resistant varieties producers can use to protect their crops. The program screens for resistance to root knot, reniform and soybean cyst nematodes.
“Each year we take all the varieties in the Division of Agriculture Variety Testing Program and run them through greenhouse tests,” said Terry Kirkpatrick, UA plant pathologist. “More than 250 soybean varieties a year go through the screening.”
Kirkpatrick screens for resistance to root knot nematodes in greenhouse tests at the Southwest Research and Extension Center near Hope, Ark. Varieties that show resistance in the greenhouse are advanced the following year to a field nursery on the farm of producer Sam Whitaker of Dermott, Ark. The nursery screening is run by Extension specialist Cliff Coker.
“Sam had a field with a root knot nematode problem, and he lets us use it as a screening nursery because he's interested in knowing what varieties are resistant,” Kirkpatrick said.
He said greenhouse tests give a good indication of resistance, but the nursery helps define the subtleties of resistance and performance that are apparent only in a real-world field trial.
“Of more than 250 varieties we screened last year, only 20 showed enough resistance to advance to the field screening this year,” Kirkpatrick said. “So far, they're all holding up pretty well, so I suspect they'll be useful for producers with root knot nematodes.”
Plant pathologists Bob Riggs and Robert Robbins conduct greenhouse screening for reniform and soybean cyst nematodes at the Arkansas Agricultural Research and Extension Center in Fayetteville, Ark.
Kirkpatrick said the selection of resistant varieties is limited, but important.
“In the last five years that we've been doing these screenings, there have been only about ten varieties that are useful for resisting reniform nematodes,” he said. “That's about 1 or 2 percent of all varieties used in Arkansas. About 5 percent are resistant to root knot nematodes.”
“Many of our soybean cultivars show good resistance to race 3 of the soybean cyst nematode, and some have resistance also to other races such as 9 or 14. Unfortunately, SCN can occur in a field as any one of 16 different races,” Kirkpatrick said. “A variety that's resistant to one or two races may be less resistant or not at all for another race.”
Still, soybean producers' best bet for avoiding losses to nematodes is crop rotation with resistant varieties, Riggs said. “Especially following a year in which nematodes hit a field, producers should plant a non-host crop — cotton, corn or grain sorghum,” he said. “The following year to two years, they should plant varieties that are resistant to the race of nematodes that infests their fields. After that, nematode populations should be low enough to allow planting a susceptible variety that may provide higher yields for one year.”
Fred Miller is science editor for the Arkansas Agricultural Experiment Station. e-mail: firstname.lastname@example.org.