July 8, 2003
Source: Farm Press (FP) Online, 3 Jul 2003 [edited]

Cyst nematodes attacking Arkansas soybeans

The discovery of significant cyst nematode populations in central Arkansas has left producers and Extension personnel nervous and alert. Found in Prairie County around Des Arc and Hazen, nematodes have struck "sizable fields in a bad way," says agent Hank Cheney. He forecasts yield reductions from 10 to 40 percent, adding that it is either race 5 or race 6.

According to Chris Tingle, Arkansas Extension soybean specialist, you could pull a plant and immediately see cysts all over the roots in very high numbers.

Cliff Coker, Extension plant pathologist, points out that root systems are already injured and are now susceptible to soybean sudden death syndrome, charcoal rot, and other root pathogens.

Tingle says that not much can be done. "Picking up symptoms, identifying fields, and getting a race analysis -- which is what I'm begging producers to do -- is about all that can be done. The race must be identified. It will cost a bit up front, but the investment can be recouped easily by being able to choose the proper resistant variety and avoiding yield losses in future years."

Typically, nematode damage shows up at the end of July and into August. But producers began picking up symptoms last week when temperatures hit 95 degrees for the first time this year.

Coker says that "the only thing that producers can do is to not stress their soybeans further. That's especially true of water stress. So if an infested field can be irrigated, the producer should be very quick to crank up the pumps."

If the weather pattern the state is in continues, "producers should start looking for foliar diseases -- aerial blight, frogeye leaf spot -- at flowering. Another disease that we should be looking for is stem canker," he says.

Coker says the biggest problem producers face is lack of varieties resistant to nematode races now found in Arkansas. "I think we've backed ourselves into a corner by pushing for yield and ignored pests that can rob yield," he says.

"If you look at the majority of the varieties we recommend, they're resistant to Races 3 and 14," says Tingle. "We've done surveys in a number of counties to find out what races we have and 3 and 14 aren't the ones we have. We've got to work on our germ plasm because variety selection is our only defense against nematodes. This could easily become a statewide epidemic and we don't have a single tool to combat it."

[Byline: David Bennett]

[_Heterodera glycines_ (the soybean cyst nematode [SCN]) causes one of the most important diseases of soybeans. Yield losses of up to 30 percent, mainly because fewer pods are produced on infected plants. Moreover, soybean yield is directly related to the numbers of nematodes feeding on soybean roots. SCN-infected soybean is also more susceptible to infection by brown stem rot of soybean, caused by the fungal pathogen _Phialophora gregata_, in both resistant and susceptible soybean cultivars. Unfortunately, SCN cannot be eliminated from affected fields. Disease management involves providing plants with adequate moisture and fertility; implementation of sensible sanitation practices to prevent movement of the nematode to SCN-free fields; thorough cleaning of equipment by high-pressure water or steam; utilization of resistant cultivars; planting non-hosts such as corn, oat, and alfalfa so as to reduce nematode populations; and application of nematicides, which offer temporary control. A useful reference: <http://www.scncoalition.org/> - Mod.DH]