To win the fight against soybean cyst nematodes, rotate crops, plant resistant varieties, and don't be sloppy about weed control, since some weeds are hosts.

But don't expect miracles, says Pat Donald, a University of Missouri extension nematologist.

"It's a long-term proposition. The way you manage nematodes is you starve them out gradually," Donald says.

Just remember that once they infest a field, cyst nematodes can't be totally eliminated.

The year after you discover SCN, plant a non-host crop such as corn, suggests Walker Kirby, a University of Illinois plant pathologist. "The following year, plant a soybean cyst-resistant variety. The third year, plant corn and retest."

If SCN numbers are below threshold, consider planting a susceptible soybean the fourth year. Then go with a corn-to-resistant soybean rotation the two following years, says Kirby.

"The idea behind using a susceptible is that we know there are different races or distinct genetic populations in Illinois and other states. We also know that if you go three to four years with the same resistant soybean in the field, you can shift the race from one that cannot feed on that bean to one that can."

Following resistant beans with resistant beans - rather than a non-host crop - can cause an even quicker race shift, notes Kirby.

Knowing what SCN race you have isn't important in picking a resistant variety because you may have several races within a field, Donald says.

Certain labs will test for race designation, but it takes a month to get results.

"We discourage it," states John Ferris, a Purdue University nematologist. "It's laborious and costly. Once the grower does know the race, the question is, 'so what?'

"We have four races here in Indiana, only one of which has seed labeled for resistance to it. Even if you have a race and plant a variety that says it is resistant to it, there's no guarantee that it will be resistant in that field."

Donald agrees.

"We know there is a lot of genetic diversity in the cyst nematode population. It isn't entirely a moot point whether you have a race 3 or race 5 variety. But, in general, it's better to have some resistance than no resistance."

So how does a grower pick a nematode-resistant variety?

Donald advises Missouri growers to look at variety trial results, especially if some of those sites are infested with SCN.

"Try to match geographically," she says. "Also keep in mind what the egg level is at that site compared to what's in your fields."

Other ways to combat SCN: keep plants as healthy and fields as clean as possible, Donald says. That means using good overall management and cleaning equipment between fields.

An option that's really not an option to hold back SCN is using nematicides, says Kirby.

"Number one, a lot of pesticides are water-soluble. If you get a heavy rain after application, it actually washes below the root zone," he says.

"Number two, some of these nematicides cause a rebound effect. They cannot kill 100% of the population. The individuals it leaves behind are now able to feed on a root system that is in top condition. More nematodes will reproduce and more will survive."