More than 200 soybean varieties that resist soybean cyst nematode (SCN) have been made available for the 2003 growing season. But you should still monitor SCN populations says Ohio State University (OSU).

Of the new resistant varieties, all but four originate from the same source. That tells OSU plant pathologist Anne Dorrance that, eventually, varieties from PI88788 will no longer be effective against SCN.

Dorrance says the barrier between SCN and certain resistant soybean varieties is already crumbling in limited areas of Ohio and will likely continue as SCN populations adapt to varieties that carry the PI88788 resistance.

“I think what growers don't understand is that resistance does not mean a complete resistance. The way soybean cyst nematode resistance is measured is by how many females reproduce compared to the susceptible check,” says Dorrance. “There will still be females reproducing on that resistant line, developing nematodes that eventually will develop an appetite for that particular resistant variety.”

The best way for growers to determine whether they should plant susceptible varieties or non-host crops is to test their soils for egg populations.

Although PI88788 has been the mainstay of SCN-resistant lines for the past decade, Dorrance says that growers should watch for the development of new lines that carry resistance, such as Peking and Hartwig.