The soybean cyst nematode is widely considered to be one of the most damaging soybean pests in Iowa every year. Damage from SCN is usually much greater when soil moisture is limiting. The early onset of stunting and yellowing caused by SCN damage in Iowa this season seems to indicate that yield loss to this pathogen is going to be significant – perhaps even on SCN-resistant soybean varieties.
That's the word from Greg Tylka, Iowa State University Extension nematologist, based on his observations this summer. He offers the following insight and guidelines.
"As if the direct effects of Iowa's hot, dry growing season on crops were not damaging enough, the soybean cyst nematode probably will be more damaging this year than in the past two decades due to the lingering drought conditions," he says.
Symptoms of SCN damage to soybean plants are appearing sooner this year
Damage from SCN does not always cause aboveground symptoms, especially in years with adequate to excess moisture. But when symptoms occur, they usually appear in mid-to-late July (see 2011 ICM News article here).
This season, stunting and yellowing of soybean foliage caused by SCN feeding has been apparent throughout the state since late June, which is much earlier than usual.
Symptoms of SCN damage can be relatively mild when SCN population densities, or numbers, are low. But stunting and foliar yellowing can be severe in very dry soils and when SCN population densities are high (Figure 2). The earlier those symptoms appear in the growing season and the more severe they become, the greater the yield loss that occurs with SCN.