Effective scouting during the growing season is the key to successful, integrated management of soybean cyst nematodes (SCN), says Iowa State University plant pathologist Greg Tylka.
"Symptoms of damage from SCN on soybeans could include stunting of the plants and yellowing of leaves," Tylka says. "But more than 30% yield loss can occur without the appearance of any symptoms.
Many Iowa fields are known to be infested with the SCN and many more are suspected of being infested," says Tylka, who adds that about 70 percent of Iowa’s fields may be infested with the persistent pest.
Soybean cyst nematode females can be seen on roots of soybean plants. Digging roots and looking for SCN females is an effective way to scout fields for this pest, Tylka says.
The SCN life cycle takes about 24 days to complete under ideal conditions, including soil temperatures of about 78 F. But depending on spring rainfall and soil temperatures, the first SCN females may not appear on soybean roots until 5 or 6 weeks after planting.
"To check for the presence of SCN females on roots, carefully dig roots from the ground and then gently shake or crumble soil away from the fine roots and look for the small, white dots that are the SCN females," Tylka says.
Assessing how many SCN females are on the roots of SCN-resistant soybeans provides an indication of how well the resistance is controlling reproduction of the nematode. There should not be more than 10 to 20 white SCN females on the roots of an SCN-resistant soybean variety if it is controlling reproduction of the nematode well.