By Greg Tylka, Department of Pathology and Microbiology, Iowa State University
The soybean cyst nematode (SCN) is one of the most damaging pests of soybean in Iowa and the Midwest. SCN can cause foliar symptoms of soybean sudden death syndrome (SDS) to occur earlier in the season and to become more severe, leading to increased yield losses from the disease.
SCN females on roots marks end of first generation
The appearance of SCN females on the roots of soybean plants usually occurs five or six weeks after planting in Iowa and represents completion of the first of multiple generations of the nematode in a growing season.
On Sunday, June 2, Tom Hillyer of Hillyer AgriServices in West Liberty, Iowa, observed emerging SCN females (see figure) on roots of susceptible soybeans that were planted on May 8. These soybeans were only in the V2 stage of development when the SCN females were observed.
Increased early SCN activity troublesome
It is unusual for SCN females to be evident on soybean roots so early in the growing season. Increased early activity of SCN is problematic because yield loss from SCN is directly related to their population densities in the soil, and SCN numbers may increase more if the generation time is shortened because more generations can occur in a growing season.
It has been reported that the wet spring weather may have resulted in an increase in the root rot phase of SDS for soybeans that were planted already this year (see June 4 ICM News article). The early appearance of SCN females on soybean roots, indicating increased early season SCN activity, also may increase the risk of severe symptoms of the foliar phase of SDS later this growing season.
Manage SCN for direct and possible indirect benefits
Managing SCN will reduce yield loss by lessening direct damage from the nematode and indirectly by possibly lessening the effect of SCN on SDS foliar symptoms. Management options for SCN include use of resistant soybean varieties and nematode-protectant seed treatments and growing nonhost crops such as corn in a rotation with soybeans.
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