The soybean cyst nematode, commonly referred to as SCN, is a major yield-limiting pathogen of soybeans in Iowa. The nematode is a microscopic worm that lives in the soil and was particularly damaging in the 2012 growing season because of the drought conditions. Thorough knowledge of SCN biology is the foundation for successful long-term management of this pest.
The "Soybean Cyst Nematode Field Guide" was first published and distributed by Iowa State University and the Iowa Soybean Association in 2008. The durable, pocket-sized book contains information about the biology of the nematode, as well as scouting methods, management strategies, disease interactions and the HG type test.
A revised, second edition of the "Soybean Cyst Nematode Field Guide" is now available.
Updated and new information: Information and images throughout the publication have been updated in the second edition. Also, new information added to this second edition includes discussion of:
* effects of drought on SCN biology and damage
* development of SCN populations with increased reproduction on PI 88788 resistance
* seed treatments as a management tool
Where to get copies: Individual copies of the second edition of the SCN Field Guide can be obtained at no charge from the Iowa Soybean Association by calling 800-383-1423. Copies also will be distributed to Iowa farmers at ISU Extension Private Pesticide Applicator Training sessions this winter. Single copies of the revised field guide can be obtained at no charge from ISU Extension and Outreach field agronomists. The revised field guide is available for purchase from the ISU Extension Online Store (CSI 0012) and it is available there as a downloadable PDF file.
Soybean yield loss from SCN is considerably worse in very dry years
"The severity of symptoms and yield loss caused by SCN is affected greatly by availability of moisture during the growing season," says Greg Tylka, ISU Extension nematologist. "Aboveground symptoms of SCN damage can be quite severe in dry years, but mild or nonexistent in years with adequate or excess rainfall. SCN stunts the soybean roots, which is much more harmful to the soybean plant in drought years than in years of adequate or excess soil moisture as stunted roots explore less soil for water and minerals than normal-sized roots."
There are indications that SCN reproduction may be greater in dry soil conditions than in wet soils. Hatched SCN juveniles enter soybean roots and set up permanent feeding sites, called syncytia, inside root tissue. The SCN juveniles possibly establish feeding sites deeper into the root vascular tissue under dry soil conditions than wet conditions.
And the nematode feeding sites may be considerably more disruptive to root function if they are located in the vascular tissue rather than in the outer cortex region of the roots. Also, SCN juveniles feeding in the vascular tissue may have better nutrition than those feeding in the root cortex, possibly leading to greater SCN reproduction.
Good reasons to manage this pest and not let it get to high populations
"Yield loss from SCN is considerably worse in drought years," sums up Tylka. "SCN reproduction may be much greater under these severe growing conditions as well."
SCN cannot be eliminated from an infested field if soybeans are ever grown again in that field. "Once SCN is discovered, a management program should be implemented immediately to minimize SCN reproduction and maximize crop yields," says Tylka. "The
goal of an SCN management plan is to maintain profitable soybean yields while keeping SCN population densities at low to medium levels."
It is much easier to keep low SCN population densities low than it is to drive high populations down, says Tylka. SCN management can involve:
• Growing nonhost crops
• Controlling winter annual weeds
• Applying nematicides to the soil
• Using nematode-protectant seed treatments
• Growing SCN-resistant soybean varieties