Many of the soybean growing regions in the USA have been dealing with Soybean Cyst Nematodes (SCN) for many years. SCN was first detected in North Carolina in 1954, Minnesota in 1978, South Dakota in 1995 and North Dakota in 2002. SCN probably originated in China, Japan or Korea and was introduced into the USA in the late 1800's. It has been estimated that SCN is the most costly pest in soybean production nationwide. Once SCN is found in a field, it can't be eliminated. Good agronomic management practices like crop rotation and planting SCN resistant varieties will help reduce soybean yield loss to SCN.

Proper crop rotation is the most effective method of SCN management in the northern regions of the USA. Crop rotation options include planting SCN resistant soybeans, nonhost crops (i.e. small grains, corn, flax, sugar beet, potato and sunflower) and poor-host crops (i.e. alfalfa, red clover and peas). According to research conducted at the University of Minnesota in Waseca, by Dr. S.Y. Chen, "the effectiveness of crop rotation on lowering SCN numbers depends on the crop species grown, the number of years of rotation crops and geographic location." Geographic location is important because of the over wintering ability of SCN. In the southern USA, SCN populations are normally reduced to non-damaging levels within 1 or 2 years with proper rotations. But in the northern soybean areas the SCN goes into the deep freeze and is preserved until the soils warm. It may take over 5 years of proper crop rotation to reduce the SCN populations to low enough levels to plant a susceptible soybean variety without suffering yield losses in the northern soybean production areas. Planting susceptible soybeans or edible beans in an infested field will only increase the population of SCN. The most common crop rotation in many areas is corn followed by a SCN susceptible soybean variety. SCN levels will increase with this rotation and soybean yields will decline over the years. Planting nonhost crops or poor-host crops in combination with SCN resistant soybean varieties has been shown to reduce SCN populations and increase soybean yields over time.

Soil Testing for Soybean Cyst Nematode before or after Harvest

Fall is a good time to soil sample fields for SCN in the Dakotas and Minnesota, although sampling can be done throughout the fall, winter or spring. Summer sampling is probably the least effective time since SCN is actively growing and the population is in flux. SCN can go undetected for years, because many times visible symptoms do not appear until yield losses reach 30% or more. Visible symptoms of SCN shouldn't be confused with iron deficiency chlorosis (IDC) because IDC shows up early in the growing season, whereas SCN will show similar symptoms near the end of the growing season. Soil sampling from these "hot spots" just before harvest is a good way to confirm that SCN is present in a field. A composite field sample can be used to monitor the general population trend of SCN in the field.

SCN problems have increased dramatically in southern and western Minnesota and eastern South Dakota. SCN was detected in 70% of the samples analyzed at AGVISE Laboratories in Benson, MN in 2005. The 2005 AGVISE SCN summary can be found at www.agvise.com and by choosing the "2005 Soil Test Summaries" link. More complete information about SCN and other soybean management information can be found on the web at www.planthealth.info.