SCN Management Begins with Fall Sampling

October 18, 2007

WOOSTER, Ohio -- Fall is here and the time is near to soil sample for soybean cyst nematode (SCN).

The pest, which has a firm hold in Ohio fields, can damage soybean plants and quickly depress yields if not managed properly. The best way to begin managing SCN is to determine population levels through soil sampling.

"To effectively manage SCN, you need to know which fields have nematodes and how many nematodes are present," said Dennis Mills, an Ohio State University plant pathologist with the Ohio Agricultural Research and Development Center. "Sampling in the fall will give an estimation of the population levels on which to base management decisions for planting next spring."

Deemed the "silent robber of yields," SCN is the No. 2 soybean pest in Ohio, behind Phytophthora sojae, which causes Phytophthora root rot. Soybean cyst nematodes feed on the roots of young plants, which prevents the roots from taking up vital nutrients. The result is a drop in yields and subsequent economic losses.

"With SCN, you don't always see above-ground symptoms in Ohio. Growers just notice that their fields are not yielding as well as they have in the past," said Mills. "A grower may say, ‘That field used to give me 70 bushels per acre, now I'm getting 55 or 60 bushels per acre.' Well that's kind of a telltale sign. Growers just don't know that SCN is there, unless they sample for it."

Mills said soil sampling is inexpensive quick and easy, and is an accurate representation of any SCN activity in a grower's field. In order to prepare a soil sample, growers should follow these guidelines:

• Use a 1-inch diameter soil probe to collect soil samples (6-8 inches in depth).

• Following a zigzag pattern, collect 10-20 soil cores per 10-20 acres.

• Collect cores from areas of similar soil type and crop history.

• Dump cores from each 10-to 20-acre area into a bucket or tub and mix thoroughly.

• Place 1 pint (2 cups) of mixed soil in a soil sample bag or plastic zippered bag and label with a permanent marker.

• Store sample in cool, dark place until shipping.

• Send the composite sample to a lab doing SCN analysis, such as the C. Wayne Ellett Plant and Pest Diagnostic Clinic (http://ppdc.osu.edu), where the cost per sample is $15. Results report cyst counts per 100 cc of soil.

Mills said that growers should take great care when preparing soil samples. Several environmental and biological factors exist that can cause variability of SCN populations and yield inaccurate sampling results. Such factors include SCN population patterns, soil structure, cropping history, timing of egg hatch, survival tactics, tillage, and the presence of alternate hosts.

"Now is the best time to sample, right after harvest. The test is very simple and once you know the number of soybean cyst nematode eggs, your whole management plan is centered around that," said Mills.

Yield loss threshold of SCN in Ohio begins at 200 eggs per cup of soil. At 2,000 eggs per cup of soil, most susceptible soybean varieties suffer significant economic losses. At 5,000 eggs per cup of soil, growers should avoid growing soybean varieties altogether, even resistant varieties.

"The take-home management message is rotation, rotation, rotation," said Mills. "It's the most effective way of controlling SCN."

For more information on SCN management, refer to Ohio State University's Department of Plant Pathology Ohio Field Crop Diseases Web site at http://www.oardc.ohio-state.edu/ohiofieldcropdisease/soybeans/scn.htm.

Author(s): 
Candace Pollock
Source(s): 
Dennis Mills