Take action now to fight SCN

Soybean cyst nematode continues to spread north. SCN is present in many eastern and central South Dakota counties. This year, we discovered a field in the Red River Valley by Kent, Minn., and I’ve heard of other fields recently identified in Barnes and Trail counties in North Dakota. These are in addition to locations found previously in Cass and Richland counties in North Dakota.

SCN is most commonly spread through the movement of soil from an infected field to a non-infected field, usually on tillage or harvest equipment. Sugarbeet growers really need to take care to move as little soil as possible during harvest of that crop.

SCN is still the No. 1 yield robber in soybeans. Yield is frequently reduced even before symptoms are visible. By the time symptoms are noticed, cyst levels are usually high, and pest management is extremely critical.

Key Points

• Soybean cyst nematode is spreading into South Dakota and North Dakota.

• SCN moves from field to field in soil on tillage and harvest equipment.

• It’s important to test for SCN and follow best management practices.

Since most growers test their 2010 soybean fields in the fall in preparation for next year, now is a great time to also screen for SCN. Take 10 to 20 cores about 6 inches deep and mix before submitting. If you just want to sample to determine if cysts are present, take cores near the entrances to the field. Approaches, ditches and areas along streams and rivers are a good place to start. If you use yield mapping and have noticed some lower-yielding spots without an apparent reason, you may want to test those areas as well.

SCN is sometimes mistaken for chlorosis in soils prone to iron deficiency chlorosis. That is actually how we found SCN in the field near Kent. One of our better varieties for IDC, 0908RR, was planted on that ground and unusual yellow spots showed up this summer. We soil tested in both the good and bad spots and also sent in a SCN test. The SCN test came back at 2,000 eggs per 100 cubic centimeters of soil.

University of Minnesota management recommendations are:

• Less than 200 eggs per 100 cc of soil: Plant a susceptible variety.

• 200-2,000 eggs per 100 cc of soil: Plant a resistant variety.

• 2,000-10,000 eggs per 100 cc of soil: Plant a resistant variety, but yield loss may occur.

• More than 10,000 eggs per 100 cc of soil: Don’t plant soybeans, even a resistant variety.

While SCN cannot be eliminated entirely, yield losses can be minimized by utilizing best management strategies. First, identify whether SCN exists. If it does, always plant a resistant variety. Crop rotation is also important. Rotating to a nonhost crop such as corn, small grains or alfalfa will help reduce egg-count levels. Be sure to continue soil-testing every year to determine if the cyst levels are decreasing.

Because SCN started in the south, soybean breeders saw the problem spreading north and have been working on getting SCN resistance into good genetics in order to be ready. So be prepared by checking your fields. Don’t let SCN rob your yields.

Spelhaug is an agronomist with Peterson Farms Seed, Harwood, N.D. Contact him at 866-481-7333 or visit www.petersonfarmsseed.com.


SCN SIGNS: Tiny soybean cyst nematode cysts appear on roots in infested soil.

This article published in the September, 2010 edition of DAKOTA FARMER.

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