June 8, 2007

As soybean production moves west in Nebraska, so have soybean cyst nematodes (SCN), the most yield-reducing pathogen of soybeans. In 1986, SCN were identified for the first time in Nebraska in a field in Richardson County. Extensive random testing the next two years identified SCN in 10 additional counties, all but two of them bordering the Missouri River.

Over the years it has been difficult to convince many producers that SCN are more than a Missouri River valley problem or a problem they have to deal with at all.

Figure 1. Confirmed populations of SCN continue to move west into central Nebraska. Nebraska counties with confirmed SCN in 2004 are shown in black and the 14 counties where new SCN populations were confirmed in 2005-2006 are shown in red.

The Nebraska Soybean Board recognized this problem and partnered with University of Nebraska-Lincoln Extension to encourage soybean producers, field scouts and crop consultants to test for SCN by providing bags for a free SCN analysis ($20 value). This program has helped define the distribution and frequency of SCN in Nebraska. This year will be the third year of the sampling program. To participate, check with your local UNL Extension office for a free analysis bag. If bags are not available locally, contact Amy Ziems by email at aziems2@unl.edu or Debbie Pederson at (402) 472-2559, both in the UNL Department of Plant Pathology. Please limit your request to 10 bags.

This program has been very successful in identifying 14 additional counties where SCN has been detected. Twenty-one years after the initial detection in the state, SCN has now been identified in 41 counties representing three-fourths of the state's soybean production (Figure 1).

The program also has helped many farmers identify SCN and start managing it in their fields. About 24% of the samples have come back positive for SCN both years. Many participants indicated they had no idea SCN were present when they sampled their fields. Often they were trying to determine why yields didn't meet expectations or in some cases they just sampled out of curiosity.

What makes SCN so difficult to detect is yield losses up to 25-30% are common on healthy looking plants with no above ground symptoms. Often the first sign of a problem is when soybean yields hit a plateau or may even start to decline without other explanations such as weather, insects or herbicide injury. Frequently corn yields continue to increase in SCN-infested fields while soybean yields decline.

Keep reading CropWatch for details on four SCN Field Days that will be held later this summer near Concord, Mead, Newman Grove and Plainview.

John Wilson
Extension Educator, Burt County
Loren Giesler
Extension Plant Pathologist, Lincoln