October 26, 2007

Free Tests Available

While you can test for soybean cyst nematode (SCN) any time, post-harvest provides an opportunity to test when poor yielding soybean fields or areas within soybean fields are fresh in your mind. In the fall you should be able to easily move around in fields and sample areas next to the old soybean rows. If you find SCN, you'll still have time to switch your seed to an SCN-resistant variety, if warranted.

Another benefit is that your local UNL Extension office may still have sample bags available for a free SCN analysis. This represents a $20 value. This testing program, funded by the Nebraska Soybean Board, has been successful in helping farmers test and identify SCN in new areas of the state. Most farmers who had samples come back positive for SCN had no idea it was in their fields.

To take a sample, either pull 20-25 soil cores from random areas or target problem spots you suspect may have SCN infestations. Problem areas include: 

• flooded areas,
• areas along fencelines,
• near field entry points and
• low areas within a field where water may stand or drain.

SCN infestations are most likely to be found in field areas where corn yields are fine, but soybean yields don't meet expectations and these low yields can't be explained by factors such as compaction, soil type, herbicide injury or erosion.

SCN can be difficult to detect because it can cause significant yield losses, up to 30%, without causing any symptoms on the above-ground portion of the plant. Lagging soybean yields on otherwise healthy looking plants are often the first sign of an SCN infestation.

Once you have SCN in a field, you can never get rid of it.; however, you can manage it and reduce its impact on yields. Management consists of rotating soybeans with another crop and using resistant varieties when soybeans are planted. When selecting an SCN-resistant variety, don't neglect the variety's other agronomic traits.

If you need early emergence, a good chlorosis or lodging score or phytophthora resistance, you will still need those traits in the SCN-resistant variety. Ignoring those traits and simply selecting for SCN resistance sets you up for lower yields which would likely be blamed on "SCN resistance yield drag" when it is actually caused by another factor.

The best news is that unlike other genetic resistance factors bred into seed, good-yielding SCN -resistant varieties do not cost any more than susceptible varieties.

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