November 21, 2008
One management practice available for certain soybean diseases is the use of resistant soybean varieties. As you make your seed selections, consider using resistance in your soybean seed if you have one of the following problems. Always make sure to select agronomic characteristics to match your ground and conditions as well.
Soybean Cyst Nematode (SCN)
Soybean cyst nematode is spreading and has now been observed across the eastern third of Nebraska. Each year newly infested fields are identified. This disease, caused by the nematode Heterodera glycines, can be a problem anywhere, but has been found more frequently near waterways.
Once identified in a field it is critical that SCN-resistant varieties be utilized in a rotation system so that the population (number of nematodes per unit of soil) does not reach a level that makes soybean production unfeasible.
It's also important that the source of SCN resistance be rotated. This is necessary because the nematode population can adapt to the resistance source and overcome its effects.
For more information on soybean cyst nematode, including symptoms and how to sample a field, see NebGuide G1383, Soybean Cyst Nematode Biology and Management.
Phytophthora Root and Stem Rot
Phythophthora root and stem rot was a problem in many fields in 2008 as a result of wet conditions. This disease is caused by the fungus Phytophthora sojae and has been found throughout Nebraska soybean production areas. This disease is primarily a problem in fields with poor drainage or soils with high clay content that maintains high moisture levels. In many Nebraska fields, the biotypes of Phytophthora can be defeated with commonly marketed resistance genes in commercial varieties.
Several sources of resistance are sold in Nebraska: Rps 1k (most common), Rps 1c (second most common) and Rps 1a and Rps 3 (limited availability). In some cases the biotype of Phytophthora in the field may be resistant to a source and the product will be ineffective. In surveys we have identified several fields with such biotypes. In these cases it is critical that good tolerance to Phytophthora be utilized along with increased rates (high end of label range) of seed treatment fungicides containing mefenoxam.
For more information on Phytophthora, including how to identify and manage this disease, see G1785, Management of Phytophthora Root and Stem Rot of Soybeans.
Loren Giesler
Extension Plant Pathologist
