Sudden Death Syndrome and Brown Stem Rot Infections Start in Spring
Cool wet soils in spring can lead to increased chances for sudden death syndrome (SDS) or brown stem rot (BSR) in soybeans. While foliar symptoms for both of these diseases won't appear until later this summer, initial infection occurs in the spring. Later in the summer rains or irrigation around flowering time flush a toxin, formed by the infection in the roots, up to the leaves, creating the foliar symptoms.
If you've had problems with sudden death syndrome or brown stem rot in the past, you should be aware that cool, wet soil conditions are favorable for disease development in spring. Compaction, high yield environments, and having soybean cyst nematodes (SCN) are other factors favorable to disease development.A field can have either SDS or BSR and not have SCN, or it can have SCN and not have SDS or BSR. However, if a field has SCN, the likelihood of an SDS or BSR infection increases. That's because when SCN feeds, it causes microscopic injuries to the root that create sites where either of these diseases can easily enter and infect the root.
If you have pockets of either of these diseases, it would be good to pull a soil sample to test for SCN. Take one sample from the areas where the disease is present and another sample about 50 yards into healthy soybeans. Often the level of SCN infestation will be higher in the diseased areas. Samples can be submitted to the UNL Plant and Pest Diagnostic Clinic in Lincoln for diagnosis. Bags for free SCN analyses, funded by the Nebraska Soybean Board, are available at your local Nebraska Extension office.
Managing Sudden Death Syndrome and Brown Stem Rot
The first step in controlling either SDS or BSR is selecting a soybean variety with genetic resistance. Visit with your seed dealer about varieties with resistance or tolerance to SDS or BSR. Remember, a variety may be resistant to one disease or the other, but not both, so it is important to know which disease is present in your field. This is particularly important and a little tricky because the symptoms of both diseases are very similar. If you have SCN in your field, also select a soybean variety with good SCN resistance.
If you have fields with a history of being severely affected by either SDS or BSR, consider rotating away from soybeans for two or three years. If that won't fit your operation, or if the incidence of either of these diseases has been light to moderate in the past, consider planting these fields last so the soil has a chance to warm. This will reduce the likelihood of these diseases developing.
Also, do not do tillage in wet fields in an attempt to "open up" the soil or dry it out. Rather than improve the situation, you are likely to cause compaction which will actually increase the probability of either of these diseases developing.
In the past, seed or foliar fungicide treatments have not been effective in controlling SDS or BSR. In 2015, Bayer Crop Science is launching a new seed treatment, ILeVO®, which has shown some promise in fields with sudden death syndrome.