April 17, 2015
The old saying goes, "April showers, bring May flowers" but do you know what a May flower brings? Keep reading to find the answer!
Recent rains and weather patterns have changed plans for many farmers. Besides keeping folks out of the field because it's too wet, these conditions also have lowered soil temperatures from the low to mid-50's a couple weeks ago to mid- to upper 40's late last week across northeast Nebraska. The rain was a welcome blessing for some while others are saying enough for now.
One thing you might not associate with cool wet soils this spring is an increased chance of having sudden death syndrome (SDS) or brown stem rot (BSR) in soybeans. Both these diseases show foliar symptoms later this summer. However, the initial infection takes place in the spring
Both diseases survive in the soil and enter the plant and infect the roots in the spring. Symptoms don't appear until later in the summer when rains or irrigation around flowering time flush a toxin, formed by the infection in the roots, up to the leaves, creating the foliar symptoms.
It will help you manage this disease if you remember that it starts with an infection in the roots in the spring. So if you've had problems with sudden death syndrome or brown stem rot in the past, you should be aware that the cool, wet soil conditions we're currently experiencing are favorable for disease development this spring. Besides cool, wet conditions, compaction and high yield environments also favor disease development.
Another contributing factor to these diseases is soybean cyst nematodes or SCN. Sometimes it causes some confusion so I want to be clear, you can have either SDS or BSR and no SCN in your field, or you can have SCN in your field and no SDS or BSR. However, if you do have SCN in your field, your are more likely to have either of these diseases. That's because SCN causes microscopic injuries to the root when it feeds that create sites where either of these diseases can easily enter and infect the root.
So if you have pockets of either of these diseases in your fields, it might 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 50 yards or so into the healthy looking soybeans. Often the level of SCN infestation will be higher in the diseased areas. Bags for a free SCN analysis, funded by the Nebraska Soybean Board, are available at your local Nebraska Extension office.
The first step in controlling either of these diseases is selecting the right soybean varieties because there is genetic resistance for both of these diseases. 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 of these diseases, consider rotating away from soybeans for two or three years if that will fit in your operation. If that won't fit your operation, or if the incidence of either of these diseases was light to moderate in the past, consider planting these fields last so the soil has had a chance to warm which will reduce the likelihood of either of these diseases.
Also, do not do tillage in wet fields in an attempt to "open up" the soil or dry them out. Rather than improve the situation, you are likely to cause compaction which will actually increase, rather than decrease, the probability of either of these diseases.
In the past, seed or foliar fungicide treatments have not been effective in controlling either of these diseases. In 2015, Bayer Crop Science is launching a new seed treatment, ILeVO, which has shown some promise in fields with sudden death syndrome.
For more information on either of these diseases, contact your local Nebraska Extension office. Oh, and the answer to the earlier question... you should have paid more attention in your grade school history class and you would know that a Mayflower brings Pilgrims! OK, that was pretty bad! You can quit reading now and I'm going to get back to work since this comic thing isn't working out!