Be on the watch for Sudden Death Syndrome (SDS) this season. Conditions have been right so far for an outbreak.
SDS is a serious disease in soybeans and impacts soybean production across the U.S. It is probably No. 2 after soybean cyst nematode in causing a yield decline. And 2014 could be a high-risk year.
It has been very wet throughout much of Illinois this season. Wet soils mean wet feet for soybean plants (i.e., roots are growing in saturated conditions). Many growers saw yellowing in their soybean fields in June. Wet feet may lead to an increase in soybean diseases or a reduction in nitrogen fixation. Diseases that occur in the summer under wet conditions include SDS and brown stem rot (BSR).
SDS is a soilborne disease that causes leaf death and root rot. It doesn’t occur each year, and it takes the right set of environment conditions in the spring and summer for the disease to develop. The fungus produces a toxin that translocates from the infected taproot to the leaves and causes the dying of leaf tissues and eventually the above-ground plant.
Though symptoms are first seen on the leaves at midsummer, the infection begins back at emergence and seedling stages when the pathogen infects young roots. Visual symptoms aren’t evident until later in the summer when the pathogen begins to flourish in the plant and produce a toxin.
The symptoms of SDS are small, light-green to yellow spots on soybean leaves, closely followed by “mosaic-like” symptoms on the uppermost leaves, which eventually turn brown, become necrotic and fall off the plant. These symptoms are generally seen midsummer or later when the plants are flowering and filling pods.
SDS is a difficult disease to manage. Growers can select varieties that are tolerant to SDS, plant at the right time and manage the crop to minimize crop stresses.
- Follow recommended planting dates and avoid early planting. Planting a bit later in the middle to the end of the recommended planting window should be considered in fields with a SDS history.
- Improve field drainage and reduce soil compaction. Remember, soybeans don’t like wet feet—wet areas easily become compacted, and compacted areas stay wetter as soil drainage is impeded. Soybean roots in wet areas fare badly in the presence of the SDS fungus.
- Evaluate the tillage system—studies have shown that no-till systems result in much higher percentages of SDS-infected leaves than disking or cultivating. However, some growers that use aeration forms of vertical tillage have discovered that aeration dries the soil more quickly, helping to prevent these early-season infections.
- Reduce stresses—these include herbicide stress, nutrient deficiencies, low pH and the presence of SCN. The healthier the plant, the better it can resist any disease encroachment.
While it is still too early to know for sure if we are going to see a major SDS outbreak in Illinois, if July remains moist and warm after a wet spring, the chances are pretty high it will show up, especially in fields that have a prior history.
Keep a watchful eye on soybeans planted in high-risk fields that have a history of SDS.
Agronomist Dr. Daniel Davidson posts blogs on agronomy-related topics. Feel free to contact him at firstname.lastname@example.org