Issue No. 18, Article 3/July 23, 2004
Sudden Death Syndrome of Soybean Appearing in Illinois
Sudden death syndrome (SDS) has been observed in the past week in central and southern Illinois soybean fields. As usual, the symptoms often begin to appear in late July or early August in Illinois, usually while soybean is flowering. It is difficult to predict when, where, and how severe SDS will be because of the many environmental and other factors that influence its development. Conditions seem to have been favorable for development of SDS in some, if not many, areas of Illinois.
The following list gives some of the conditions that seem to favor development of SDS. (I'm sure that many of you who have dealt with this disease in the field could add to the list.)
- Early planting--the date for this varies from north to south in Illinois
- Compacted soil, poor drainage
- Wet soil conditions after planting
- Soybean cultivars with below-average ratings for SDS resistance
- Environments favorable for high soybean yields
- High populations of soybean cyst nematode (SCN)
- Heavy rainfalls occasionally throughout summer
To date, reports of SDS have come from these counties: Champaign, Montgomery, Schuyler (several fields), and Wayne (two reports). SDS is certainly spread more widely than these counties alone, but these reports indicate that the disease is not currently restricted to one area. The conditions in an area where SDS was reported in Montgomery County show a common trend of where SDS occurs: the field was planted early, the soybean variety had a below-average SDS resistance rating, there was heavy rainfall after planting, and the field was wet for 3 weeks after planting.
Symptoms of SDS can be found on the roots and leaves. The foliar symptoms of SDS are most obvious. Chlorotic spots develop between the veins on leaves, and the leaves may become cupped or curled. The spots typically enlarge to become brown lesions surrounded by yellow areas. The leaves often detach from the petioles as the disease progresses. The foliar symptoms can appear very similar to symptoms of brown stem rot (BSR), but the pith remains white in plants infected with SDS, whereas the pith becomes brown, especially at the nodes, in plants infected with BSR.
Root rot symptoms of SDS are not as obvious, but they are important in the development of this disease. Root rot may develop and plants may then be pulled easily from the ground. Sometimes a blue fungal growth develops on infected roots, especially in moist soils. Gray-brown discoloration can develop inside the root and in the vascular tissues of the lower stem.
Early stage symptoms of sudden death syndrome (SDS) on soybean.
Symptoms of SDS on soybean leaves.
In a sense, SDS, which is caused by the soilborne fungal pathogen Fusarium solani f.sp. glycines, has two phases. It infects through the roots, and the infection can move up the roots into the stem. Thus, this pathogen can cause root rot, and yield loss can result from root rot alone in the absence of severe foliar symptoms. In addition, the SDS pathogen also produces a toxin, which is translocated up the plant and is a primary cause of the foliar symptoms.
SDS remains difficult to manage. The key to reducing yield losses from SDS is to plant cultivars with relatively high levels of tolerance or partial resistance to SDS. Information on SDS tolerance/resistance for commercial varieties from trials in Illinois can be found at the VIPS (UIUC) Web site and the SDS/SCN Web site (SIUC). In addition, it may be beneficial to plant later than normal where SDS has been a problem, improve soil drainage if possible, and plant SCN-resistant cultivars. Deep tillage may help to reduce disease severity in some compacted areas. Crop rotation has not shown consistent benefits for SDS management.--Dean Malvick