by Glen Arnold, Putnam County
In the past few weeks many local soybean fields have shown symptoms of a disease first found in Ohio less than ten years ago called Sudden Death Syndrome (SDS). The disease was discovered in Indianain 1986 and is thought to have originated in Missouri in the early 1970’s.
Foliar symptoms of SDS may appear anytime from bloom to pod fill, although symptoms usually appear between the R3 and R6 growth stages. Symptoms begin as small, bright, pale green to yellow circular spots on the leaves.
As the disease progresses, brown to tan areas surrounded by chlorotic tissue develop in between the veins. The veins of the leaves remain green much longer than the tissue between the veins. Usually the upper leaves are affected first. The pith of affected plants is white. The classic foliar symptoms of SDS only last about 2 weeks and then the infected plants look like any other dead soybean plants.
Soybean plants with SDS also have substantial amounts of root decay and discoloration of roots and crown. Yield reductions due to SDS are dependent on when infections begin. Typically infections that occur after flowering will not have a significant impact on yield. Infections that occur early will result in pod abortion, reduced seed number and size. Usually the most productive part of a field is affected.
There have been numerous studies in the past 10 years to determine which environmental factors favor SDS development as well as interactions with soybean cyst nematode. Some of the factors that favor disease development include high soil moisture during the vegetative growth period and unseasonably cool temperatures prior to or during flowering and pod set.
The association of SDS with soybean cyst nematode has not been as clear cut. Several studies and field observations indicate that soybean cyst nematode is not necessary for infection, but that its presence can increase the severity of the foliar symptoms.
Farmers wanting to see the white female soybean cysts can do so now by carefully digging up soybean roots and looking at the small hair roots. The cysts have to be kept moist for easy viewing.
Companies and Universities are beginning to rate soybean varieties for resistance to SDS. Farmers planting soybean into fields with a history of SDS next season should ask for this information.
More information and a photo of SDS in soybeans can be found at this Ohio Agricultural Research and Development Center website http://www.oardc.ohio-state.edu/ohiofieldcropdisease/