Soybean sudden death
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Over the last few years, the number of fields reported with symptoms of soybean sudden death has been increasing. The first few reports of suspected soybean sudden death are trickling in, so this is a good time to review the disease symptoms and management. Soybean sudden death is caused by a fungus, Fusarium virguliforme (formerly F. solani f.s. glycines). Research shows that there is a definite relationship between soybean sudden death and the soybean cyst nematode. Although soybean cyst nematode is not required for the development of soybean sudden death, it increases its severity. Soybean cyst nematode has been found in all major soybean producing counties in Michigan. A Michigan soybean check-off supported soil testing program for soybean cyst nematode began in 1997. The percentage of soil samples testing positive for soybean cyst nematode has increased over the last few years, to about 65 percent (of an average 1100 samples per year). In fields where soybean sudden death is a problem, a combination of techniques is needed to manage both the cyst nematode and the fungus causing the disease.
Choose resistant varieties to limit yield loss. It’s important to look at both soybean cyst nematode resistance and soybean sudden death resistance levels when selecting varieties. Even when soybean cyst nematode resistant soybeans are used, soybean sudden death may be more severe in fields with a history of high levels of SCN. Because SCN is usually present in fields with SDS, it’s advisable to choose an SCN-resistant soybean that has at least moderate resistance to SDS. Growers requiring group II and shorter maturity soybeans have fewer choices for soybean sudden death resistant varieties than longer maturity groups, but there are some varieties available.
Information about SCN-resistant soybeans in the Michigan soybean variety trial ratings can be found at: http://www.css.msu.edu/varietytrials/soybean/Soybean_Home_Page.htm. Ratings of SDS resistance for commercially available soybeans has been conducted across a number of locations in Illinois for several years. That information, along with SCN ratings, maturity group and yield can be found at the Varietal Information Program for Soybeans (VIPS) websitewww.vipsoybeans.org or at the Southern Illinois University SDS North Central Soybean Research Project website, http://www.siu.edu/~soybean/.
Avoid early planting. Yield reductions due to SDS are dependent on when infections begin. Early infections result in pod abortion, reduced seed number and size. Avoid early planting, especially in soils that are cold and wet. SDS is often less severe in delayed plantings and in early maturing cultivars, as the onset of the disease doesn’t occur until later reproductive stages.
Evaluate your tillage practices. Severity of SDS tends to be greater under no-till or reduced tillage systems than conventional tillage. Reasons for this may include higher soil moisture, cooler soil temperatures and higher loads of the pathogen remaining as inoculum for subsequent soybean crops.
Improve drainage SDS is often found in wet areas or poorly drained soils.
Minimize soil compaction, wetter, less porous soils resulting from compaction favor the development of SDS.
Avoid moving infested soil from field to field on equipment or vehicles. The fungus responsible for SDS can survive for extended periods in soil.
Crop rotation is not a primary management tool for SDS because the fungus produces resting spores in the soil and can survive for extended periods in the soil, but rotating out of soybeans for at least two years does help to reduce SCN populations.
Early symptoms of SDS show up on the foliage as small, round, light green to yellow spots between the leaf veins. As the disease progresses, these spots are replaced by brown to tan areas surrounded by chlorotic tissue. Check wet or poorly drained areas of fields for plants with symptoms of SDS. A brown, grayish brown, or reddish brown discoloration shows up in the vascular (water conducting) tissues of the lower stem and root. Root systems are smaller than normal and show some degree of decay. Discoloration appears on the lower part of the taproot first. Dark blue to blue-green areas may be visible on the root surface where the pathogen has produced spores, but aren’t always present. Frequently, plants lose their leaves, but leaf petioles remain attached.
Distinguishing soybean sudden death from brown stem rot
Brown stem rot (BSR), caused by the fungus Phialophora gregata has very similar leaf symptoms. BSR causes browning of the pith, SDS does not. BSR does not cause root decay, but SDS does. BSR typically shows up later in the season (around R5-R6) than SDS.
This information, along with color photos of disease symptoms, is available as a fact sheet at: http://www.ipm.msu.edu/cat07field/pdf/7-26SDS.pdf