Monitoring Soybean Diseases
By Katie Drewitz, University of Minnesota Extension
PRESTON and CALEDONIA, Minn. (08/23/2022) — As summer and the growing season wind down our management window is closing. However, scouting your crops is still important to ensure informed management decisions. Soybean fields with White Mold and Sudden Death Syndrome are becoming quite apparent even from a distance. By recording locations and spread of these issues you can tell whether your disease management is being effective or if it is time to try something new. Below are some simple descriptions and management tools for you to consider when planning for next season.
White Mold: White mold is identified by fluffy white growth on soybean stems. Initial symptoms develop from R3 to R6 as gray to white lesions at the nodes, which is followed by white fluffy mold covering the infected area. Black sclerotia soon develop and are visible within the mold on the stem lesions and inside the stem as the plant approaches death. Pods affected by white mold are typically smaller, lighter, and fuzzy. The fungus may survive in the soil for several years, making management of this disease a long term issue. Management for white mold includes selecting varieties with known resistance to white mold, rotation to a non-host crop, no-tillage, late planting, wide row widths, and lower plant populations. Tradeoffs for using these practices include reduced weed management efficacy and reduced yield potential. However if white mold issues are great enough these tradeoffs may be worth the risk. Also remember that many broadleaf weeds are hosts for white mold and some herbicides may help suppress the fungus. For white mold issues that do not respond to the above options, foliar fungicides and biological options may need to be considered. When looking at those options, consider the cost of application, application timing, and chemicals used to help maximize the effectiveness and return on investment.
Sudden Death Syndrome (SDS): SDS is identified by scattered interveinal yellow chlorotic blotches that eventually progress into large irregular patches. These patches typically are brown lesions surrounded by yellow chlorotic tissue. Eventually leaves may detach from the petioles, leaving the petioles attached. Brown stem rot and SDS may be confused with each other as leaf damage can look quite similar. However, SDS will also cause root rot and the pith of the stem will remain white where brown stem rot will cause the pith to turn brown. Management of SDS includes planting soybean varieties that are resistant to SDS and soybean cyst nematode, reducing excessive soil moisture with drainage, minimizing compaction, crop rotation, and planting into warmer soils.
While we are past the point of management for this growing season, it is important to note if and where you are having these issues. Making notes now will help you to be more informed when making variety decisions this fall and determining your field rotations. For more information on these diseases please visit www.extension.umn.edu and type “Sudden Death Syndrome” or “White Mold” into the search box.