Virgil Schmitt, Extension Field Agronomist and Daren Mueller, Department of Plant Pathology
White mold has become evident in soybeans during the last two weeks, especially in eastern Iowa. Although infection occurred shortly after the beginning of flowering in late June and early July, the characteristic white myecial growth on infected plants has only become apparent the past two weeks. Really the only good news about this disease is that it does not have too much of a secondary disease cycle. In other words the disease itself is no longer spreading or is spreading one plant at a time.
The availability of fungicides for soybeans has raised many questions about their efficacy against white mold, particularly at this stage in the development of the disease. Despite some of the fungicides being classified as "curative", there most likely will be little positive effect from any fungicide applied at this time because of the stage of the disease. Remember that "curative" fungicides do NOT cure the plant of disease.
The most important thing for growers to do at this time is to note the presence of white mold in the field and then select for varieties with lower susceptibility or higher tolerance for white mold the next time soybeans are grown in the field. Wider rows may help with white mold, but wide rows have other drawbacks. If the conditions are good for white mold infection (cold and wet) at the beginning of flowering, the application of an appropriate fungicide at that time may help. An application of Cobra at or just before the first bloom has also been shown to lessen the impact of white mold.
Virgil Schmitt is an extension field agronomist serving eastern Iowa. Schmitt can be reached at (563) 263-5701 or by email at firstname.lastname@example.org. Daren Mueller is an extension specialist with responsibilities in the Corn and Soybean Initiative. Mueller can be reached at (515) 460-8000 or by email at email@example.com.