While it’s too late to apply fungicides to soybeans with white mold symptoms, no-tillers can benefit in three ways from scouting fields before harvest, says Darren Mueller, Iowa State University plant pathologist.
First, locating hot spots of white mold may trigger management strategies to reduce the number of sclerotia for subsequent years, says Mueller, in a news release from the Iowa Soybean Association (ISA).
“If a particular field has hot spots you may want to consider burying the sclerotia that drop to the soil surface at the end of the season,” Mueller says. “Another way to reduce inoculum is to apply a biological control to kill the sclerotia.”
Second, knowing what fields are prone to getting white mold may influence what cultivar planted the next time that field is in soybeans.
“Remember those sclerotia, the small, black survival structures, can survive more than 2 years in the soil,” Mueller says.
Third, Mueller says, “You can take extra precautions to keep your combine clean of soybean stems and residue after harvesting fields with white mold. This will help prevent spreading the fungus to new fields.”
But later-planted soybeans could be treated with fungicides, Brian Lang, Iowa State University agronomist, says.
"Soybeans in the R3 stage are still within labeled recommendations for a couple of products," Lang says in his Aug. 5 Crop Notes.
"Most of the soybean crop is at the R4 stage and no longer within a treatable window with fungicides. Seeing symptoms of white mold means that the plants were infected weeks earlier and the application of a foliar fungicide for control of white mold is not recommende," Lang says.
In general, fungicides are not effective — therefore not recommended — after symptoms have developed, Mueller says.
“Fungicides are more effective if applied before disease gets established in a field," he says. "While little can be done to stop infection once the disease can be seen in the field, there still is some value in scouting.”
Soybean fields at a higher risk of white mold are those that had white mold before and are in high-yielding sites where the canopy closed early.
“Fields that have had plenty of soil moisture, high humidity and little airflow have increased chances of getting white mold,” Mueller says.
Managing white mold in soybeans is very challenging, says David Wright, ISA director of contract research and strategic initiatives.
“There are limited tools available to farmers to reduce yield loss to white mold,” Wright says.
“Applications of spray products have had varying results. Soybean checkoff investments are targeting the development of genetic resistance to white mold. We anticipate the release of breeding lines with greatly improved resistance to white mold in the next 1 to 2 years.”