With moderate temperatures and ample rainfall for many growers providing near ideal conditions
for crop growth, these same conditions are also providing the necessary environment for the rapid
development of Soybean White Mold.
Sclerotinia White Mold or White Mold is a disease which thrives under moist and cool environment
(less than 84 degrees) and where soybeans have developed a thick, dense canopy.
The mold itself results from spores which are released from fruiting apothecia found on the soil
surface and resemble small clay pots.
The spores enter the soybean plant through blossoms and quickly develop within the stems of soybeans
and produce small black chunks called sclerotia. The White Mold fungus quickly starts to restrict
water and nutrient flow to upper stems and leaves resulting in dead tissue and pods. Infected plants
will exhibit dying leave and pods on the upper part of the plant and looking lower into the canopy,
one can see the fuzzy white growth of the fungus itself. Unfortunately very little can be done when
plants have become infected and yield and grain quality can be drastically reduced.
The single best way to combat White Mold is to begin planning early on by selecting varieties with
highest White Mold rating as possible. Fields with a history of manure or other high yield environments
can be planted to wider rows to allow more air flow or in some cases planted later to reduce the height
of the plants.
Lowering the plant population is another option but still does not guarantee the severity of the disease
will be lessened.
Finally crop rotation may help as the sclerotia will germinate and produce spores and lacking a suitable
host will not reproduce. Unfortunately there are a large number of host plants such as ragweed, pigweed,
lambsquarters and velvetleaf, along with most bean crops that will support White Mold. Even a seven year
continuous corn field near Galesburg IL had fruiting bodies present and with the number of blossoms present
could very easily infect these fields.
A fungicide treatment like Domark may be an option, but fungicides must be applied before any sign of
spore activity is present to have some level of control.
Tillage affects the survival of white mold, but there are no good recommendations for disease management
because of this disease's unique features. Sclerotia can survive in deep soil up to seven years. Only
sclerotia within 2 inches of the soil surface can germinate and release spores to infect soybeans. Burying
infested residues by mold-board plow can prevent germination of the sclerotia. But the effectiveness in
controlling white mold by burying sclerotia is affected by cultivation and tillage in following seasons.
For example, if you cultivate, disk, or use a chisel plow in corn the following season, you bring some
sclerotia to the soil surface. Further, if soybean fields have already been infested by white mold in past
seasons, the sclerotia may be mixed in the soil. Fall tillage of these fields would bury new sclerotia in
deep soil, but uncover old sclerotia.
Growers in Wisconsin and Minnesota have been exposed to White Mold for years and have adapted their practices
to alleviate some of the potential yield losses associated with White Mold. Growers who have not experienced
need not to panic, but to plan early and smart to deal with this disease.
Click the thumbnail images below to see full size picture that show the progress of the disease from the mold
emerging on the stem, to sporadic plants dying in the field to the sclerotia in the stem that will be the
White Mold vector in the soil for future infections.