Diplodia Ear Rot Causing Problems In Corn Across The State
URBANA, ILL.
Diplodia ear rot, caused
by the fungus Stenocarpella
maydis (formerly
Diplodia maydis), has
been widespread in corn in
Illinois this year. Reports have
indicated that several fields
are affected and that some
may have incidence as high as
70 percent. Other ear rots
have been reported, but
Diplodia is apparently affecting the most acres
this year. The high levels of infection being observed
are a result of the frequent rainfall just
before and throughout silking;
ears are most susceptible to Diplodia
from silking to approximately
3 weeks later.
Symptoms of Diplodia ear rot.
Ears affected by Diplodia may
have a white mold growing on
and/or between the rows of corn.
Ears affected within two weeks
after silking may be completely
“mummified,” while in later infections
a light, cottony growth may
be observed growing on the ear.
Speck-sized fruiting bodies (pycnidia)
will be formed by the Diplodia
ear rot fungus and often can be
observed on the sides of the kernels.
Symptoms of Diplodia ear rot. Black specks on kernels are
fruiting bodies (pycnidia) produced
by the Diplodia ear rot fungus.
What types of loss will be incurred?
Kernels affected by Diplodia
ear rot will be light, so overall
test weight can be reduced. In
fields with high levels of ear rot,
discounts applied at the elevator
can be expected for the presence
of damaged kernels. In severe
cases, the cob may also be rotted, which means
that pieces of the cob will not separate well from
the grain. In these cases, additional discounts
for presence of foreign material may also be applied.
In the U.S., the Diplodia ear rot fungus is
not known to produce any mycotoxins, but
other fungi may colonize affected ears and kernels,
and some of these, like Fusarium, may
produce mycotoxins.
I have Diplodia ear rot – what do I do now? To
prevent additional fungal growth and disease
spread within ears, it is best to harvest affected
fields as soon as possible and to dry the grain to
below 18 percent moisture (or below 15 percent
for long-term storage). If you have crop insurance,
contact your agent as soon as possible, as
specific documentation may be needed for a
claim to be filed. Despite the fact that the Diplodia
ear rot fungus is not known to produce any
mycotoxins in the U.S., moldy grain should always
be tested before being fed to livestock. In
Illinois, grain can be tested for the presence of
mycotoxins at the Department of Agriculture’s
Centralia Animal Disease Laboratory.
How can I prevent Diplodia ear rot next year?
The first step in managing Diplodia ear rot is to
choose hybrids with better resistance. In a year
with severe Diplodia ear rot like 2009, seed
companies and growers should be able to identify
hybrids to be avoided and those that appear
to resist Diplodia a little better. Seed companies
generally provide ratings of their hybrids for
susceptibility to Diplodia ear rot. For 2010,
avoid planting corn back into fields that had severe
Diplodia ear rot in 2009. Although the days
of the moldboard plow are gone, burying corn
residue affected by Diplodia is one way to manage
the inoculum levels that may be present
next year. However, one must balance between
tilling for disease management and leaving
residue to help prevent soil erosion. Foliar
fungicides should have very little effect, if any,
on Diplodia ear rot, and it is important to note
that none of the foliar fungicides registered for
use on corn has Diplodia ear rot on the label. Δ
CARL BRADLEY: Extension Plant Pathologist,
University of Illinois