Early Season Hail Damage And Corn Diseases
LEXINGTON, KY.
Although rain has been
scarce in many areas of
Western Kentucky, some
areas that have received rain
have reportedly suffered hail
injury. Some concern has
been expressed about the impact
of that hail damage on
diseases. In general, I don’t
expect much increase in disease from hail damage
at this stage of the growing season, but
there are a few things to consider.
Bacterial diseases are favored by wounding.
Thus, hail damage could increase damage from
Stewart’s wilt, a common bacterial disease of
corn. The mild winter favored overwintering of
the corn flea beetle. This is important, because
this is where the Stewart’s wilt bacterium overwinters.
The flea beetle also is the vector of this
bacterium, so more beetles means more risk.
However, Stewart’s wilt is generally found at
very low levels in Kentucky field corn, because
of breeding for resistance. So while I would be
watchful for it, I don’t expect major problems to
develop, in spite of hail damage.
Goss’s wilt is another systemic bacterial disease
of corn which could possibly be enhanced
from hail damage. While the disease has spread
to the Corn Belt in recent years, it has not yet
been detected in Kentucky. If it actually is present
at low levels in the state, hail damage could
cause an increase in disease activity, but I think
this is a low risk presently. Neither Goss’s wilt
nor Stewart’s wilt are controlled by fungicides.
As far as fungal diseases, the principle diseases
targeted by fungicides – gray leaf spot,
northern leaf blight, and rusts – are not substantially
favored by wounding. Infection by
rust fungi would be lessened by wounding,
since those fungi only infect healthy, live tissues.
The gray leaf spot fungus penetrates the
plant through microscopic stomates, so wounding
probably does not favor that process, because
it tears up intact leaf tissue. To my
knowledge, infection by northern leaf blight is
not significantly increased by wounding, either.
Hail kills leaf tissue, and that necrotic tissue
may serve as a food base for spore production
by northern leaf blight, resulting in increased
sporulation. However, that effect probably
would be modest.
Supplementary labels of certain strobilurin
fungicides may recommend their use to enhance
crop tolerance to the effects of hail damage.
However, the only critical studies of this
phenomenon (from the University of Illinois)
have shown no enhanced tolerance to simulated
hail damage from a fungicide application applied
at VT.
Summary
While I don’t expect widespread problems,
corn fields damaged by hail in the past few
weeks should be monitored for the possibility of
increased disease. At this stage, I know of no
evidence that would support the application of
fungicides on hail-damaged fields, unless those
fields are already under a substantial risk of
disease (for example, a susceptible hybrid under
no-till, continuous corn). Δ
DR. PAUL VINCELLI: Extension Professor and
Provost’s Distinguished Service, University of
Kentucky