Early Season Fungicide Applications On Corn
LEXINGTON, KY.
With respect to fungicides
on corn, research
at land-grant
universities typically supports
two conclusions, discussed
below.
The most sensible use of
fungicides is in fields with
the highest disease risk.
Fungicides sometimes improve crop productivity,
and sometimes not. Independent research
pretty commonly shows that the best predictor
of benefit is, how much is the risk of foliar fungal
diseases like gray leaf spot? I’ve discussed
this in numerous articles previously, as have
other university-based corn pathologists.
If using a fungicide, the greatest benefit
usually comes from a single application at
tasseling (VT) through silking (R1). In the
past couple of years, there have been marketing
efforts promoting the use of fungicides on
early-stage corn (V4 to V8). The advantage of
applying fungicide this early is that it may be
tank-mixed with herbicide. This eliminates the
extra application cost of a fungicide application
at VT/R1. The problem with the early applications
is that, in general, they don’t provide as
much benefit, compared to a VT/R1 application.
The table top right provides selected example
data from a much larger trial conducted by
Kiersten Wise, Purdue University (published in
Plant Disease Management Reports, 4:FC092).
Overall results for numerous university trials
throughout the Corn Belt in 2010 are presented
in the table bottom right (summary data
provided by Kiersten Wise).
It is very clear from these data that, if you
must use a fungicide, an early application is
not as good as at VT/R1. Fungicide application
in the V4-V8 window often results in a loss
of disease control, compared to fungicide application
at VT/R1. This makes sense, because
diseases like gray leaf spot accelerate during
grain fill, and a V6 application can “run out of
gas” by the time the disease really gets going.
Furthermore, research indicates that dual applications
may often be uneconomical.
Bottom line: The public research thus far
doesn’t provide a good reason to make an early
season application of fungicide to corn. If you
are considering using a fungicide,
1. Direct it to fields with greatest risk of gray
leaf spot and other leaf diseases.
2. Apply it between tasseling and the time
when silks begin to turn brown. Δ
DR. PAUL VINCELLI: Extension Professor Plant
Pathology, University of Kentucky