UK Specialists Question Fungicide Use For Stress Tolerance
LEXINGTON, KY.
Certain fungicides are highly effective at controlling
several diseases in grain crops. But
recently, these fungicides have also been
marketed for stress tolerance and growth efficiency
purposes.
University of Kentucky specialists are hesitant
to recommend fungicides for anything other
than disease prevention, because they have not
seen research-based field data to prove these
products provide added benefits to Kentucky’s
grain crops.
Paul Vincelli, extension professor of plant
pathology in the UK College of Agriculture, Don
Hershman, also a UK extension professor of
plant pathology, and UK Grains Crop Specialist
Chad Lee have conducted fungicide studies
since 2003 on soybeans and, since 2007, on
corn to determine their effectiveness in Kentucky’s
fields.
“We are not saying these claims are not true;
it’s just that we have not seen convincing proof
that they are,” Vincelli said. “Most university research
conducted to date does not support these
claims.”
The specialists said this is an issue producers
need to be aware of going into the growing season.
One company has received U.S. Environmental
Protection Agency approval for a
supplemental label allowing fungicide use for
purposes in addition to disease control, and
other companies may follow suit.
While fungicides are ideal for controlling foliar
fungal diseases, historically, Kentucky corn and
soybeans are not grown under conditions that
favor much disease development.
“If conditions favor disease development, then
fungicides are beneficial, but the current evidence
does not warrant blanket applications of
fungicides,” Lee said.
Hershman has conducted 28 studies of modern
fungicides on soybean yields. In the studies,
fungicides were applied during the early pod (R3)
stage, which is the target application time.
Yields varied from a loss of 3 bushels per acre to
a gain of 26 bushels per acre. Yield increases occurred
about 25 percent of the time, but those
increases could not be traced back directly to
fungicide control of visible diseases.
However, this is not scientific proof that the
yield increases were due to fungicides enhancing
stress tolerance or generally improving growth
efficiency. Hershman said it is more likely the
yield increases were the result of the fungicides
controlling diseases that were not easily observed
or disease complexes which are not fully
understood.
Vincelli and Lee have conducted similar studies
in corn during the past two growing seasons.
During their studies, the fungicides were applied
during the corn’s target application stages, between
full tassel and brown silk (VT through R1).
In their studies, there have been no significant
yield increases between treated and untreated
plots when there was a low level for disease. Vincelli
said many universities conducted studies
on corn across the Midwest and beyond, and few
showed significant yield increases in fields with
little to no disease activity.
Farmers could incur additional economic risk
if they decide to apply fungicides for improved
growth efficiency or stress tolerance. Lee said if
there’s not a yield increase, farmers will not recoup
the application cost. He added that even
with modest yield increases, farmers may not recoup
the application cost. In 2007 and 2008
university studies, the cost was recouped in
corn only about 38 percent of the time. One industry
study showed that soybean farmers were
able to recoup their costs about 51 percent of
the time.
Unnecessary fungicide applications could have
some adverse effects, the specialists said. If
fungicides are tank-mixed with other products
and applied at the wrong development stage, it
can hurt yields. Other effects may include increased
environmental risks, increased development
of fungicide-resistant diseases, occasional
surges in insect and mite populations, and a
loss of time and money.
Looks can be deceiving, the specialists emphasized.
Treated crops sometimes look greener
than those that are not treated. While this
“greening effect” is visually pleasing, it can have
some negative consequences including slow or
delayed harvests and the necessity to dry grain.
The UK specialists noted that, in their studies,
many times treated corn plots would look
greener, but there was no significant yield increase
compared to untreated plots. Similarly,
treated soybean crops frequently look cleaner
than non-treated crops, but this too is often not
associated with higher yields.
The specialists caution growers against applying
fungicides to crops that have a low risk of
disease until more convincing data is available.
If producers decide to treat crops with a fungicide
application this year, they recommend
growers leave untreated strips to determine the
fungicide’s biological and economical effects.
Producers should treat the crops during the
proper development stages. Producers should
follow label instructions exactly and make sure
they have excellent spray coverage on treated
crops. Those who have questions or would like
more information on fungicides and their uses
should contact the local county office of the UK
Cooperative Extension Service. Δ