Lexington, kentucky
March 18, 2009
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.
UK College of Agriculture, through its land-grant mission,
reaches across the commonwealth with teaching, research and
extension to enhance the lives of Kentuckians. |
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