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Using Corn Fungicides in a Dry Growing Season
By
Laura Skillman
PRINCETON, Ky., (July 3, 2007) – University of Kentucky plant
pathologists say they continue to get questions on whether to
treat cornfields with a foliar fungicide as a potential yield
booster even in a dry year where disease problems are not
prevalent.
While in soybeans, there is evidence that certain strobilurin
fungicides sometimes enhance yield even when diseases are not
present at a level sufficient to affect yield, in corn, the
research base to date is much more mixed, said Paul Vincelli,
plant pathologist with the UK Cooperative Extension Service.
“Most of the studies I’ve seen, including a number conducted in
Kentucky, show no statistically significant improvement in yield
from foliar fungicides applied to corn in trials when disease
activity is minimal through grain fill,” he said. “This past
week I obtained data from a neighboring state showing some field
trials where a yield increase was observed from strobilurin
fungicides when disease activity was low. However, these studies
represent less than half of the total number of studies I’ve
reviewed.
“Furthermore, only a fraction of the total number of trials I’ve
reviewed showed yield increases that would more than pay for the
cost of the application at $4 per bushel corn prices. In those
cases where these yield increases occurred there was no common
denominator that would allow one to predict whether a field
would benefit by a fungicide application in the absence of
disease. Finally, it should be noted that the use of fungicides
for general yield enhancement, even though disease activity is
below yield-threatening levels, probably increases the risk that
fungicide resistance might eventually develop.”
These products are excellent for controlling gray leaf spot and
northern leaf blight, but incidences of these diseases are very
low this year. Dry conditions are not conducive to the
proliferation of these diseases.
According to rainfall maps at the UK Ag Weather Center, counties
west of Interstate 65 received substantial rainfall during the
past week, as did other parts of the state, Vincelli noted.
Cornfields approaching and at tasseling benefited greatly from
this rainfall, as silking is the most sensitive stage of corn to
drought. Although it is not apparent how much yield loss may
have already taken place in some fields, last week’s rains came
at a critical time for many cornfields in western Kentucky and
probably did little to “kick-start” diseases.
“If there is no disease threat at tasseling, it seems to me,
based on research I’ve done and seen from other states, that the
threat to grain fill from these diseases is low, especially if
the hybrid has some resistance,” he said. “I cannot predict what
the conditions will be for the next eight weeks, but if you are
not seeing disease at tasseling, it is likely to not be a major
factor affecting yield.”
Many questions remain about foliar fungicide use in corn,
Vincelli said. But his best assessment is that routine spraying
of cornfields doesn’t look advantageous for this year. Some
fields might benefit, however, depending on how many of the risk
factors are present. Risk factors include high-value specialty
corn production, disease-favorable weather, disease activity at
tasseling, irrigation, high yield potential, late planting,
no-till production, continuous corn production and susceptible
hybrids.
“If I were a producer planning to spray, I would try to arrange
to leave one or more untreated strips,” he said. “An
unreplicated, untreated strip is not a valid experiment, but at
least it would give the producer a crude indication as to
whether they might have gotten some benefit from the
application. Even crude information is better than no
information, and no information is what the producer will have
if he treats the entire field and leaves nothing untreated.
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Contact: Paul Vincelli, 859-257-7445, ext. 80722
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