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University of Illinois trials find disease presence boosts fungicide response

University of Illinois (U of I) trials in 2010
found the most profitable use of strobilurin fungicides occurred when
application was based on:

* Disease risk, such as hybrids susceptible to
disease or hybrids planted in corn-on-corn situations with reduced tillage.

* Scouting that shows disease is present on the
third leaf below the ear or higher on at least 50% of plants prior to tasseling.

“The most consistent profitable use of a fungicide
occurs when disease is targeted,” says Carl Bradley, U of I Extension plant
pathologist.

He reminds farmers that that yield response returns
need to exceed fungicide and application costs. If fungicide and application
costs hover around $25 per acre, you’d need a 5 bushel per acre yield increase
at $5 per bushel corn to break even.

However, corn prices and fungicide prices can vary.
Over time, he notes aiming for a 10 bushel per acre yield increase can better
ensure profitability. This mainly hinges on disease severity in corn. In 21 U of I test sites from
2008 to 2010, 10 bushels per acre yield spikes occurred about one-third of a
time following fungicide applications.

“When
disease severity was less than 10%, we saw just an average of .1 bushels per
acre yield response,” says Bradley. “In these cases, a 10 bushel per acre yield
responses or more occurred just 14% of the time.

Between
10% and 14% disease severity, there was an average 6.8 bushels per acre
response,” he adds. “A 10 bushel per acre yield response occurred 17% of the
time.

“At
15% or more disease severity, yield increased on average 15.4 bushels per
acre,” he adds. “Ten bushel per acre-plus yield increases spikes occurred 75%
of the time.”

Sizeable
yield increases can occur with little disease present. Fungicide application at
a Perry, Illinois, site in 2009 spiked yields 10 bushels per acre when disease
severity was well under 5%.

“There
are locations with yield spikes that do not relate to disease control,” says
Bradley. “The point, though, is how consistently they occur. Over time, yield
response is related to the diseases that are out there.”

 

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