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Where Fall Herbicide Applications May Fit

If
your fields this fall look like a salad bowl of weeds, you may be considering a
fall herbicide application. That’s particularly true if your fields were overrun
by marestail this year.

“We really lost the battle on marestail this year,”
says Bill Johnson, Purdue University Extension weeds specialist. “We have had
glyphosate-resistant marestail for a decade, but this year was a complete train
wreck.”

Marestail is a versatile weed, as it can double both
as a fall and summer annual. That was the case for the marestail that infested
Indiana fields during the 2012 growing season.

“We had both a spring- and fall-emerging population,”
says Johnson. “Typically in the fall, 80% of (marestail) plants die due to
winterkill. Last winter, we didn’t have any winterkill. Those plants made it
through the winter, and they quickly grew too large for spring burndown
applications to kill.”

Typically,
Mike Owen, Iowa State University Extension weed specialist, doesn’t recommend
fall herbicide applications.

“Applying
a herbicide in the fall hoping that it will deliver residual control (into
spring) is a crapshoot,” he says. “If you have an early wet spring, you might
lose some of that control next spring. In instances where planting is delayed,
you may not have any residual at all.”

There’s
one exception, though. “If you’re looking to control winter annuals this fall,
they can make good sense,” says Owen.

Fall
applications can curb marestail populations that take the winter annual route. However,
Owen adds that much of the marestail in Iowa behaves more like a summer annual
than winter annual and germinates in April and May.

Johnson says Indiana farmers may need to start
thinking like farmers in Tennessee who have wrestled with massive flushes of
glyphosate-resistant marestail.

“Some of those farmers put down two burndown
treatments—one early in the spring and another at planting,” says. “If not,
they lose the battle with marestail.”

 

 

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