Fifteen
states now have acres claimed by glyphosate resistant weeds.
Acres in Pennsylvania and Missouri have now
confirmed glyphosate resistant marestail populations, and
glyphosate resistant common ragweed has been confirmed in
Arkansas.
William
Curran, professor of weed science at Penn State University,
documented resistance on as much as 500 Pennsylvania acres
and Andy Kendig, associate professor for University of
Missouri Extension, acknowledged more than 10,000 acres in
the Missouri Delta. Chad Brewer, graduate student, and Bob
Scott, extension weed specialist with the University of
Arkansas, recorded as many as 50 acres with resistant common
ragweed.
In
Missouri, the first resistant population was confirmed in
2002. According to Kendig, in 2003 they were seeing a
response similar to neighboring Tennessee populations in
no-till fields. Everything in the field was controlled
except horseweed. By 2004 and 2005, Kendig’s calls on weed
escapes multiplied dramatically.
“Southeast Missouri is similar to the flatlands of Arkansas
and Mississippi in terms of tillage practices,” Kendig said.
“The horseweed has infested the majority of our cotton
fields; it is essentially everywhere. Pigweed is also a big
concern here. Residual herbicides are going to be key to
controlling these weeds.”
For
Pennsylvania, the first resistant marestail population was
confirmed in Chester County in 2003, followed by two farms
in Lehigh County in 2004. In 2005, more sites are suspected
to be confirmed. “Glyphosate resistant marestail first
appeared in fields planted with continual
glyphosate-tolerant soybeans for more than five years. We
are seeing scattered pockets of glyphosate resistance
throughout Pennsylvania,” explained Curran. “Diverse
cropping and tillage systems have prevented resistance from
becoming as widespread here as other parts of the U.S.”
Curran
agrees with other experts that rotating modes of action is
the best way to prevent resistance from developing. “We’re
recommending including 2,4-D, rotating herbicide sites of
action and using effective tankmixes to control resistant
marestail populations,” Curran said.
“We are
also watching other major weeds in Pennsylvania, such as
lambsquarters, pigweed, eastern black nightshade and yellow
nutsedge for emerging glyphosate control problems,” Curran
added. “Lambsquarters, in particular, is our biggest concern
because it is the number one weed in most crops and has
historically driven our weed control programs.”
Arkansas’s first confirmed resistant common ragweed
population was recorded in 2004, making it the second weed
in the state with glyphosate resistance. The problem field
is currently an isolated incident, originating in continuous
glyphosate-tolerant soybeans. According to Scott, giant
ragweed, Palmer pigweed and lambsquarters are also weeds to
watch for glyphosate resistance in Arkansas.
With
glyphosate resistance weed spread across 15 states, and
other states investigating problem weeds, it is more
important than ever to prolong the effectiveness of
glyphosate.
Syngenta
advocates effective resistance management with
2-1-2, no more
than two
applications of glyphosate on
one field over a
two year
period. Using products with different modes of action is
also another strategy to delay the onset of resistance. One
effective burndown is Gramoxone Inteon™ plus 2,
4-D. With its different mode of action, it allows growers to
save glyphosate applications for in-crop use. To learn more
about the Syngenta 2-1-2 program and other Resistance
Fighter™ solutions, visit resistancefighter.com
and click on the binder on the left-hand corner of the desk.
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agriculture through innovative research and technology. The
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