In the News - March 2008
Glyphosate-resistant Johnsongrass found in Crittenden County field
LONOKE, Ark. - Glyphosate-resistant Johnsongrass has been confirmed in a
Crittenden County field, said Dr. Bob Scott, a University of Arkansas Division
of Agriculture Extension crop, soil and environmental science specialist, adding
that so far, it’s the only known population in Arkansas.
The discovery is important because glyphosate, also known as Roundup, has
been a longtime weed control ally for farmers. It has been effective on
Johnsongrass, which is a tough customer for producers. Johnsongrass is a very
efficient weed - it can grow from both seed and root-like rhizomes.
Scott said it’s important to note that the resistance is to field application
levels of the herbicide.
The story began last year.
"The farmer approached the county extension agent about this weed he couldn’t
kill," Scott said. "County agents Jason Osborne and Mike Hamilton went out and
did some investigating on their own and believed there might be more to it then
just control failures, so they contacted me."
Back in the fall, Scott took Johnsongrass samples back to his laboratory for
a closer look.
"We have a nice facility at Lonoke for doing this kind of work," he said.
"We tested both rhizomes and seed and both were resistant," Scott said. "We
need to do further testing to determine the extent of the resistance and
probably need to do other studies on heritability and distribution."
Scott added, "We have also determined that this bio-type is not resistant to
Select herbicide, so at least we have an alternative option."
The bad news for farmers is that "by testing both the rhizome and seed, we
have determined it is a heritable trait," Scott said.
The next step is to confirm the lab findings in the field.
"We’ll go out and spray some to confirm it," Scott said.
The discovery of the Johnsongrass brings to five the number of glyphosate
resistant weeds found in Arkansas. The others are: horseweed, common ragweed,
giant ragweed, and Palmer amaranth, also known as Palmer pigweed.
Resistant Johnsongrass also was discovered this past fall, across the
Mississippi River in a field near Clarksdale, Miss., by Monsanto, maker of
Roundup.
For more information about weed control, contact your county extension office
or visit www.uaex.edu. The Cooperative Extension Service is
part of the U of A Division of Agriculture.
March 14, 2008
Media Contact: Lamar James
Extension Communications Specialist
U of A Division of Agriculture
Cooperative Extension Service
(501) 671-2187 or (501) 753-0207
ljames@uaex.edu
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