Glyphosate-Resistant Kochia Confirmed in Kansas
HAYS, Kan. -- Kansas State University scientists have completed long-
term evaluations of a limited number of independent kochia (Kochia
scoparia) populations on privately-owned land in western Kansas that
are now confirmed to be glyphosate-resistant. These populations have
undergone both greenhouse and field testing by K-State and Monsanto
Kochia, also called fireweed, is a drought-tolerant weed commonly
found in cropland, rangeland and pasture, and non-agricultural sites
in arid and semi-arid regions of the western United States and
Canada. Kochia is highly adaptable and grows on many soils including
saline and alkaline soils.
Phil Stahlman, a weed scientist with K-State Research and
Extension, has listed as many as five glyphosate-resistant kochia
populations in western Kansas on the International Survey of
Herbicide Resistant Weeds Web site (www.weedscience.org) following
lengthy evaluations of greenhouse and field studies. He, along with K-
State scientists Kassim Al-Khatib, Curtis Thompson, and other
colleagues, including Monsanto scientists, have investigated the
sites independently, focusing on the variability of the resistance
and difficulties in proving heritability - a trait required for
confirmation of resistance.
"This complicates and may increase control costs for growers
who may have a resistance problem, but other herbicides can be used to control kochia," said Stahlman, who is based at K-State´s Agricultural Research Center at Hays.
Thompson, who is based at K-State´s Agronomy Department in Manhattan
added, "If glyphosate-resistant kochia is suspected, the grower
should consider a two-pass weed control program that includes
residual pre-emergence herbicides that control kochia."
Kochia control can be adversely affected by both growth stage and
environmental conditions, with erratic performance fairly common.
Initially, the lack of control was thought to be due to factors or
circumstances other than resistance. Stahlman sais some growers
learned to manage kochia with glyphosate rates below the recommended
rate by using enhanced application techniques.
"We know that herbicide rate is very important in preventing
resistance and areas that practiced low use rates were among the
first to exhibit lack of control of kochia not due to environmental
factors," said Stahlman.
Monsanto is working on a multi-state effort with university
scientists in a number of Plains states to continue evaluating
standard weed management recommendations and to learn more about
glyphosate resistance in kochia.
Stahlman said evidence indicates a glyphosate-resistant kochia
population from Thomas County does not grow as well as a known
susceptible population. Thompson, however, reported a glyphosate-
resistant kochia population from Stevens County is more aggressive
than a nearby susceptible population.
Also, kochia seed viability in the soil, currently estimated at two
to three years, is being investigated by a team of university
scientists throughout central and northern Great Plains states.
Understanding more about the plant and seed characteristics across a
wide geographic region will allow greater use of other management
K-State Research and Extension personnel have received reports that
other kochia populations in Kansas may beexhibiting resistance
to glyphosate. Stahlman and Thompson advise growers to use
appropriate glyphosate rates and other herbicides with a different
mode of action in their weed control programs where possible,
including residual herbicides. It is essential that these herbicides
have good activity on the targeted species, they said.
Rick Cole, U.S. Weed Resistance Technology Development manager at
Monsanto, agrees a program approach is best: "We are working with
many university experts to provide growers with the best management
practices. To maintain the efficacy of the herbicide and value of the
technology, we recommend growers scout fields and utilize additional
modes of action that complement the Roundup Ready system to control
problem weeds while reducing the likelihood of developing performance
The company and most academics recommend growers adopt best
management practices to help growers minimize the risk of developing
resistant weeds practices including:
* Start with a clean field by either using a burndown herbicide or
tillage to control weeds early.
* Use Roundup Ready technology as the foundation of a total weed
* Add other herbicides or cultural practices where appropriate as
part of the Roundup Ready cropping system.
* Use the right herbicide rate at the right time.
* Control weeds throughout the season and reduce the weed seed bank.