Glyphosate-Resistant Kochia Confirmed
HAYS, Kansas February 26, 2010 -
Kansas State University scientists have
term evaluations of a limited number of independent Kochia (Kochia
scoparia), commonly called fireweed, 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, 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, who is 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)
lengthy evaluations of greenhouse and field studies. He, along with
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 those growers
who may have a resistance problem, but there are other herbicides
that can be used to control kochia," said Stahlman, who is based at
State´s Agricultural Research Center at Hays, Kan.
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 use of
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 noted that some
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 there is evidence that 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
there may be other kochia populations in Kansas exhibiting
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 program where possible,
including residual herbicides. It is essential that these
have good activity on the targeted species, they said.