Weed Science Update
Colorado Wheat Field Tours
The Weed Science group at Colorado State University participated in the Colorado
Wheat Field Days during June, 2003. Information was provided to area farmers
on new herbicides and their use in winter wheat. Greatest interest was generated
when the discussion focused on CLEARFIELD* Wheat. CLEARFIELD* Wheat variety ‘Above’ was
developed by BASF and Colorado State University. Above is the first imidazolinone
tolerant wheat line introduced into the winter wheat market. Above wheat is used
in combination with Beyond herbicide. Beyond herbicide provides selective control
of winter annual grasses such as downy brome, jointed goatgrass, and feral rye.
Time of application on feral rye is critical in order to achieve optimum weed
control. Recommendations are to treat feral rye in the 1-3 leaf stage prior to
tillering. Jointed goatgrass can be treated in the fall or spring. Beyond herbicide
can be applied from 4-8 oz/A in combination with nonionic surfactant (NIS) and
urea ammonium nitrate (UAN).
Implementation of Best Management Practices for Management of Jointed Goatgrass
The National Jointed Goatgrass Research Program has funded several large scale,
on farm trials in the Great Plains for economic analysis and demonstration
of current practices compared to new integrated approaches. Two large-scale
projects are located in Otis and Haxtun, CO. The studies were initiated in
the fall of 2000 and will continue until 2007. The study objectives are to
examine the use of CLEARFIELD* technology in combination with corn, millet
and sunflower rotational crops in effort to manage jointed goatgrass populations.
Wheat yields in 2003 were 39 and 32 bushels/A at Otis and Haxtun, CO, respectively
for Beyond herbicide treated CLEARFIELD* wheat. Conventionally treated CLEARFIELD*
wheat yields were 35 and 32 bushels/A at Otis and Haxtun, CO, respectively.
Corn, millet, and sunflower have yet to be harvested.
Beyond Herbicide - Winter Annual Grass Greenhouse Dose Response Study
Greenhouse studies were conducted from 2000-2003 to examine
winter annual grass response to Beyond herbicide applied at 10 application
rates and 3 growth
stages. Herbicide application rates ranged from 0.0005 – 0.256 lb ai/A.
Winter annual grass growth stages were 2-3 leaves, 1-2 tillers and 3-5 tillers.
Study results show that jointed goatgrass is more susceptible to Beyond herbicide,
followed by downy brome and feral rye. The results observed in the greenhouse
studies confirm results observed in field trials. These greenhouse studies
provide information that can be used to make more precise label recommendations.
In vivo ALS Assay
It is not known how rapidly ALS (acetolactate synthase) activity recovers
in CLEARFIELD* winter wheat after application of imazamox. In addition, the
development
of resistance in winter annual grasses is also a concern. We want to determine
if an in vivo ALS assay could be used to measure the recovery of ALS in CLEARFIELD*
wheat as well as to monitor ALS activity in the winter annual grasses. Studies
were conducted to measure ALS activity in CLEARFIELD* wheat, susceptible
wheat and in winter annual grasses using an in vivo bioassay. Dr. Dale Shaner
designed
an assay using plant leaf disc to measure ALS activity. Leaf discs are placed
in vials containing a solution that aids in the release of the ALS enzyme.
The process takes approximately 24 hours to gather the results. Although
the assay is still in the developmental stage, early results indicate the
assay
can detect resistant and susceptible plants in the field. With assistance
from Colorado State University, farmers might be able to use the assay to
determine
if resistant weeds have developed from the use of ALS herbicides.
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