WSU Tree Fruit Research & Extension Center

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Tuesday, January 23, 2018

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4331. McGill, Steve. 1990. Handling herbicide resistance in Russian thistle.. The Furrow (April 1990, NW edition).
Herbicide resistant biotypes of Russian thistle have been identified for Glean and Finesse. These herbicides can no longer be used alone for this weed. More tillage may have to be substituted in some situations, and implements which leave maximum surface residue are recommended. A heavy infestation of Russian thistle reduced yields of spring wheat 11% in a wet year and 55% in a dry year, so control is important for moisture conservation.

10118. Washington Assoc. of Wheat Growers. 1991. Glean withdrawal.. Growers Guide, Apr. 1991, p. C10.
Cereal growers in seven Great Plains states will no longer be able to use Glean herbicide from DuPont because of the spread of weed biotypes resistant to the herbicide. When Glean is used repeatedly, especially in monoculture cereal production, the selection pressure on resistant biotypes can increase. The product will still be available in the Pacific Northwest where the environmental conditions are favorable for faster product breakdown so the selection pressure for herbicide resistant biotypes is decreased. Recommended resistance management guidelines are rotating crops, changing herbicide programs, using shorter-residual herbicides and not letting weed escapes go to seed.

10634. Anon.. 1991. Herbicide resistant weed problems.. Growers Guide, July 1991, p. B11.
During the last 30 years, 46 species of resistant weeds have been confirmed, with sulfonylurea resistance being the most recent. The problem could escalate during the next 5-10 years, according to an American Chemical Society report. More attention needs to be given to prevention of herbicide resistance.

11262. Maxwell, B.D.. 1992. Weed thresholds: the space component and considerations for herbicide resistance.. Weed Technology 6:205-212.
As an extension of weed threshold models in which crop losses are based on weed density, an alternative model for grass weeds in cereal crops is proposed that incorporates the theoretical importance of selection for herbicide resistance, initial weed population frequency, and weed seed dispersal. Simulations suggest optimum weed population levels (thresholds) for maintaining genotypes that are susceptible to control practices and which minimize crop yield reductions. Weed population frequency, in combination with dispersal and competitive traits may determine optimum weed management strategies. Model simulations indicate that understanding how agricultural practices select for "weedy" traits (e.g. herbicide resistance, competitive ability, dispersal potential) may be important in determining weed density thresholds.

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