Herbicide resistance is the decrease in susceptibility of a weed population to a herbicide as a result of repeated exposure to the herbicide. The unwise use of herbicides can set the stage for the serious problem of herbicide resistant weeds. Weed characteristics that increase the likelihood of evoking herbicide resistance include wide genetic diversity in the germplasm and short seed life in the soil. Waterhemp which has these characteristics has been found to be resistant to the ALS inhibiting herbicides.
The management strategy to deal with herbicide resistant weeds is to reduce the selection pressure for the evolution of the resistance. The easiest and best method for accomplishing this is through the use of crop and herbicide rotations. Herbicides used in rotation should differ in mode of action. Other methods include using short residual herbicides, tank mixes or sequential treatments of herbicides with different modes of action, increased tillage used in combination with herbicides, and preventing weed escapes from going to seed.
The following information is based on work from the University of Arkansas.
The following examples of weed resistance to herbicides have been documented:
- barnyardgrass resistance to propanil in rice,
- cucklebur resistance to Scepter in soybeans,
- goosegrass and Palmer pigweed resistance to DNA (Prowl, Trflan, etc.) herbicides in soybeans and cotton,
- cocklebur resistance to MSMA/DSMA in cotton and
- johnsongrass to Fusilade and Assure in cotton and soybeans.
Actions that Promote Resistance
Over dependence on herbicides.
- Relying on single herbicide or mode of action.
- Sequential applications of same herbicide or mode of action.
In order to manage herbicide resistant weeds and to prevent the widespread development to resistance, the following strategies are recommended.
General Resistance Management Strategies
- Rotate crops where possible.
- Use preplant tillage, cultivation and other cultural practices for weed control where possible.
- Rotate herbicides having different modes of action.
- Use tank mixtures of herbicides having different modes of action.
- Avoid sequential applications of the same herbicide or herbicides having the same mode of action.
- Control weeds on fallow or set-aside land.
- If you suspect resistance after a herbicide application attempt to eradicate escapes with alternative herbicides or cultural methods, i.e. DO NOT LET THEM GO TO SEED.
