California: Herbicide Resistance Found in Annual Bluegrass

Annual bluegrass is a common winter growing grass in agricultural and urban environments. It is a well-known weed of turfgrass systems but its ability to grow in a range of environments makes it an increasing problem for other agricultural systems.

Annual bluegrass has a short life cycle which may range from annual to perennial, seeds can germinate rapidly and multiple times in a growing season and has a high degree of survival when defoliated or trampled.

Herbicide Resistance Info

All of these traits make chemical control an attractive and primary mode of management for annual bluegrass. This is true for turfgrass systems where managers use regular applications of PRE and POST herbicides and orchard systems where glyphosate is used. To date annual bluegrass biotypes have been reported with resistance to nine mode of action groups.

Recently a population of annual bluegrass in California was identified showing resistance to glyphosate treatment in an orchard cropping system. Glyphosate resistance can be a result of a range of mechanisms that have evolved in a particular plant.

These include, among others, the reduced movement of glyphosate to the growing regions of the plant, the inability of glyphosate to bind to its target in the plant and the metabolism of glyphosate before it can reach its target in the plant cell.

The Weed Science Group at UC Davis is now investigating the extent of resistance in this biotype including possible resistance to other herbicide mode of action groups commonly used in specialty cropping systems.

The possible mechanism of resistance is being researched with an aim to mitigate the spread or evolution of resistance in this common weed in the future.

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