Herbicide resistance: prevention and management

Herbicide resistance is the inheritable ability of some biotypes within a population to survive and reproduce following exposure to a dose of herbicide that would under normal conditions of use effectively control that weed species.   Tolerance is the naturally occurring inheritable ability of all populations of a weed species or crop to survive and reproduce following an herbicide treatment.

How does herbicide resistance develop?

1.    Resistance arises from the selection (survival) of a mutation or small pre-existing population of resistant plants. The rate of development of herbicide resistance in a weed population is influenced by the characteristics of the weed species and the herbicide.

2.    Herbicide resistance is likely to develop if there are high frequencies of resistant individuals in the weed population, and resistance will spread more quickly than in a population where the frequency of resistant individuals is low.  The speed of build-up in resistant population will depend on selection pressure which in turn depends on the dose of the herbicide used, its efficacy and the frequency of use.  The higher the selection pressure the more likely it is that resistance will evolve. 

3.     Repeated use of herbicide with the same mode of action increases selection pressure, while use of herbicide mixtures and/ or integrated measures will reduce selection pressure.  Reducing the dose of herbicides application and repeated use of a single product may encourage the development of resistance.

Prevention and management of herbicide resistance

The management practices must be primarily focused on reducing the selection pressure.

1.  Rotation of herbicides with different modes of action
2.  Use of herbicide mixtures
3.  Use of herbicide when only necessary and at the recommended rates
4.  Control of weed escapes and sanitation of equipment to prevent spread of resistant weeds from affected areas
6.  Regularly scout for resistant/ surviving weeds in herbicide treated fields.
7.  Adopt integrated weed control practices
8.  Use crop rotations

Definitions

escapes – individual plants that are not controlled by a herbicide application that control the majority of the population.  “Escapes” may go on to reproduce and establish a resistant population.

mode of action -  the way the herbicide affects the plant at tissue or cell level.

scout – inspection or survey of the field and crop

For further information on herbicide resistance and its management see www.hracglobal.com/