How resistance occurs

Herbicide resistance occurs through imposing selection pressure on a weed population. The selection pressure is the application of herbicides, which select for survival of members of the population that contain a mechanism imparting resistance to them. These individuals will survive and reproduce, so year upon year - as long as the same herbicides are used - the percentage of such individuals in a population will increase (Figure 12.5). In practice, population size plays a very important part in the occurrence of herbicide resistance. If selection pressure is exerted, but a population is kept small by other weed management methods, then the number of resistant individuals in the population may increase but the population size will remain small, resulting in less of a problem. Conversely, where population size remains large the number of surviving resistant individuals will be large, and so greater problems are encountered. Therefore, resistance problems in practice are a result of repeated imposition of selection pressure coupled with agricultural practices that result in large weed populations. Factors affecting the speed at which resistance develops include:

• Initial frequency of resistant individuals in the population.

• Size of seed population in the seed bank and the length of time the seeds remain viable.

• The susceptibility of susceptible individuals.

• Repeated use of a single herbicide active ingredient or single mode of action, year upon year.

• Use of herbicides with long periods of residual activity in the soil.

• Use of herbicides with highly specific single modes of action.

Figure 12.5 How resistance occurs. (a) Herbicide application imposing a selection pressure on a mixed population. Light grey = herbicide sensitive; dark grey = herbicide resistant. (b) Repeated use of the same herbicide will repeat the selection process. Susceptible individuals may enter the population from the soil seed bank, from seed from outside the field and from susceptible plants surviving due to poor herbicide efficacy.

Figure 12.5 How resistance occurs. (a) Herbicide application imposing a selection pressure on a mixed population. Light grey = herbicide sensitive; dark grey = herbicide resistant. (b) Repeated use of the same herbicide will repeat the selection process. Susceptible individuals may enter the population from the soil seed bank, from seed from outside the field and from susceptible plants surviving due to poor herbicide efficacy.

Was this article helpful?

0 0
Detoxify the Body

Detoxify the Body

Need to Detoxify? Discover The Secrets to Detox Your Body The Quick & Easy Way at Home! Too much partying got you feeling bad about yourself? Or perhaps you want to lose weight and have tried everything under the sun?

Get My Free Ebook


Post a comment