What factors influence the rate of evolution of resistant weeds?
The first factor is the rate at which a gene for resistance spontaneously appears in the population. Weeds have a short life cycle and produce many offspring. Both traits predispose them to a higher probability of resistance genes appearing in the population when compared to species with long life spans and few offspring. Another important factor influencing the rate of resistance evolution is the level of selection pressure imposed by the herbicide. If an herbicide is used repeatedly and is the sole weed control strategy, resistance will evolve much more rapidly than if the grower uses a variety of different tactics, such as cultivations and crop rotation, and varies the classes of herbicides the weed population encounters.
