Weeds make it difficult for plants to survive, since these plants compete with the desired plants for nutrients, space and water. One way to stop these weeds is to use special fertilizers that kill the harmful weeds but do not hurt the crops. Herbicides are also used in order to kill plants that are difficult to get rid of, such as the poplar tree. Unfortunately, some plants that are exposed to too many herbicides develop a resistance to these herbicides.
Plants gradually develop the ability to survive herbicides and reproduce after being exposed to some herbicides that once killed them or prevented them from reproducing. This resistance to herbicides forces gardeners and farmers to use different methods of eliminating these weeds, such as the use of different herbicides and other control methods like mulch.
Some plants become intentionally resistant to herbicides, such as crops that are genetically engineered to resist herbicides. Other plants develop a natural resistance through the process of natural selection, where the plant finds ways to block or breakdown the chemicals found in the herbicides. Also, sometimes the enzymes used by the plant become altered so that they do not bind with the chemicals found in the herbicides. Random mutations are responsible for these changes in the plants. The plants that develop resistances to herbicides outcompete other plants, causing the resistant plants to become dominant.
Some plants are resistant to herbicides before they are even exposed to the herbicide. These plants are sometimes a minor part of the ecosystem until the herbicides start to be applied to the area. Non-resistant plants die off and the more resistant plants come to dominate.
Even though a plant might develop resistance to a particular herbicide, other herbicides will still likely kill the plant. Plants don’t develop a resistance to more than one herbicide very often, though this has occurred in a few instances, such as with the Australian rigid ryegrass, which is resistant to six different herbicides.
Fortunately, plants do not develop resistance to herbicides as quickly and as frequently as insects do because of the slower reproduction rate of plants and the lack of selection pressure placed on plants by herbicides. Still, herbicide resistance is accelerating.
Some herbicide resistance is deliberately initiated by agricultural scientists through genetic engineering. Some herbicides cannot be used because the beneficial plants and crops nearby the weeds are also susceptible to the herbicide. However, through genetic engineering, geneticists are able to develop crops that have resistances to the herbicides most effective at killing the nearby weeds.