By decreasing the number of weeds, the farmer increases the amount of crop grown. A good example of such a crop is GM cotton, which is often grown in the United States for cottonseed oil. If a crop can kill pests, the farmer dose not have to spray so often to kill pests. An example of a pest-resistant crop is maize,which is similar to corn. there is a bacterium in the soil which produces a poison that kills insects,but it is harmless to people.