Herbicides and insectisides are the most commonly used of the two on annual crops. Herbicides are used to control competitive weeds. Cultivators and other tillage practices fight weeds mechanically, but they promote soil erosion. If soil conservation is desired, the only other real alternative is the use of herbicides. Fungicides are used to kill fungal diseases.
Fungicides are generally expensive to apply.
The use of chemicals for insect control dates back to 1000BC when Homer referred to using sulfer to divert pests. One of the first synethic insecticides was Lethane marketed in 1932. Insectides are easy to apply to fields and cost effective. Their use creates a more affordable and more visually appealing crop. Consumers desire healthy foods, but they buy with their eyes.