People have long endeavored to protect field crops from disease, pests and weeds. These methods include breeding varieties resistant to pests and diseases, cultural control of diseases and pests by plowing and removing crop debris after harvest, weed control using vinyl sheeting and spreading straw, physical pest control such as soil disinfection using solar heating, and biotic control using natural enemies such as spiders. In addition, agricultural chemicals are used because they produce certain effects with less effort.