U.S. farmers employ a range of pest management strategies to control weeds, insects, fungi, viruses, and bacteria. They till their soils, rotate their crops, scout their fields, and carefully consider factors such as plant density and planting dates. They also apply organic and synthetic pesticides.
Herbicides are widely used for weed control. These pesticides can be applied before planting, either to eliminate weeds from a field or to prevent new weeds from germinating. Herbicides can also be applied post weed-emergence. Rather than preventing germination, these applications target weeds that are well established and actively growing.
Insecticides are used to control insect infestations. Some insecticides are incorporated into the soil (to treat grubs, worms, and other soil dwelling pests), while others are applied directly to plant foliage (to treat moths, aphids, and other above-ground pests). Most foliar applications need to be properly timed, otherwise they are not effective. Consequently, many farmers scout their fields to determine if/when insects are present.
Fungicides are used to control pathogenic (disease-causing) organisms. Though these pesticides are often applied during the growing season to increase crop yields, they are also applied to prevent stored produce from spoiling.
Over time, an increasing number of U.S. farmers have chosen to cultivate crops with genetically engineered pest management traits (see Genetically Engineered Crops in the United States, ERR-162, February 2014). Some of these plants produce selective, organic insecticides. Others have been engineered to tolerate non-selective, post-emergent herbicides such as glyphosate or glufosinate.
Subsequent to the development of genetically engineered, herbicide tolerant (HT) crops in 1996, post-emergent herbicide use increased, particularly for soybeans. Though pre-emergent herbicide use initially declined, it has recently been increasing in corn and soybeans, perhaps due to concerns about glyphosate resistance (see The Economics of Glyphosate Resistance Management in Corn and Soybean Production, ERR-184, April 2015).
Subsequent to the development of genetically engineered, insect resistant (Bt) crops, insecticide use has dropped in both corn and cotton production (see Pesticide Use in U.S. Agriculture: 21 Selected Crops, 1960-2008, EIB-124, May 2014). However, recent concerns about rootworm resistance to Bt corn seeds may be driving soil insecticide use upwards.
ERS is actively engaged in research to understand how weed/insect resistance develops, how farmers respond to resistance, and the extent to which resistance management practices are effective.