Pesticide use has changed considerably over the past five decades. Rapid growth characterized the first 20 years, ending in 1981. The total quantity of pesticides applied to the 21 crops analyzed grew from 196 million pounds of pesticide active ingredients in 1960 to 632 million pounds in 1981. Improvements in the types and modes of action of active ingredients applied along with small annual fluctuations resulted in a slight downward trend in pesticide use to 516 million pounds in 2008. These changes were driven by economic factors that determined crop and input prices and were influenced by pest pressures, environmental and weather conditions, crop acreages, agricultural practices (including adoption of genetically engineered crops), access to land-grant extension personnel and crop consultants, the cost-effectiveness of pesticides and other practices in protecting crop yields and quality, technological innovations in pest management systems/practices, and environmental and health regulations. Emerging pest management policy issues include the development of glyphosate-resistant weed populations associated with the large increase in glyphosate use since the late 1990s, the development of Bt-resistant western corn rootworm in some areas, and the arrival of invasive or exotic pest species,such as soybean aphid and soybean rust, which can influence pesticide use patterns and the development of Integrated Pest Management programs.