Diseases are a major concern for greenhouse growers and can be a key limitation to profitable plant production. Disease management in greenhouses is critical because the warm, humid environment in these structures provides optimal conditions for reproduction of many pathogens. When disease management is neglected, pathogen populations build-up and continue to increase as long as there is susceptible plant tissue available for infection and disease development. Infected plant tissue, infested soil, and pathogen inoculum (such as spores, bacterial cells, virus particles, nematode eggs) all serve as sources of pathogens that can later infect healthy plants.