Green manures and plant disease management

The use of green manures, which involves the incorporation of fresh plant material, has traditionally been primarily for the purpose of soil enrichment through the addition of plant organic matter and nutrients. However, green manures produce many changes in soil physical, chemical and biological properties, and may also result in suppression of specific plant pathogens and diseases. Green manures increase soil microbial biomass and activity, and cause distinct changes in soil microbial populations that may be partially responsible for suppression of diseases. However, green manures of different crops and cultivars may vary considerably in their activity or efficacy against different pathogens and diseases. In particular, green manures of Brassica and related crops have emerged as most effective for management of multiple plant diseases due to their biofumigation potential, which refers to the suppression of pathogens and disease through the release of volatile toxic breakdown products, as well as other unique effects on soil microbial ecology. Brassica crops and other green manures have been used to control a variety of plant pathogens, including species of Rhizoctonia , Verticillium , Sderotinia , Phythophthora , Pythium , Aphanomyces and Macrophomina , in various crop production systems, such as for the management of multiple soilborne diseases of potato, including black scurf, common scab and Verticillium wilt. Although disease reduction with green manures can be variable and provides only partial control, it is a versatile and readily-implementable additional management strategy that should be used as an important component within a larger integrated disease management program to provide improved sustainable production systems.