Management of the environment for the control of pathogens

Abstract

Pathogens can be controlled by management of the environment of (1) the host plant, to maximize resistance, (2) nonpathogens associated with the pathogen, to enhance antagonisms, and (3) the pathogen itself, to limit its activity or longevity directly. Each can be illustrated with controls developed for root diseases of Pacific Northwest wheat. For example: management of plant water potentials to minimize water stress in the host controls Fusarium foot rot; root-colonizing fluorescent pseudomonads, with ability to inhibit Gaeumannomyces graminis by antibiosis, achieve highest populations on roots and provide best control of take-all at rhizosphere matric water potentials of —0.3 to —0.7 bar (1 bar = 10 5 Pa) and rhizosphere pH values below 7.0; and infection of wheat seedlings by Pythium spp., being directly limited by soil matric water potentials drier than —0.4 to —0.5 bar, is controlled by sowing in early autumn while the seed zone is still well-drained or by burning surface residues to expose the soil to drying, and possibly also killing propagules by heat-treatment of the soil. Depending on the host-pathogen-nonpathogen interaction, tillage can maximize host plant resistance, intensify antagonism of pathogens by nonpathogens, and directly limit inoculum potential of the pathogen in soil.