White rust of Spinach

This pathogen is more closely related to downy mildew-type pathogens than the true rust pathogens. The source of the white rust pathogen that initiates epidemics is not known, but the pathogen is known to survive in infested crop debris as dormant resting structures (oospores) and, in milder climates, as mycelia and sporangia. Oospores are thought to disseminated by splashing rain and irrigation water, and possibly by blowing soil. In warmer climates, sporangia produced on weeds can be deposited onto spinach by wind, whereupon they germinate and produce a mobile spore called a zoospore. Zoospores penetrate plants through natural openings, eventually germinate, and form mycelia in spinach tissues. Disease is favored by cool to moderate temperatures (50 to 68ºC) and abundant rainfall.
Diseased spinach plants produce windblown sporangia that serve as secondary inoculum, infecting other plants and beginning the disease cycle again. Oospores eventually form in diseased tissue and overwinter in infested crop debris and the soil.