BOT 552: PLANT DISEASE MANAGEMENT

III. Polyetic (multi-year) cyclesSome pathogens take several years before inoculumthey produce can be disseminated and initiate newinfections.May not cause many new infections over a given areain a year, amount of inoculum does not increasegreatly within a year.However, because they survive in perennial hosts theyhave almost as much inoculum as they had at the endof the previous year.Inoculum may increase steadily (exponentially) fromyear to year and can cause severe outbreaks whenconsidered over several years.