ONIMIL, a forecaster for primary infection of downy mildew of onion 1

Abstract

Onion downy mildew, caused by Peronospora destructor, can be controlled effectively only when sprays are begun in the infection period following first sporulation. Systems analysis was applied to the onion/P. destructor pathosystem in order to understand better the relationships between the factors influencing the establishment of primary infection. A preliminary model able to forecast primary infection, ONIMIL (ONIon downy MILdew), was developed. This model was able to determine, for each day, the probability of P. destructor establishing an infection on onion and its infectivity level, compared with the maximum. The model uses empirical rules and mathematical functions based on meteorological factors.