Onderzoekingen over het optreden en de bestrijding van valse meeldauw (Peronospora destructor) bij uien

The life cycle of Peronospora destructor (Berk.) Casp. was spore - infection - overwintering - new spore. Wind-borne spores infected leaves and seed stalks of the onion. After replanting bulbs of an infected crop in the following year, mycelium may sometimes spread into the developing leaves and cause systemic symptoms. If the weather were favourable, spores would infect leaves of the surrounding crops. The rate of development of the disease was dependent on weather, source of infection, variety and leaf density.
In laboratory experiments relative humidity was most important for the progress of the infection cycle. In field experiments characteristics of weather favourable for infection were derived from 4 circular experimental fields. Data on overall climate collected 2.2 metres above ground gave an adequate forecast of days critical for infection by downy mildew.

Infection could be reduced by cultivation, hygiene and chemical control. The best results were obtained with low-volume spraying of zineb, once every 7-10 days, at the rate of 3 kg in 150-200 litres water per ha.