The most important hop disease. It spreads through fungus spores. Affected areas on the leaves are lighter in colour and the undersides of the leaves have a grey fungus growth. The flowers become hard and do not develop; the umbels have brown spots.

The peronospore warning service in cultivation areas enables targeted control. It provides daily reports on infection threat, airborne spores, aphids and humidity deficit in the air.

Current information on the peronospore warning service is available here: Peronospore warning service