Onion Spray Programme - Diseases

White rot (Sclerotium cepivorum) is a devastating disease of onions in New Zealand, resulting in significant yield losses during epidemic seasons. It infects the roots and basal plates of bulbs causing a characteristic white mycelium and then a blackening rot of the base of the bulb. Early infections usually kill the whole plant but later infected bulbs spread rots in storage.

Downy Mildew (Peronospora destructor) is destructive of onions in New Zealand reducing crop yields, bulb quality and storage life. First symptoms are yellow oval patches on leaves that turn brown and develop a downy grey sporulation. Favoured by moist and mild weather, Downy Mildew can quickly spread as increasing patches in onion crops.

Often called grey mould, Botrytis cinerea in wet seasons is responsible for the greatest crop losses in vineyards. Classically appears as bunch infections of browning berries with grey sporulation. Late season berry slip skin is also caused by botrytis. Botrytis can also be an issue in other crops including citrus, kiwifruit, onions strawberries and berryfruits.