Onions

Onion thrips (Thrips tabaci) is the most serious pest of onion crops in New Zealand. Their rasping feeding causes whitening of leaves which reduces yields. However their presence in the necks of harvested bulbs and subsequent feeding damage in storage can lead to rots in storage in export shipments. The adults are small, a black colour and are winged. The larvae which cause the plant damage are thin and a white to yellow colour and are usually found in the necks of onion plants.

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.

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.

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.