Onion Pests and Diseases
Typical symptoms: Leaves yellow and die from the tip down.
Prevention and treatment: See How to Treat Common Plant Diseases
Onion fly (Delia antiqua)
Typical symptoms: Leaves wilt; small white maggots are found in roots and bulbs. Young plants may die; infected bulbs rot.
Prevention and treatment: Where onion fly is a recurring problem, protect plants with a lightweight cover. Crop rotation, winter-digging infected land and removing infested plants as soon as the onion fly is noticed can help to limit its effects.
Leek rust (Puccinia allii)
This affects leeks, chives and occasionally other related crops.
Typical symptoms: Distinctive bright orange pustules develop on leaves in summer and early autumn. A severe infection may kill young plants.
Prevention and treatment: This disease is more likely to occur wherepotash supplies are inadequate, poor is a problem, and where nitrogen is applied excessively. Immediate action is not necessary as the disease often disappears of its own accord in the autumn. If leek rust is a recurrent problem, break the cycle of infection with uninfected plants.
Neck rot, (Botrytis aclada)
Neck rot affects onions only.
Typical symptoms: Onions in store develop athat starts in the neck. Grey mould may be present.
Prevention and treatment: Use a minimum three-year. To avoid infection, clear up all crop debris and avoid damage to plants while weeding. Never bend green onion tops over; leave them to die down naturally. Dry bulbs well before storing. Never save seed from an infected plant.
Stem eelworm (Ditylenchus dipsaci)
This pest also attacks a wide range of fruit, ornamental plants, weeds and other vegetables such as French and runner beans.
Typical symptoms: Leaves swollen and distorted; the base of the plant swells prematurely. Plants grow poorly and may die.
Prevention and treatment: Avoid bringing infected plants into the garden. Where the pest attacks, remove infected plants (do not compost) and do not grow another susceptible plant on the site for two to three years.and lettuce are not susceptible.
White rot (Sderotium cepivorum)
This disease affects onions, garlic and leeks.
Typical symptoms: Leaves die back; root growth is poor. A fluffydevelops on the base of onion bulbs and the neck of garlic.
Prevention and treatment: White rot can survive in the soil for 20 years or more in the absence of a host crop so it makes sense to avoid bringing infected plants or soil into the garden. Where the disease occurs, dig out infected plants with a good spadeful of soil and dispose of it in the dustbin. There is no cure for this disease, but leeks may produce a crop on infected land where onions and garlic fail.