Downy Mildew of Onions

Peronospora destructor


A fungal disease that shows as oval, pale yellow spots on older leaves that increase in size forming large yellowish areas. In humid conditions grey to purplish furry hyphal growth forms on the spots. It can grow into the seeds or bulbs to carry to the following season. Seedlings of infected seed are soon covered by purplish hyphal growth that forms wind borne spores to infect other plants.

Species Affected:

Allium species.

Chives, Garlic, Leeks, Onions and Shallots


Favoured by moist humid conditions.

Spore spread by wind.

Spontaneous recovery from the disease may occur under dry conditions.

Life Cycle:

Origin and History:



Management and Control:

Plant healthy seed or treat seed with hot water.

Destroy residues of previous crop soon after harvest.

Improve drainage and air circulation.

Apply nitrogen to help plants out grow the disease.

Apply fungicides.

Related and Similar Species:




Collated by HerbiGuide. Phone 08 98444064 for more information.