Downy mildew (latin name – Peronospora destructor) develops on leek (Allium porrum) when humidity is high and night temperatures are low. These conditions are usually seen in the autumn.
Downy mildew is characterized by pale–green, yellowish to brownish areas of irregular size and shape (oval to cylindrical) on infected leek leaves. Masses of spores are produced on the surface of the leaves, which turn from transparent to greyish, and then rapidly become a violet colour. Leaves become girdled in the region where mildew develops and the leaves collapse, resulting in dead leaf tips. The dead leaf tissue is often colonized by purple blotch, which is dark in color and obscures the downy mildew.
Downy mildew seldom kills leeks, but the leek growth may be reduced.
The relatively cool, moist weather that the UK has been experiencing favours the development of downy mildew in leeks.
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Downy mildew of peas (Latin name – Pisum sativum) is caused by Peronospora
viciae, which also infects broad beans. Downy mildew is regarded as the
most common foliar disease of peas and is a major problem in the UK,
particularly in the east. Late-drilled peas are the worst affected.
Downy Mildew Symptoms in Spring Beans & Peas
Yellowish blotches appear on the leaves, with a pale mauve or brown
mould on the underside. Infected pods are spotted and distorted.
mildew-spores
Downy mildew is more likely to appear when temperatures are below 10°C,
& when crops have been wet for more than 12 hours.
mildew-on-one-leaf
Downy Mildew Control in Spring Beans
* Crop rotation reduces the possibility of downy mildew
* Plants affected with downy mildew should be burnt after picking
the crop
* Sprays are available to control downy mildew. Although the disease
may be present when the crop is in flower, no benefit will accrue
from spraying at this time. Always follow the manufacturer’s
instructions on the spray container.
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