Tuesday, August 10, 2010

Plant pathology: Problems with peas

Downy Mildew
 Peronospora viciae
This fungal disease causes the upper surface of the leaf to turn yellow while beneath the leaf a grey brown furry growth develops. This is worse during humid weather. Watering late in the day should be avoided.
Powdery mildew fungus (Erisphe pisi) showing as white powdery coating on leaves while parasitic fungi 'black leg' (Mycosphaerella pinodes) and 'chocolate spot' (Ascochyta pisi) cause brown or black marks or spots on the stems and leaves.
In Australia, the pea variety Greenfeast, a New Zealand selection from Lincoln, has long been regarded as having good disease resistance though it may not be entirely free from an attack by powdery mildew. It is a recessive gene in peas so that even wild peas from which the modern cultivars have been developed are sensitive to it.The theory behind this is that mildew is encouraged by the plant as it attracts beneficial insects such as ladybirds which appear to feed on the fungal colonies, thus protecting the peas from a worse insect invader.
Other resistant varieties include the American bred Knight, Kodiak, Mayfair, Rascal, dwarf Oregon Snow Pea and the sugar snap variety Super Sugar Mel. Not all these varieties are available here.
A degree of control of fungal diseases in peas can be achieved by spraying with potassium bicarbonate or by using a sulfur powder.

No comments:

Post a Comment