Scald, caused by the fungus Rhynchosporium orthosporum, typically occurs April-October, from Manawatu and Hawke's Bay south.
Scald causes irregularly shaped lesions or scald-like blotches on leaves and leaf sheaths. These are brown-grey in colour, often appearing grey with brown edges. Lesions can join to affect most of the leaf. Infected leaves often die from the tip down; heavily infected plants are unpalatable to stock.
Spores produced on dead leaves are splashed, blown or carried to new leaves. The disease then persists in cool, sheltered areas. It is most severe during cool, wet periods in early spring and autumn.
Prevention and management
Sow resistant ryegrass cultivars. All Agriseeds cultivars have good resistance to scald. If the disease is noted in winter conserved feed, timely grazing can reduce losses.
Scald on ryegrass leaves.