A Guide to Grapevine Abnormalities in South Africa - P.G. GOUSSARD

Downy mildew.

PHOTO 34. Under favourable conditions characteristic white, downy fungal growth (representing millions of spore-producing organs of the fungus and spores) quickly develops on the undersides of leaves.

PHOTO 35. In time the yellow spots turn brown/reddish brown, which is accompanied by the disappearance of the white downiness on the undersides of leaves.

A Guide to Grapevine Abnormalities in South Africa • 31