Downy mildew
Original title: Míldio
Downy mildew, a fungal disease of vines caused by Plasmopara viticola, which began to damage Madeiran vineyards noticeably in 1912; Bordeaux mixture proved an effective preventive treatment.
This disease, which attacks mainly the leaves and bunches of vines, began to cause appreciable damage in Madeiran vineyards only in 1912. The white, powdery patches that characterise it are caused by a fungus of the family Peronosporaceae – Plasmopara viticola – whose branches emerge through the stomata of the leaf and form conidia at the tips of their last ramifications. The mycelium of the fungus lives inside the green organs of the vine, and it is this that directly harms the plant. Downy mildew spreads not only by means of spores (conidia) but also by means of eggs or oospores, which result from the fusion of two dissimilar cells. Bordeaux mixture has given good results in the preventive treatment of downy mildew.