Like all cryptogamic diseases, also known as commonly fungal, powdery mildew (more commonly known as white sore, fog or manna) develops mainly in the presence of humid, moderately hot climatic conditions and in case of poor ventilation.
It is a very common disease in the northern areas, which manifests itself with an inflorescence of the mycelium (fungus), which can be found as a whitish dust with partial discoloration of the leaf. In correspondence with these areas the leaf first turns yellow, then necrotizes (becomes dry); sometimes powdery mildew can occur with small circular perforations of the leaf page. This parasite develops in hot and humid conditions, with temperatures above 6-8 ° C, but below 30 ° C, therefore in spring and autumn.
The badly white it affects many very different plants: oaks, roses, vines, apple trees, peach trees and many others are affected. The damage done may consist in a slowdown in growth or loss of the crop (e.g. in the vine).
A good preventive remedy can be to place the affected plant in a well-ventilated area or to prune well lit and aerate every leaf of the foliage. If this is not possible, we recommend first of all to avoid watering in the evening hours in periods with average temperatures. It is then usually resorted to the repeated use of antioid products such as sulfur, dinocap, benzimidazole, pyrimidine, triazole derivatives; in the case of the use of fungicides, it is recommended to perform 2-3 interventions per year, further interventions with the same active principle could cause phenomena of resistance to the product.
In organic farming, sulfur can be used as a prevention, or a powdery mildew antagonist, ampelomyces quisqualis, can be used, which seems to give excellent results.
Powdery mildew is a pathology difficult to combat, given the resistance of the fungus to both chemical and biological treatments. What we know how powdery mildew or white sore, in fact, is a disease caused by a genus of parasitic fungi that prefer almost all the various types of plants, both horticultural and ornamental. In particular conditions, powdery mildew can also attack greenhouse plants and large-scale crops. In the event of a crop infection, the economic damage can be incalculable. No less important are the aesthetic damages, damages that mainly concern the flowering and ornamental plants.