A general name given to a variety of fungus diseases, usually characterised by a white, mealy growth onand . These are known as powdery mildews and infect many plants, notably aster (Michaelmas daisy), delphinium, rose, apple, gooseberry, peach and strawberry. Peas and vines are also attacked. The powdery mildews are chiefly superficial (to use the scientific term), I.e. they do not penetrate the inner tissues. Downy mildews are deep-seated and reach the inner tissues. They are more damaging in the long run. They occur on cauliflowers, onions, spinach, stocks, wallflowers etc., also roses under glass, and may generally be detected by yellowish patches on the foliage. Both types of cripple growth and lead to defoliation, thereby reducing the crop whether , fruits or vegetables, but plants are seldom, if ever, killed outright. Mildews are encouraged by dryness at the , excessive , sudden temperature changes and bad air circulation.
Prompt removal and burning of infected growths is desirable and spraying with a sulphur or Karathane fungicide will control the powdery mildews. Bordeaux mixture is used to tackle downy mildews. In all cases the principal aim should be to prevent infection of healthy foliage which is so far uninjured. In thecareful attention to and ventilation will do much to minimise attacks.