Powdery Mildew

Press, Volume CVII, Issue 31564, 29 December 1967, Page 3

Powdery Mildew

Powdery mildew will become obvious now on many apple trees, some varieties such as Lord Wolseley, Cox’s Orange Pippin and Gravenstein being more susceptible than others.

This fungus disease is carried over from season to season on infected spurs, buds and lateral tips where it lies dormant until the buds begin to move in spring. Under suitable temperature and moist humidity, winddistributed spores are liberated to infect neighbouring leaves.

Infected buds give rise to diseased shoots, which may fail to grow and frequently die. A white mealy appearance characterises its presence, which will be noticeable on affected leaves also. These are generally much narrower than usual and curled up at the edges. Premature fall is likely where infection is severe. Flower buds are distorted and infected flowers rarely set fruit. Fruit which does form is usually russetted, showing a yellow-brown tracery over the surface or may even be scabbed or deformed on one side. Over winter infected shoots are readily indentified by

their dry and withered appearance. Control should commence in the dormant season with the pruning back of all diseased twigs to healthy wood. These prunings should be gathered up and burnt. The use of lime and colloidal sulphur from tight to open cluster and thereafter the application of the specific fungicide karathane will help to control the disease further.