Fruit tree diseases : Apple powdery mildew

The apple powdery mildew is cause by the fungus  Podosphaera leucotricha, and it can be a real problem if not controlled.

It attacks buds, leaves, blossoms and fruits of apple trees.

Powdery mildew overwinters as a mycelium in infected buds (or twigs) and when spring comes, as buds break dormancy, the fungus resumes it’s growing and spreading spores on blossoms and leaves with the help of wind.

High temperatures ( 20-24 °C ) and high humidity ( above 80% ) are favorable conditions for powdery mildew to appear.

What is interesting about this fungus is that rain actually reduces spore germination and development of the disease.

How to spot it

Small white , flour like, spots develop on the underside of leaves and the leaves become curled.

Sprouts get a brown color and they curl at the top ( like a hook).

Fruits are attacked only if the infection is powerful or the cultivar is sensible to the fungus infection. If attacked, fruits stop growing and drop.

How to control it

• plant cultivars that are resistant to powdery mildew.

• remove infected terminal shoots during winter pruning.

• remove and destroy infected shoots as they appear early in the year.

• spraying with fungicides ( sulfur based ) help stop the infection.