A net-like russeting can cut the value of fruit in half and with some orchards spraying up to 15 times per growing season the economic losses from P. leucotricha are high.

[1] Powdery mildew, caused by the obligate biotrophic ascomycete Podosphaera leucotricha, is one of the major diseases of cultivated apple throughout the world.

Flowers are deformed with pale green or yellow petal and are covered in white mycelium and spores.

[5] In spring, the overwintered fungus is evident as 'primary' mildew on leaves emerged from buds infected during the previous growing season.

[7] Apple shoots have a long growing season causing the tree to stay susceptible for several months.

[4] The pathogen is supposed to spread almost exclusively asexually, although ascospores might be an underrated additional source of infection.

[5] Occasionally the sexual state of P. leucotricha occurs as pin-head sized brown/black fruiting bodies (ascocarps) among mycelium on infected shoots or leaves.

Spraying occurs from green cluster until vegetative growth ceases, and occasionally post-harvest if terminal buds regrow.

June is a critical time for monitoring and mildew control as this is the period for rapid extension growth and also when fruit buds are forming and sealing for next spring.