Powdery mildew

Cause

The fungus Podosphaera aphanis

Symptoms

The fungus can attack petioles, leaves, flower, calyxes, fruit stalks and fruit.

Leaves:

  • White patches of fungal growth develop on the lower surface of the leaf. Under favourable conditions, the patches enlarge and merge to cover the entire lower surface.
  • Leaf edges curl upwards, exposing the white, powdery fungal growth (Fig. 1).
  • Purple to reddish blotches may also develop on leaves.
  • Tiny, round, black fungal structures (cleistothecia) may also be present on the underside of the leaves.

Fruit:

  • Pathogen colonises the fruit and produces white mycelial growth on the seeds giving it a powdery appearance (Fig. 2).
  • Surfaces of the fruit harden and may crack.

How does in spread?

The white mildew contains large numbers of spores, which may be carried long distances by the wind. Dry weather, high-humidity conditions, and temperatures between 15o C and 27o C favour disease development.

The disease may also be introduced through:

  • alternative hosts growing close to strawberry cultivated fields
  • symptomless runners.

The fungus survives on diseased ratoon crops via overwintering fruiting bodies (cleistothecia).

Crops affected

There are several genera of fungi that causes powdery mildew diseases, e.g. Erysiphe, Leveillula, Oidium, Podosphaera, Sphaerotheca and Uncinula. These affect several horticultural crops, trees and woody ornamentals.

Management  options
  • Plant certified runners.
  • Monitor powdery mildew incidence regularly.
  • Remove infected fruit to minimise spread of spores.
  • Use a recommended fungicide program.

Chemical registrations and permits
Check the Australian Pesticides nd Veterinary Medicines Authority chemical database and permit database for chemicals registered or approved under permit to treat this disease on the target crop in your state or location. Always read the label and observe withholding periods.