Apple scab in Calgary

Apple scab or Venturia inaequalis is a common fungus disease in Calgary, which affects trees in the Malus (apple) family. The disease causes yellow spots on fruits and twigs that turn black over time. Reinfestation takes place through wind and rain dispersal in the late spring after reproduction in the leaf litter over the winter.

Trees affected by Apple scab

Which of my trees should be inspected for Apple scab?

Apple Scab can affect all varieties in the Apple family – some are more prone to the disease than other varieties. Recently efforts are being made by fruit producers to create varieties that are more resistant to the disease.

  • Apple trees
  • Crab apple trees
  • Pear trees

Is my tree infected with Apple scab?

Common symptoms linked to Apple scab are

  • Development of yellow/black spots on leaves, twigs and fruits.
  • Diminishing fruit and flower production.
  • General unhealthy look.

Following pictures can help you determine if your tree is infected with Apple scab.

Apple scab Calgary overall

Apple tree infested with Apple scab. William Jacobi, Colorado State University,

Apple scab Calgary infected leaf leaf

Leaf infected with Apple scab. James Chatfield, Ohio State University,

Apple scab Calgary

Apple infected with Apple scab. Bruce Watt, University of Maine,

Apple scab spores

Apple scab spores. Jody Fetzer, Maryland National Capital Park and Planning Commission,


Can Apple scab be treated?

There are several measures that can be taken to control the affects of Apple scab.

Mechanical measures

  • Removal of infested leaf litter around the trees.
  • Pruning of the infested twigs.

Chemical control

Apple scab can be controlled by a wide variety of organic and non-organic chemicals. Applications should be done early in the year for optimum effect and minimal impact on birdlife and the environment.

Yes my tree is infected!

Call your certified arborist for a professional diagnosis and a proper treatment plan.