Apple scab overwinters in infected leaves on the orchard floor. The spores (called ascospores) mature around the same time that the new growth begins to appear in the spring (green tip stage).

Spores are released during rainy periods, and can be carried long distances in air currents. Ascospores land on new leaves, blossoms and fruit, and under the right temperatures - if the leaves or fruit are wet long enough for the spores to germinate, a primary scab infection occurs. 

 It is now time to set your green tip date in the BC-DAS scab model. Use the graphs and temperature logs to monitor scab conditions in your orchard. 

The primary scab season lasts until all the ascospores from last year's leaves have been released. This varies from year to year but typically peaks around blossom and ends by mid to late June.