I have a Purple Prince Crab apple tree approx. 15 years old. This season especially, the leaves have been hit with a brown marking and are falling off very fast. The best I could find on the net was “apple scrab” but no treatment or cre. Please help before I lose my tree.
Thank you for contacting the Toronto Master Gardeners with your inquiry.
Apple Scab is very common after a wet spring, like we have just experienced. It begins with olive green spots that turn black, and mid-summer leaves turn yellow and drop off. The fungus overwinters in infected leaves, dead bark or fruit on the ground. The spores from the fungus then start developing in late winter or early spring, and are released into the air by rain, wind or insects. It then germinates on the new leaves when their surface is wet/humid and begins creating the spots. Heavy infections cause the leaves to turn yellow and drop off at this time of year.
For more information related to apple scab, please review the following website:
https://www.omafra.gov.on.ca/english/crops/hort/news/orchnews/2013/on-0413a7.htm
One of our earlier posts entitled Crabapple Tree – Help! has useful information on how to treat and manage this fungal disease.