Crab apple tree disease diagnosis - Ask Extension
I was shocked to see that my tree has several areas of leaf yellowing. There are also dead branches and large branches that have a blackish discolora...
Knowledgebase
Crab apple tree disease diagnosis #940911
Asked July 29, 2026, 1:12 PM EDT
I was shocked to see that my tree has several areas of leaf yellowing. There are also dead branches and large branches that have a blackish discoloration. The yellow leaves have geographic spots on them. Is this apple scab? Does the tree have more than one illness?
Oakland County Michigan
Expert Response
Hello,
This does appear to be apple scab, a common fungal disease that affects crabapple. Because fungicide does not cure fungus, but can only prevent it, there is not much you can do at this time of year. Due to the severity of the outbreak, you should consider treatment next spring. The following article discusses this disease and management, including types of fungicide that can be used.
https://extension.umn.edu/plant-diseases/apple-scab#fungicides-to-protect-ornamental-crabapples-from-apple-scab-3652960
This fall, fallen leaves should be bagged and put in trash, rather than left in place or composted. Consider pruning next winter/early spring to increase air movement within the tree canopy.
This does appear to be apple scab, a common fungal disease that affects crabapple. Because fungicide does not cure fungus, but can only prevent it, there is not much you can do at this time of year. Due to the severity of the outbreak, you should consider treatment next spring. The following article discusses this disease and management, including types of fungicide that can be used.
https://extension.umn.edu/plant-diseases/apple-scab#fungicides-to-protect-ornamental-crabapples-from-apple-scab-3652960
This fall, fallen leaves should be bagged and put in trash, rather than left in place or composted. Consider pruning next winter/early spring to increase air movement within the tree canopy.
