The Q&A Archives: Crabapple Tree Disease

Question: We have a tree in our yard which we think is a crab apple although in 4 years we have had no fruit. This year the leaves have bright red spots on topside. Underside of leaf where spot is has fingerlike projections.
The only other thing I can tell you is that we have had a caterpillar problem. We are in the White Mountain area of NH

Thank you for any help.

Answer: Crabapples are susceptible to a fungal disease called scab. This disease causes spots on leaves, and can affect the fruit, making it deformed and spotty. Once scab attacks a tree it's difficult to control. The best thing for you to do is to rake up and distroy the fallen leaves and remove the fruit at the end of the season. Then in January or February, spray your crabapple tree with a fungicide (such as lime-sulfur) to prevent the disease from reappearing next year. Lime-sulfur is also marketed as dormant fruit tree spray or Bordeaux. It's used on apple trees as a precautionary measure because apples are quite susceptible to scab, too. Best wishes with your crabapple!

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