Answer: Without seeing the problem I can't be certain, but there is a disease called cedar-apple rust. If you have junipers or cedars in your neighborhood, it's possible your tree has the disease. The best approach at this point is to collect some of the affected leaves and place them in a plastic bag. Then take them to your local nursery or cooperative extension office for positive identification of the problem. If it turns out to be cedar-apple rust, both your tree and the junipers or cedars need to be treated with a preventative spray.
Best wishes with your crabapple tree!
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