Hello,

Right now, rake up leaves fruit and twigs, bag and discard, to reduce the fungal spores in the area.

Follow the tips in this article, which shows correct pruning controls as well, and that describes when and what to use for control in the spring. Note that timing based on the bud stage  is important.

https://extension.umn.edu/plant-diseases/apple-scab#fungicides-1165363

This chart shows bud stages for crabapples and apples:

https://s3.wp.wsu.edu/uploads/sites/2086/2014/05/budctap.jpg

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