Thomas from Wheaton Il. writes
For the best treatment, you first want to identify the exact issue with your crabapple trees. This article from the Penn State Extension service has several descriptions and photos of common crabapple problems. If you are still having trouble identifying the issue, then we recommend contacting a local Master Gardener or arborist. We can then assist you with selecting any products which may be appropriate for your needs.
Answer last updated on: 06/19/2018