Hello,

Crabapple trees get many diseases including apple scab, cedar apple rust, fire blight and frog-eye leaf spot. Also, spider mites, aphids and scale insects may cause distortion and browning of the leaves. Read more about diseases of crabapples here: https://extension.psu.edu/crabapple-diseases

Read about insects that attack crabapples: https://hgic.clemson.edu/factsheet/apple-crabapple-insects/

Although newer crabapple species are being bred to resist some diseases, older trees continue to be vulnerable. And, as the season progresses, any one of these conditions could cause the leaves to brown and fall.

Because it is always difficult to tell from a picture, your crabapple tree may have apple scab. I am attaching an article from MSU Extension that discusses apple scab.

https://www.canr.msu.edu/news/why_is_my_crabapple_tree_losing_leaves.

It also explains how to manage the disease.

You can learn how to treat and manage your crabapple tree here: https://williamshane.weebly.com/apple.html

As fall approaches be sure to clean up and dispose of diseased leaves from under the tree because the fungal spores from the disease can splash back onto the leaves and reappear in the spring. Also, make certain that the tree is properly watered—one inch of water per week in preparation for the winter months.

You could also consult a certified arborist. Go to www.treesaregood.org, the website of the International Society of Arboriculture to find an arborist in your area.

Thank you for contacting Ask Extension.