Crabapple dropping leaves all season

Although our big crabapple leafs out beautifully in spring and blooms abundantly, the canopy loses leaves all season. Already, as usual, there's a steady sift of dead leaves from this tree. It will be almost leafless by Sept. What's the explanation? I have hosta and other perennials beneath it. Could these plants cause the tree's leaf loss? It is 35+ years old.
Thanks for thoughts on this!

cedar apple rust

Or apple scab...

Show us pictures of the tree, closeups of leaves discoloring on the tree, and pics of the leaves on the ground. These foliar diseases are quite common on older non-resistant selections of ornamental Malus - which is why there are so many newer disease-resistant selections.

This condition has nothing whatsoever to do with the perennials you have in your garden.

Since your post, Weerobin, I've read online about CAR, and our conditions clearly fit the profile.There are countless cedars in our area, with many very close to our property. Our crabapple usually bears abundant but very tiny fruit--the size of a grape or even a pea, maybe. I never worried about this, but it could be another symptom of rust. Not one tree specialist of the many who have pruned it at various times over the years has mentioned rust. Still, your diagnosis may well be correct. Weather conditions this year have been optimal for the transmission of spores.
VV: I will find a camera and post some pictures, as you suggest. May take me a couple of days to figure out how to do this.

Did you notice rust-like symptoms on the leaves? They're usually pretty obvious so if you've had tree specialists out when it was exhibiting symptoms I suspect they would have recognized it as rust. Scroll down to the cedar apple rust section on this page and see if the picture of the leaves looks anything like what happened to your tree. http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2000.html

There are pics of some other apple diseases on that page too so if it doesn't match the rust maybe you'll spot something else that looks like a match.

colordiva:

Here is information straight out of your state's cooperative extension service. Scroll down the page for information on diseases that are common to crabapples/apples - like scab, rust, frogeye leaf spot, and powdery mildew. All of these are foliar diseases that afflict non-resistant crabapples, which it sounds like you have.

http://extension.umass.edu/landscape/fact-sheets

Small fruit is not necessarily an indication of a problem. As you read more about this ubiquitous plant, you'll find that the trend among the over a thousand named selections of ornamental crabapple is for disease resistant plants with small persistent fruit - not large edible fruit.

Good luck, and look forward to seeing some pictures. Once you take some and download them onto your computer, it is pretty much a snap to post them here. There is a TEST forum where you can practice, even.

Thanks so very much to all for your responses! The pix online at the extension services, esp. Clemson's, convince me I have a cedar apple rust problem. The marks on the pictured leaves are all too familiar. And, I found ugly little brown knots on our nearby cedar. Still, I am working to get some photos of my tree's leaves into a post here--a capability I need anyway.
I lost two mature trees in recent storm events, and last year, our neighbors suddenly removed every evergreen on our shared lot line because of their new solar installation. Those evergreens were old and huge, and they did have problems, but I really mourn the loss of beauty, shade, and privacy. My crabapple has become so important.
Again, thanks for your thoughtful, quick help.