Without knowing the kind of tree, it could be anything. But given that this summer has been unusually hot and dry for wide parts of the country, I'd surmise it was just stress and the falling leaves are an additional indication of that.

It happens here with various tree species as well.

Here is the picture. you will see the tree and the problem.

The tree has flowers in the spring and I do not know the type of the tree since I am the new homeowner. It is not very tall, but its not a small tree. It stands in the middle of our front yard. And the tree faces southeast.

Cindy, for the most part, do not be concerned about the appearance of leaves in late summer/fall. By this time of year, it is completely normal for various insects, mites, and fungal and bacterial pathogens to have had their way with the plant. It's OK. For example, that leaf you are showing us; It likely has been chewed or sucked on by insects, the brown blotching could be some type of fungal infection, but again, this is the end of the growing season and it is to be expected that by now (within this one year), some of this stuff will have occurred.

Your photo shows just this: A late-season leaf which has already done its work for the year, having been affected by a range of insects and other entities. Please do not try to spray some material because of this. It would do no good whatsoever.

IF this tree is sufficiently important to you, and you do actually want to try to control this scab ()or whatever it is), you will have to do two things: First, get a positive ID. Here in Wisconsin, we've got something called the Plant Disease Diagnostic Laboratory, that is, the governor and his fellow short-sighted minions haven't completely cut the program off at the knees yet. If your area has something like this, talk to them and see what they need for a sample. There are fairly detailed methods necessary to handle these samples in order for the lab people to get anythin g out of them.

Then, upon making a positive ID, you will be offered a range of control regimens. But I can tell you right now, this is almost never done. Nowadays, the primary focus is in breeding cultivars with resistance to these pathogens. But above all else, it is likely that next spring, the tree will leaf out normally. This is nearly always how it goes.

what tom said.. simplified ... its fall ... trees are shutting down .. its just that time of year ...

if there were any stressors .. then you can have early leaf fall ... including diseases drought.. heat.. etc ....

your leaf looks like my crabapple ... its subject to a bunch of diseases ... i ignore it ...

there are more resistant crabs.. if that is what it is ... personally.. i am not going to be spraying a crab.. like i one would have to spray a fruit tree .. life is too short ... and im too cheap to spend the money ... you would have to start spraying in late winter.. and probably spray it a couple more time during the season ...

never forget ... you can always get rid of a problem plant .. including trees ... to avoid tree hugging. guilt .... just plant 2 to replace it.. ma nature.. plus one ...

ken