I think it's Japanese Beetles that defoliate mine Helen. It's definitely not from drought because the leaves are chewed and lacey. They bloom early before the Japanese Beetles emerge so it doesn't hurt the flowers any.
I got some free from our city utilities company several years ago and then bought one later at Home Depot(I think) because I thought it would help with cross pollination. The ones I got free bloom at a different time (later) than the one I bought. The cherries that they make don't taste too bad but I only get a couple per shrub every year. The purchased one blooms heavier and is more fragrant. I believe they're grown for retail from both seed and cuttings so some may be better than others. If you decide to get one, get it while it's in bloom so you can pick out the most fragrant one. That's what I did. Walmart, Lowe's, Home Depot, etc. will all have them so they're not terribly expensive.

I like to have a variety of plants. If I had a small yard and was picking something for a special place in my front yard, it wouldn't be the best choice but otherwise it's fine. I think it smells wonderful when it's in bloom and I like the purple leaves in the summer. I don't try to spray it or anything. It doesn't hurt them to be defoliated like that. They bounce back quickly. This is the one that blooms heavier that I bought. It think the flowers start before it has many leaves so that makes it showier too.

Thanks for the good information.