I have an ornamental cherry (I think it is called a Maytree or May Cherry) that was planted about 6 years ago. It seems quite robust every Spring and has grown to nearly 18-feet in height. The problem is that many leaves are turning now, becoming red and dropping off in early July. For the past two years, a large colony of aphids attacks it in April. I respond with lady bugs and am assisted by a fleet of Wilson's warbler; who pick the tree quite thoroughly for a week, before migrating off. I also note that, on occasion, sap oozes from the trunk near to where it meets the soil. The soil is clay, but the original planting went deep, so that (I think) the drainage is okay -- reaching to a layer of sand underneath near lake level. Should I be doing something for the tree? Is this merely an aphid problem that the tree will eventually conquer or is something more nefarious involved?