Question
I have a tree in my garden which I think is a cherry blossom tree.  It flowers with beautiful pink blossom in April - May.  The problem is that its leaves become diseased and get shed by the tree, making the tree look quite bare when it has finished blossoming and making a terrible mess on my lawn. If I remember rightly from last year, the leaves have brown patches on them.  Any suggestions what I can do to prevent this. - Thanks

Answer
Sounds like Cherry -- Leaf Spot.
Cause: Blumeriella jaapii (formerly Coccomyces hiemalis), a fungus. It overwinters on fallen cherry leaves and in spring produces large numbers of spores from the previous year's leaf infections. Air currents and rain move spores. In spring, with moisture, they initiate new infections on young leaves through the stomata. Once unfolded, leaves are susceptible throughout the growing season, but susceptibility decreases with age.

Symptoms: On the sour cherry leaves, variously colored spots develop on the upper surface. The spot or lesion rapidly enlarges, becoming brown or purple, and dies from the center out. Infected spots are irregular or round and are over the entire leaf surface. Individual spots never become large. They merge together to kill large areas of the leaf. Spot development precedes yellowing and leaf dropping. The area adjacent to the spot may remain green while the rest of the leaf turns yellow. Diseased leaf tissue may separate from healthy tissue, drop out, and give the leaf a shothole appearance.
On sweet cherry leaves, spots often are larger and nearly circular. Cream-colored spore masses of the fungus appear on the lower leaf surface associated with the spots on both sweet and sour cherries. On fruit stems, infections sometimes girdle the stem to cause a fruit drop. While infections occur on the fruit, they are less common than on foliage.

Cultural control: Rake up and destroy infected leaves.

Chemical control. Sprays for control of this disease are usually begun in spring, just after bloom, and are continued regularly until one or two weeks after harvest. Fungicides containing dodine, fenarimol, fenbuconazole, pyraclostrobin + boscalid, tebuconazole or triflumizole are effective in control of this disease. Captan and chlorothalonil are registered for use on cherry trees. Check with your local nursery/garden type sore for a fungicide for cherry leaf spot.