I have three weeping willow trees. Two are younger (smaller) and one is larger. The large tree seems to be dropping leaves. Quite a lot of leaves. The two smaller trees lose leave also but not to the same extent. The trees never seem to be bare but it drops leaves nearly consistantly. I don't know why. They all lose leaves in the fall following the first hard frost. Yes it frosts here too. I live in the high desert of California. The wind blows here almost constantly, sometime they are high winds. I did notice that the leaves started to fall off reguarly when the temperature reached the mid to upper 90s for a few days. Unfortunately that is normal here too. I water (not flood) the lawn everyday for 10-15 minutes each time 4 times a day. This has been the case since I bought the house. The trees were put in in 1989ish. The trees seem health and I had them pruned last year. They filled in nicely and are full. I don't have any dead limbs. I did before pruning but now all limbs are covered with leaves. Why are the leaves dropping? I asked one local tree trimmer/arborist and he had no reason. I am cleaning up constantly and this is getting frustrating.