Why are the Leaves on my Tree Falling?

I have a corkscrew willow tree that is losing all of its leaves. It does not appear to have any bore holes and it's not seeping any where that I can see. It is getting plenty of water. I water twice a week for an hour each time. We have been in our home for 5 years and it has never done this in the past. It is shedding leaves just like it were fall. The tree is at least 25 years old and quite large. We really enjoy having it. What can I do? Thank you, Aaron Wilcox Response by commercial applicator Hey guys, just thought I would let you know that I have seen several willow trees with spider mites and the leaves are dropping. A caller mentioned that a minuet ago. "JimMacduff"diamondtree@earthlink.com The problem could be spider mites as described in our section on mites. Unfortunately there are many other suspected problems when large trees lose their leaves. One of the most common is summer leaf scorch. Temperature stress in plants takes many forms. The direct stress from heat are drying out and scorching from burning and lack of water. From cold the direct damage is freezing tissue that destroys the fruit, leavs and other plant structures. Some of the damage that we now see on plants is attrubutable to the weather last fall. The weeek before Thanksgiving it was 80 degrees. Thanksgiving Day we had a severe snowstorm that had temperature well below freezing.That damage to trees is more pronounced when the hot temperatures arrive and the damage water conducting tissue of the plan will not allow the water to move. Indirect causes include increased damage form certain diseases and proliferation of insects, reduced flower and fruit formation. Even soil problems of alkalinity, salts and soil drainage are affected by the heat. Many so call experts claim the heat has no affect on the growth of warm season plants. In biological systems most plants grow best at temperatures of degrees. Once temperatures get above degrees, the growth starts to slow down. Add another degrees and the growth slows to almost nothing. When plants cannot move enough water from the soil to the leaves the leaves scorch or wilt. If it continues to happen the plant will lose its leaves and can eventually die. Scorch in and of itself is not the disease but is the symptom of water failing to get from the roots to the leaves of the plants. One of natures strange ironies is that trees that are dying or lack of water show the same symptoms of those that are dying from too much water. The reason is simple. In both cases the water is not reaching the leaves. Too little water and there is none to reach the leaves. Too much water and the small absorbing roots that take the water in are destroyed. They can only survive if there is oxegen available for respiration. Waterlogged soils exclude the oxegen and the roots die. Consequently not moisture is absorbed and the leaves have the same scorched syptoms that they get with sever drought injury. Larry A. Sagers Regional Horticulturist Utah State University Extension Thanksgiving Point Office