Question
I have a willow tree which has been in by backyard for 4 years, about four days ago I started to notice the leaves turn yellow and they started falling off.  The branches are colored black at some spots, but for the most part green.  I talked to a nursery near by they told me to water it more and to add a fertilizer with nitrogen in it.  They recommended a there own particular brand.  Is there anything else I can do?

Answer
I would say water may be the main thing. Willows like water and require more than the average tree species. I would water with 1 inch of water --place a pan under the tree and turn the sprinkler on and when the pan has 1 inch of water in it stop. Do this every 4th day for about a 2 weeks then once a week. IF you have not done so mulch around the tree with not more than 3 inches deep of organic mulch not plied up on the trunk. This will help hold moisture around the roots.

IF the black on the branches is sticky you may also have an insect problem. There are a couple of insects that suck the plant juices from the plant and secretes a substance called honeydew which is high in sugar content and sticky. A sooty black mild will grow on this honeydew. IF the branches and/or leaves are sticky treat the tree with an insecticide called Bayer Advanced Tree and Shrub Insect control. This is applied to the soil around the tree and the roots will carry it to the leaves and twigs and when the insects suck the plant juice they are killed. Check with your local garden type store for this product. Here is a web link to the product.

http://www.bayeradvanced.com/tree-shrub-care/products/12-month-tree-shrub-insect...