Question
we live in payson arizona, elevation 5,000ft.  planted willow tree about 20 years ago, has done well until last couple of years.  large branches dead, more each year.  can see small holes like eraser head size usually in a straight line and others in lines of rectangle shapes.  looks like some kind of bug, but what? and what to do?  hate to get rid og tree after all these years. leaves also dont seem to be as large and full as other years either.  thank you for your assistance.

Answer
I do not think you have an insect issue. Borer damage either has sawdust near the hole or the bark around the hole is dark due to moisture and/or the bark is loose around the damaged area.  But it does sound like it maybe under stress and this can attack borers.

The hole in lines or a pattern are from a woodpecker called a sap sucker. The bird makes the holes and the tree exudes a little sap and insects come to feed on the sap. The bird returns and eats the insects. Spray the area with  a general type insecticide and this will kill the insects feeding on the sap and the bird will not return. Use any household insecticide like Malathion, Sevin, or Bug B Gone ant spray.

I would also fertilize the tree with 10-10-10 fertilizer at the rate of 1 lb per inch of trunk diameter scattered around the tree and watered in good, apply the fertilizer just before a rain storm and you will not need to water. This will increase the health of the tree. Willow trees use a great deal of water so during dry spells if you can you may want to water the tree with 1 inch of water per week--place a pan under the tree and turn  the sprinkler on and when the pan has 1 inch of water in it stop.