Question
Hello, Jim.  I live in Riverside, California, which is 75 mile east of downtown Los Angeles, on the edge of the desert.  I have a weeping willow tree that has been growing in my yard for about 15 years.  I have two questions.  First, the roots of the tree are popping out of the surface of the ground.  They are quite large.  Can the be cut out without injuring the tree?  Second, carpenter ants make a home in the tree every summer, and I have noticed that they are killing parts of the tree.  What would you suggest to get rid of the ants?  It has been a very hot summer, and the top 2/3rd's of the tree appear to be dead. I am not sure if it because of the weather or the ants.
Thank you in advance!
Sean

Answer
Cutting the roots will damage and or kill the tree.

Carpenter ant nests are very common inside trees, especially older trees that are hollow or have a significant amount of dead limbs and branches. The nests are usually in rotted, decayed wood, although some nests may extend into sound heartwood in the center of the tree.

Carpenter ants in trees are not directly harmful to the tree. Control is not essential for the tree's health, as the ants are only taking advantage of an existing situation of soft, weak wood in which to establish their colony. Stress, mechanical injury, environmental conditions, disease or other insects are responsible for killing limbs or sections of the trees in which the ants are able to nest. Once injury has occurred, wood decay can set in if moisture is present; it is the wood decay that gives the carpenter ants the opportunity to colonize the tree. Carpenter ants use knots, cracks, holes and old insect tunnels to gain access to these areas.

Control of carpenter ants inside trees is difficult but can be done as a way to reduce invasion of the ants into adjacent structures. It is also possible for ant colonies located inside trees to form satellite colonies inside a nearby home wall. Available controls are not likely to permanently rid a tree of carpenter ants so retreatment every year or so may be necessary. Dust insecticides (such as Sevin or rotenone) labeled for use on trees in the landscape are suggested for control. Apply the dust directly into the nest cavity.