Question
Hello, I have a 5 year old river birch which appears very healthy, but I see ants around the base and some crawling up the tree.  Should I be concerned.

Answer
They are more than likely tending the aphids on the tree. Aphids suck the plant juices from the plant and secrete a sticky substance called honeydew. If there are many aphids you should see of feel the sticky on the leaves. Any of the any bait type insecticides should kill the ants. If there is  sticky on the leaves you may want to spray the tree with an insecticide for aphids. Check with your local nursery for a systemic insecticide for aphids. One of the newer ones can be applied to the soil and taken up by the tree to kill the aphids. If there is no sticky then there are few aphids and controlling the ants will be all that is needed.