Pruning: You can remove the infected branches depending on the size of the tree and number of branches to be pruned. If you have an entire tree that is severely infected with mistletoe, you can cut down the entire tree. You can also cut off the mistletoe from the branch before the seeds are set to help reduce new infections originating from the seeds. But the mistletoe will regrow after being pruned so trimming the mistletoe will only help prevent the mistletoe from spreading further in the tree or to other trees.
Chemicals: There are some chemical sprays that can be used to control mistletoe in dormant host trees. The tree must be dormant because if chemical is used on trees with leaves present, there is risk of killing the tree. A chemical spray is again only a temporary control because the mistletoe will regrow from the infected site. Remember when using any chemicals to be very careful handling and read the labels for instructions.