Once established, mistletoe extracts moisture and nutrients from trees. Modesto ash is the preferred host tree, but black walnut, alder, birch, box elder, cottonwood, oak, maple, locust and fruit and nut trees also are susceptible. Mistletoe has thick, green leaves nearly oval in shape. Female plants produce white, sticky berries that are especially attractive to birds. Birds eat the berries which pass through them undigested and infest other trees.
Heavy infestations weaken trees, which can eventually die.
According to information from the University of California cooperative extension, the most effective control of mistletoe is to prune it out as soon as it appears. Prune branches at least one foot below the mistletoe attachment. Mistletoe doesn't die easily and may resprout. Prune it out again, but don't severely prune or top the tree. If in doubt, call a certified arborist.