By Jeff Floyd
Certified horticulturist and arborist
Like parasites such as fleas, ticks and most fungi, mistletoe takes nutrients from trees and gives back nothing in return. Once a mistletoe seed lands on a branch, it sends a root-like projection called haustoria, several inches straight into the veins of its host tree. Once established, mistletoe can become very aggressive having access to the tree’s resources and the capability of producing its own carbohydrates.
At this point, it becomes extremely difficult to eliminate it. While it can be removed from small branches and twigs, mistletoe is virtually impossible to remove, especially from the lower section of the trunk unless you plan on cutting down the entire tree.
Research with at least one plant growth regulator, known as ethephon, has shown that it can be suppressed but it does not kill it. Herbicides such as RoundUp® may damage mistletoe, but none have successfully killed it without killing the tree too. Other research has demonstrated that mistletoe will eventually regrow from the haustoria deep in the vascular system even after pruning out the plant and covering the area with black plastic for up to three years.
Since mistletoe can steal enough nutrients from severely infested branches to kill them, it should be removed when possible. First, the visible portion of the plant should be carefully removed. Bagging before removal when possible, may reduce the spread of seeds. Mistletoe is a brittle plant, breaking apart easily when disturbed. This allows its seeds to land on other branches and get a foothold. However, bagging is not a practical solution for most people.
The haustoria will grow as much as a foot or more into the vascular system just under the bark. Pruning infested branches back to a joint at least a foot to eighteen inches from the parasite’s origin is a reasonable method of eliminating it from a branch. Vigilantly breaking it off an infested trunk is the most reasonable way to keep it at bay there. However, mistletoe will pop out at new places of origin on the trunk as its roots travel and spread nearby through the vascular system.
Whatever method is used, lessening the amount of mistletoe in a tree will improve its chances of a longer life. Mistletoe robs trees of valuable nutrients, negatively impacting their overall health, especially in times of drought, freeze and exposure to herbicides commonly used in the lawn.
