Leafy mistletoe doesn't kill host trees
Myths surround the subject of mistletoe because individuals differ in thought about the unique association between the plant and its hosts. Two myths related to plant health are that leafy mistletoe kills trees and it affects only weak trees. Both are false. If leafy mistletoe killed its host, it, too, would die.
I’ve microscopically examined where the root-like tissues of mistletoe joined the tree’s conductive tissue, and no cell damage was found. Connections of water-conducting xylem tissues of both species were examined. Host trees provide water and water-soluble nutrients, but not carbohydrates. Mistletoe is a green plant and manufactures its own food. It’s a parasite but not a pathogen. Normal function of a tree provides more than enough moisture and nutrients without endangering its own health.
Individuals who observe mistletoe growing on hackberry trees in fencerows may be inclined to believe that infestation occurs only on weakened trees. Such trees suffer from shade, water and nutrient deficiencies because of intense competition. Water and nutrient use by mistletoe is minimal when compared to what is used by the tree.
Only leafy mistletoe types occur in Texas. Several species exist, however, and this accounts for different tree species being affected. Mesquite, elm and hackberry are among the most commonly affected in this area.
Dwarf mistletoe affects coniferous plants, including pine. It is different in appearance from leafy mistletoe and doesn’t occur in Texas. Unlike leafy mistletoe, it’s a pathogen and damages infected trees.
Birds are effective in the distribution of leafy mistletoe seed. Female plants produce white, seed-containing berries that are a food source for birds. Their systems digest the pulpy fruit portions, but not seed. When deposited on tree limbs, seeds germinate and root tissue penetrates and grows into conductive tissue. Male mistletoe plants produce pollen to fertilize female mistletoe flowers. Male plants typically outnumber female plants.
Leafy mistletoe should be controlled when and if tree owners find its presence undesirable. It’s seldom a matter of concern during the active growing season, but its presence stands out on deciduous trees during the dormant season.
Pruning is effective in mistletoe removal. One should make cuts well below points of attachment on smaller limbs. Allowing mistletoe root-like conductive tissues to remain results in regrowth. Cutting 1 foot below the point of attachment is adequate. When and if it becomes desirable to remove mistletoe from large limbs, one should use a wood chisel to remove mistletoe root tissue. Don’t remove enough wood to weaken the limb, however.
A mistletoe control product is available locally. “Florel” is FDA approved and is available at certain stores. The active ingredient is ethylene. That’s the same compound that’s used to ripen green bananas and tomatoes. It should be used only during the dormant season. It has been tested locally. A second application may be required during the following dormant season if regrowth occurs.
Mistletoe control is optional. Remove it mechanically or chemically if you want your trees to be free of the condition. It’s your choice.
• Wendell Horne is a retired Texas A&M University plant pathologist and consultant. His e-mail address is