Strategies and Treatments for Leafy Mistletoe (Phoradendron tomentosum [DC.] Engelm ex. Gray) Suppression on Cedar Elm (Ulmus crassifolia Nutt.)

Abstract

Leafy mistletoe, Phoradendron tomentosum (DC.) Engelm ex. Gray, can adversely affect trees growing in urban environments. The efficacy of several methods for controlling P. tomentosum in Ulmus crassifolia was evaluated in two separate trials. In the first experiment, eight treatments with five replicate trees, 20.3 to 30.5 cm (8.1 to 12.2 in) dbh, were evaluated. Removal of the branch 30.5 cm (12.2 in) below the mistletoe, removal of mistletoe, and treating the branch bark with naphthaleneacetic acid (NAA) or a caulking compound in which mistletoe was removed resulted in reduced regrowth of the ectophyte (>90%) after 5 months. The use of growth regulator and herbicides (ethephon, 2,4-D, and glyphosate) on intact mistletoe plants in experiment 1 did not provide acceptable control of mistletoe. After 29 months, only removal of the branch and caulking over the bark after mistletoe removal demonstrated a significant long-term effect on mistletoe mortality (40% and 57%, respectively). In the second experiment, a new treatment was evaluated based on the results from the first experiment. The use of NAA and light exclusion (black latex paint) reduced the resprouting of mistletoe by 50% after 8 months, but this effect diminished over time. However, 16 months after application, NAA and paint significantly reduced regrowth compared with removing mistletoe alone. This study provides strategies to achieve acceptable short-term control and long-term management of leafy mistletoe in urban trees.