Phoradendron - Management

Management

Leafy mistletoe can adversely affect trees growing in urban environments and in forests. Although mistletoe is photosynthetic, it is an obligate, semi-parasitic evergreen plant that infects host plants to derive support, water, and essential elements. They are considered a nuisance in urban environments because of their appearance on deciduous trees during winter. Severe colonization of mistletoe in individual trees can adversely affect their health. Add mistletoe to a plant stressed by urban living and the result may be death for the host plant.

Control operations include affected watering trees to improve vigor and tolerance of the infestation, sanitizing the environment by removing infected trees, branches, and aerial shoots. Pruning infected branches is not generally sufficient, the hastoria are throughout the tree by the time infestation is noted. If desired, aerial shoots can be knocked off but generally the mistletoe quickly resprouts, some benefit is derived from annual removal because it reduces seed production and spread of mistletoe to nearby plants.

Removing the shoots does not eliminate the mistletoe infection but does reduce damage resulting from its reproduction. Covering infected branches with tarpaper, roofing tar or creosote has not proven to be effective, nor is it an attractive method. These treatments work by prohibiting photosynthesis of the haustorium by opaque coverings preventing light absorption. Perhaps the best way for discouraging additional bird-dispersal of mistletoe seeds is with branch pruning or shoot removal, since it is often the mistletoe fruit that initially attracts the birds. Given the modest damage and slow rate of increase of these mistletoes, these methods are usually sufficient.

After seeds germinate, they produce haustoria that penetrate the host to extract water and minerals. This endophytic portion results in a challenging control problem because treatments must kill the outer ectophytic portion of the plant as well as the endophytic portion without damaging the host.