Control of Dwarf Mistletoe in a Heavily Used Ponderosa Pine Recreation Forest at Grand Canyon, Arizona

Lightle, Paul; Hawksworth, Frank

Southwestern dwarf mistletoe (Arceuthobium vaginatum subsp. cryptopodum (Engelm.) Hawks. & Weins) has long been known as a serious disease of ponderosa pine (Pinus ponderosa Laws.) on the South Rim of Grand Canyon, Arizona, where mortality caused by this disease was recorded before the turn of the century (MacDougal 1899). Concern about the dwarf mistletoe situation along the South Rim was expressed by the National Park Service as early as 1933. The severity of the infestation was noted by Gill (1940,1946) and Mielke (1945), and National Park Service personnel were becoming increasingly concerned over the impact that dwarf mistletoe was making in the ponderosa pine stands east of Grand Canyon Village. Severe mortality in pole-sized and mature pines was occurring and the growth of trees in all size classes was seriously affected. However, a factor of even more consequence to the esthetics of the area was the observation that in some places, the ponderosa pine type was being replaced by Gambel oak (Quercus gambelii Nutt.). In August 1947, at the request of the National Park Service, Division of Forest Pathology personnel- met with Park Service personnel to review the situation on the ground. As a result of this meeting the Division of Forest Pathology was requested to make a preliminary study to determine (1) the need for, and feasibility of, control and (2) the general procedures to be followed if control was to be practiced. The survey was made in the fall of 1947 and the results summarized in a report by Gill (1949).