Evaluation of a Roadside Survey Procedure for Dwarf Mistletoe on Ponderosa Pine in Colorado. Laura M. Merrill, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, USDA Forest Service, 240 W. Prospect, Fort Collins, CO 80526. Frank G. Hawksworth, Plant Pathologist, Rocky Mountain Forest and Range Experiment Station, USDA Forest Service, 240 W. Prospect, Fort Collins, CO 80526; and David W. Johnson, Supervisory Plant Pathologist, USDA Forest Service, Rocky Mountain Region, Timber, Forest Pest, and Cooperative Forestry Management, 1117 W. 8th Ave., Lakewood, CO 80225. Plant Dis. 69:572-573. Accepted for publication 8 January 1985. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1985. DOI: 10.1094/PD-69-572.

A survey of dwarf mistletoe intensity on ponderosa pine (Pinus ponderosa) was conducted along roadsides and on adjacent plots in the Roosevelt, Pike, and San Juan national forests in Colorado. Presence of dwarf mistletoe (Arceuthobium vaginatum subsp. cryptopodum) was recorded along roads for each 0.1 km of a strip one chain (20 m) wide and 1.6 km long. Plots were then established at 100-m intervals 40 m from and parallel to the same surveyed portion of the road. Regression of plot data on roadside data was highly significant (R² = 0.88 for all national forests combined). The roadside survey procedure can be reliable for estimating the proportion of ponderosa pine stands with dwarf mistletoe if the road network provides a representative sample of the stands being surveyed.