Introduction

In 2013, a combined road and plot survey of dwarf mistletoe and comandra blister rust diseases was conducted of lodgepole pine stands in the Bighorn National Forest. Variable-radius plots (n=91) were installed at two-mile intervals along roads to evaluate lodgepole pine for these diseases. Plot survey results estimate 42% of lodgepole pine trees and 65% of the plots near roads were infected with dwarf mistletoe; 10% of the trees and 37% of the plots were infected with comandra blister rust; and 5% of the trees and 23% of the plots had both diseases. Road side survey results of 161 miles of road, broken into 0.1 mile sections found 75% of the sections had dwarf mistletoe, 44% had comandra blister rust, and 36% had both diseases. Previous surveys in the forest indicated increasing levels of dwarf mistletoe incidence. The 2013 survey suggests a slight decrease in road, but an increase in plot dwarf mistletoe incidences. Comandra blister rust disease incidence decreased using both methods compared with previous surveys. Emphasis on suppression work for these two diseases will result in reductions in disease incidences and promote improved forest health. Introduction Lodgepole pine dwarf mistletoe (Arceuthobium americanum) is one of the most important diseases in lodgepole pine (Pinus contorta) stands. It is a parasitic plant that requires water, mineral, and carbon nutrients from its hosts. This stresses host trees causing reductions in both growth and cone/seed production. Infections of young host tissues result in stimulation of dormant host buds which causes abnormal-dense clumps of branches called “brooms” or “witches’ brooms.” Other symptoms include branch swellings, host dieback from the top down, and eventual tree mortality. Trees can survive infection for decades. However, in areas with extensive infection tree mortality can be three to four times higher than in uninfected areas (Hawksworth and Wiens 1996). Comandra blister rust (Cronartium comandrae) is also one of the more important diseases of lodgepole pine in the region. This fungal rust disease causes stem deformities, growth reduction, and cankers that girdle branches or stems resulting in top-kill and tree mortality. Trees may survive several decades with spiked-tops. Heavy stand infections can result in high volume losses by affecting tree form, lumber quality, and growth rate. Past road-plot surveys conducted on the Bighorn National Forest (NF) indicated an increasing incidence of dwarf mistletoe in lodgepole pine. In 1958, Hawksworth (1958) reported 31% of road sections of 146 miles of roads through lodgepole pine stands in the Bighorn NF were infected with dwarf mistletoe. Twenty years later, Johnson et al. (1979) duplicated the methodology used in the road plot studies. The same roads were evaluated as in the Hawksworth survey, including newer roads built through lodgepole pine stands. Johnson et al. (1979) found 36% of 174 miles through lodgepole pine forest types near roads were infected with dwarf mistletoe. After another 20 years (sampled in 1999) Harris (2003) found 79% of the trees along 147 miles were infected with dwarf mistletoe.