PREDICTING THE INCIDENCE OF COMANDRA BLISTER RUST ON LODGEPOLE PINE -SITE, STAND, AND ALTERNATE-HOST INFLUENCES

Incidence of cankers caused by comandra blister rust (Cronartium coman drae) on lodgepole pine (Pinus contorta) and distribution of the rust' s alternate host, pale comandra (Comandra umbellata subsp. pallida), w ere mapped in portions of two Wyoming forests. Rust incidence in 24 st ands in the Shoshone National Forest varied from 14 to 64%, and rust i ncidence in 190 plots in the Medicine Bow National Forest ranged from 0 to 36%. Comandra populations occurred on open, upper slopes surround ed by lodgepole pine stands in the Shoshone study area and on dry ridg e tops along the eastern and western slopes of the Medicine Bow study area. Simulations of wind speed and direction during periods favorable for basidiospore dispersal were used to identify comandra populations upwind of surveyed lodgepole pine stands. Rust incidence was highest in stands older than 40 yr along forest edges adjacent to comandra but also was high in some stands 1-10 km downwind of likely inoculum sour ces. Rust incidence was significantly negatively correlated with dista nce to comandra and with stand density and was significantly positivel y correlated with average tree diameter, height, and age. Expected inc idence of comandra blister rust across surveyed portions of the two fo rests can be predicted from average tree height or diameter and distan ce to comandra.