Pacific Southwest

Title: Growth of white firs defoliated by Modoc budworm in northeastern California

Author: Ferrell, George T.

Date: 1980

Source: Res. Paper PSW-RP-153, Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p

Station ID: RP-PSW-153

Description: Open-grown, pole-sized white firs defoliated by Modoc budwonn (Choristoneura viridis) in northeastern California in the years 1959-62 and 1973-75 suffered only minor growth reductions and topkilling compared with the effects that more protracted budworm outbreaks have had elsewhere on their conifer hosts. Growth index analysis indicated that the firs averaged a cumulative height growth deficit of 14.5 percent, or 34 cm (1.1 ft), over both outbreaks. Firs heavily defoliated during the 1973-75 outbreak were more frequently topkilled and consequently suffered larger height growth deficits. Topkilling during both outbreaks, however, was limited to the terminal shoot, resulting in slight crooks or forks, but no decay, in the stems. Radial growth deficits attributable to the outbreaks were not found and, unless future outbreaks are more protracted or otherwise intensify, the Modoc budworm can be considered only a marginal economic pest of firs in California.

Keywords: Modoc budworm, Choristoneura viridis, white fir, Abies concolor, defoliation effects, growth, injury

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Citation

Ferrell, George T.   1980.  Growth of white firs defoliated by Modoc budworm in northeastern California.   Res. Paper PSW-RP-153, Berkeley, CA: Pacific Southwest Forest and Range Experiment Station, Forest Service, U.S. Department of Agriculture; 9 p.