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    Author(s): George T. Ferrell
    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
    Publication Series: Research Paper (RP)
    Station: Pacific Southwest Research Station
    PDF: View PDF  (876 KB)


    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.

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


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

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