Growth Retardation of Plantation-Grown Sugar Pine byLophodermella arcuata

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Abstract
L. arcuata defoliated 20-yr old saplings of sugar pine (P. lambertiana) in a 16-ha plantation in California [USA]. Only the current season''s needles remained on severely infected trees by Oct. of each year. In 1972, when the infestation was first observed, only 2 adjacent trees were infected; but by 1974 and 1975, the pathogen had infected most trees over areas of 4.2 ha and 12.6 ha, respectively. Disease severity was estimated each year (1974-1977) as the number of fascicles per tree with at least one infected needle (needles brown, hysterothecia visible). There were significant interactions between terminal growth and disease class and between radial growth and disease class. That is, the magnitude of growth was not independent of disease class. Pertinent orthogonal comparisons revealed that radial and terminal growth of diseased trees was significantly less than growth of healthy trees. During years of rapid disease spread (1974-1977), radial and terminal growth of diseased trees decreased annually, while there were no significant between-year differences in annual growth of healthy trees. Apparently there was no terminal growth reduction attributable to drought effects, but average radial growth of healthy trees for 6 yr before the drought was significantly greater than average growth during the 3 yr of the drought.

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