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Air Pollution Toxicity to Eastern White Pine in Indiana and Wisconsin. Roland W. Usher, Biologist, The Institute of Ecology, Indianapolis, IN 46208. Wayne T. Williams, Plant Pathologist, The Institute of Ecology, Indianapolis, IN 46208. Plant Dis. 66:199-204. Accepted for publication 1 May 1981. Copyright 1982 American Phytopathological Society. DOI: 10.1094/PD-66-199.

Air pollution disease was widespread on eastern white pine (Pinus strobus) in Indiana, affecting tolerant as well as sensitive genotypes. Tip necrosis of needles was more prevalent than needle flecking and chlorotic mottling, but both symptom types were considered primary manifestations of air pollution disease. Premature needle abscission was widespread and more common in areas with severe disease. Abscission was not as closely associated with overall disease severity as other symptoms, including chlorotic mottling and flecking, percentage of needles with tip necrosis, and length of necrosis; all of these symptoms correlated with disease severity better than abscission, according to linear regression analyses. A disease index composed of these four components reflected changes in disease severity from 1979 to 1980 and within and among study sites. Significant differences in disease severity between 1979 and 1980 corresponded to significantly different air pollution loads in 1978 and 1979. Changes in frequency distribution of the principal index components are discussed in relation to changes in disease severity along a gradient of differing pollution concentrations and durations. Ozone concentrations and durations of episodes were sufficient to elicit phytotoxicity numerous times each growing season in the region. Sulfur dioxide concentrations considered to be phytotoxic were also common at urban sites and rural areas downwind from coal-fired power plants. Toxicity on trees in south central Wisconsin was compared with that on Indiana trees.