Response of Common Milkweed to Oxidant Air Pollution in the Shenandoah National Park in Virginia. S. F. Duchelle, Graduate Research Assistant, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. J. M. Skelly, Professor of Plant Pathology, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg 24061. Plant Dis. 65:661-663. Accepted for publication 7 February 1981. Copyright 1981 American Phytopathological Society. DOI: 10.1094/PD-65-661.

The effects of ambient doses of ozone on Asclepias syriaca, common milkweed, were determined in twelve 10-ft-diameter plots in the Big Meadows area of the Shenandoah National Park in Virginia. Chlorosis and purple stippling on the adaxial leaf surface were observed on milkweeds grown in ambient air chambers and open plots; those grown in charcoal-filtered air were asymptomatic and taller than those in other treatments. In the laboratory, ozone at 0.05, 0.10, and 0.15 ppm for 6 hr/day for 7 days induced symptoms identical to those observed in the field.