INJURY TO GRAPES by Los Angeles type (photochemical) smog was recognized as early as 1957. The component of this mixture which causes the most damage is ozone. A “stipple” condition of leaves characterized by small brown areas of dead cells develops where smog is heavy, usually in May or early June. As the season progresses these leaves turn bronze and drop. Some conifers develop a yellow mottle on the needles which progresses, with continued exposure to ozone, to severe chlorosis and defoliation. Citrus may develop irregular-shaped brown to black spots on the upper leaf suface.

This work was supported in part by the California Wine Advisory Board, the Cucamonga Winery co., San Bernardino County, Kaiser Steel Co., Fontana, and Sunkist, Inc.