Ozone Needle Mottle of Pine in Southern California

Abstract

The specific type of chlorotic mottling in ponderosa pine needles, as reported by various workers,^1,8,9 justifies the assumption that X-diesase, needle dieback, chlorotic decline, and ozone needle mottle in various pine species described in this paper are one and the same disease. Experimental production of chlorotic needle mottling in ponderosa pine (Pinus ponderosa Laws) with ozone-polluted ambient air and with synthesized ozone by Miller⁸ further justifies this basic assumption. Controlled fumigation studies (1959 and 1960 at the Citrus Research and Agricultural Experiment Station, Riverside, Calif.)¹⁵ confirm needle mottle of pine as a distinctive physiogenic disease, and atmopheric ozone as the prime etiological factor. Basic experimental research together with the wide range of field studies and observations by the present authors^10,15 have clarified the type and sequence in symptom expression essential for diagnosis, and have greatly extended the range of pine species visibly susceptible to atmospheric ozone. Additional emphasis is placed on significance both of the ozone needle mottle problem and of ozone as an economic factor in forestry.