Unique Vapor Activity by CGA-64251 (Vangard) in the Control of Powdery Mildews Roomwide in the Greenhouse. Michael Szkolnik, Professor, Department of Plant Pathology, New York State Agricultural Experiment Station, Geneva 14456. Plant Dis. 67:360-366. Accepted for publication 27 August 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-360.

Unique and complete control of powdery mildews in 112-m³ greenhouse rooms at 21–28 C was achieved for 3 mo and longer by vapor action of CGA-64251 (Vangard) applied to cheesecloth, cotton or olefin fiber cord, or polypropylene shading cloth. The vapor inhibited spore germination and repressed mildew colonies. The powdery mildew fungi controlled in these trials were Podosphaera leucotricha (on apple), Sphaerotheca fuliginea (on cucurbits), Erysiphe polygoni (on beans and peas), Uncinula necator (on grape), S. pannosa (on rose), Oidium caricae (on papaya), and E. cichoracearum (on broadleaf plantain). The vapor phase control was highly effective in greenhouses into which outside air was introduced through vents and evaporative coolers. No phytotoxic effect of CGA-64251 vapor on exposed plants was detected. When these plants were moved from a CGA-64251-treated to an untreated room, the foliage was readily colonized by their respective mildews.