SUPPRESSION OF POWDERY MILDEW IN SQUASH BY APPLICATIONS OF WHITEWASH,CLAY AND ANTITRANSPIRANT MATERIALS

The incidence of powdery mildew, caused by Sphaerotheca fuliginea (Sch lecht. Fr.) Polacci, in squash plants, was suppressed in the field to 50-60% of that in untreated control plants by weekly sprays with white wash (Loven or Yalbin) or clay. Loven or Yalbin sprays resulted in sig nificant reductions in disease level, more on the adaxial (59-65%) tha n on the abaxial (38-52%) surface of leaves, and more on young (53-59% ) than on old (12-18%) leaves. The addition of 0.1% Dabak (a commercia l sticker) to the whitewashes significantly increased their efficiency (22% above that of the controls), the degree of protection being asso ciated with whitewash concentration. Squash leaves were protected from powdery mildew also by weekly sprays of the antitranspirant Vapor Gar d, to a level comparable with that achieved by a whitewash plus sticke r. However, the protection levels achieved with whitewashes, clays and antitranspirant were lower than with a fungicide (propiconazole). Exp eriments conducted under controlled conditions resulted in higher rate s of escape from infection and a lower rate of hyphal and conidial dev elopment on plants and tissues following whitewash, clay and antitrans pirant treatments.