Suppression of powdery mildew in squash by applications of whitewash,clay and antitranspirant materials

The incidence of powdery mildew, caused bySphaerotheca fuliginea (Schlecht. Fr.) Polacci, in squash plants, was suppressed in the field to 50–60% of that in untreated control plants by weekly sprays with whitewash (Loven or Yalbin) or clay. Loven or Yalbin sprays resulted in significant reductions in disease level, more on the adaxial (59–65%) than 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 commercial sticker) to the whitewashes significantly increased their efficiency (22% above that of the controls), the degree of protection being associated with whitewash concentration. Squash leaves were protected from powdery mildew also by weekly sprays of the antitranspirant Vapor Gard, to a level comparable with that achieved by a whitewash plus sticker. However, the protection levels achieved with whitewashes, clays and antitranspirant were lower than with a fungicide (propiconazole). Experiments conducted under controlled conditions resulted in higher rates of escape from infection and a lower rate of hyphal and conidial development on plants and tissues following whitewash, clay and antitranspirant treatments.