Effects of Bicarbonates and Film-Forming Polymers on Cucurbit Foliar Diseases. O. Ziv, Agricultural Research Organization, The Volcani Center, Israel. T. A. Zitter, Cornell University, Ithaca, NY 14853. Plant Dis. 76:513-517. Accepted for publication 9 December 1991. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0513.

The inhibitory effects of sodium, potassium, and ammonium bicarbonates (NaHCO₃, KHCO₃ and NH₄HCO₃, respectively) alone and in combination with SunSpray Ultra-Fine Spray Oil (SS) on powdery mildew, caused by Sphaerotheca fuliginea; gummy stem blight, caused by Didymella bryoniae; Alternaria leaf blight, caused by Alternaria cucumerina; and Ulocladium leaf spot, caused by Ulocladium cucurbitae, were studied. SS oil performed consistently better than ForEverGreen, Masbrane, Crop Life, Vapor Gard, Nu-Film 17, and Bio-Film for powdery mildew control in cucumber and pumpkin. NaHCO₃ or KHCO₃ combined with SS oil, both at 0.5%, were more effective treatments for powdery mildew on pumpkin than either of the materials used alone, whereas NH₄HCO₃ was ineffective. All three bicarbonates (1% w/v) plus SS oil (1% v/v), and especially NH₄HCO₃ + SS, provided good control of gummy stem blight and Alternaria leaf blight of muskmelon and Ulocladium leaf spot of cucumber in greenhouse trials. The bicarbonate-plus-oil treatments were more effective when applied prior to inoculation. KHCO₃ was phytotoxic to mildew-infected pumpkin leaves at concentrations greater than 0.5%; NaHCO₃ caused minimal injury, and NH₄HCO₃ caused no injury. Similar results were obtained when bicarbonate solutions were applied to punctured cucumber cotyledons. In vitro studies showed that bicarbonate salts inhibited growth of these organisms and Colletotrichum orbiculare, causal fungus of cucurbit anthracnose. NH₄HCO₃ was most inhibitory. Na, K, and NH₄ chloride salts were least inhibitory.

Keyword(s): antitranspirants, disease control, mineral oil.