Foliar Sprays of Clay Reduce the Severity of Powdery Mildew on Long English Cucumber and Wine Grapes

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  • 1 Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, P.O. Box 1000, Agassiz, BC V0M 1A0, Canada
  • 2 Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada
  • 3 Pacific Agri-Food Research Centre, Agriculture and Agri-Food Canada, Highway 97, Summerland, BC V0H 1Z0, Canada
  • 4 Inland Machinery Manufacturing, 205, 20381-62 Avenue, Langley, BC V3A 5E6, Canada

Foliar sprays of a nonswelling chlorite mica clay were applied to leaves of greenhouse-grown long English cucumber (Cucumis sativus L.) plants, either before or after an artificial inoculation with powdery mildew [Sphaerotheca fuliginea (Schlech.:Fr.) Poll.] and to field-grown wine grapes (Vitis vinifera L.) before natural inoculation with powdery mildew [Uncinula necator (Schwein.) Burrill]. In all cases, the clay sprays did not eradicate the pathogen, but resulted in significant reductions in disease severity. In cucumber, a single spray of 0.5% clay reduced colony numbers on leaves by up to 60%. Spraying after inoculation was generally more effective than spraying before inoculation. In grapes, repeated sprays of either 2% or 4% clay were applied through the season to `Reisling' and `Chancellor' vines. Four percent clay reduced the amount of leaf surface covered by mildew by 22% in `Reisling' and 51% in `Chancellor'. Both concentrations reduced the incidence of mildew on clusters and canes. No treatment effects were observed on fruit quality. Our results demonstrate that foliar sprays of clay can reduce the severity of Sphaerotheca fuliginea and Uncinula necator on cucumbers and grapes, respectively.

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