Foliar sprays of clay reduce the severity of powdery mildew on long English cucumber and wine grapes

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 [Sphaerothec a fuliginea (Schlech.:Fr.) Poll.] and to field-grown wine grapes (Vitis vin ifera L.) before natural inoculation with powdery mildew [Uncinula necator (Schwein.) Burrill]. In all cases, the clay sprays did not eradicate the pa thogen, but. resulted in significant reductions in disease severity. In cuc umber, a single spray of 0.5% clay reduced colony numbers on leaves by up t o 60%. Spraying after inoculation was generally more effective than sprayin g before inoculation. In grapes, repeated sprays of either 2% or 4% clay we re applied through the season to 'Reisling' and 'Chancellor' vines. Four pe rcent clay reduced the amount of leaf surface covered by mildew by 22% in ' Reisling' and 51% in 'Chancellor'. Both concentrations reduced the incidenc e of mildew on clusters and canes. No treatment effects were observed on fr uit quality. Our results demonstrate that foliar sprays of clay can reduce the severity of Sphaerotheca fuliginea and Uncinula necator on cucumbers an d grapes, respectively.