Silicon Soil Amendments for Suppressing Powdery Mildew on Pumpkin

A greenhouse experiment was conducted with Cucurbita pepo L. “Howden” pumpkin to compare the effectiveness of various soil amendments for providing Si nutrition, improving soil fertility, and suppressing powdery mildew (Podosphaera xanthii). A sandy loam soil with an initial soil pH of 4.5 was left unamended or amended with various liming materials or silicon sources. Calcite limestone, dolomite limestone, wollastonite, CaMg silicate slag, and wood ash were similarly effective liming materials for neutralizing soil acidity, but Montanagrow™ and glacial rock flour were not shown to be effective liming materials. Powdery mildew disease incidence and severity was visually scored on the foliage. Disease development was inversely related to Si concentration in vine tissue. Wollastonite was the most effective amendment at increasing Si uptake and for suppressing powdery mildew disease and glacial rock flour was not effective.