Suppression of Hemp Powdery Mildew Using Root-Applied Silicon

Powdery mildew (Golovinomyces spadiceus) is the most common disease of greenhouse cannabis. Most hemp grown for cannabinoid production is propagated by cuttings or started from feminized seed in greenhouses and then moved outdoors, while most marijuana and some hemp are grown entirely indoors. To determine the effects of silicon on powdery mildew in the green-house, silicon was applied to hemp roots in a peat-based soilless mix and evaluated for plant uptake and disease suppression over a 6-week period. This study confirmed that there was a negative linear relationship between percent silicon accumulation in leaf tissue and the percent powdery mildew per leaf area. Mildew severity in the upper canopy was significantly reduced at 300 kg/ha of silicon, while 600 kg/ha was needed for the mid canopy. Results confirmed that silicon may be a useful tool for the integrated management of powdery mildew. As the cannabis market expands, silicon can serve as a viable option for greenhouse growers, especially for plants grown in soils or soilless mixes low or limiting in soluble silicon.