Pythium Crown and Root Rot of Industrial Hemp

The 2018 U.S. Farm bill changed the Controlled Substances Act and legalized cultivation of industrial hemp in the United States. In Arizona, the AZDA issues licenses and regulates the production and processing of industrial hemp. In 2019, 165 growing licenses and 43 nursery licenses were issued across the state, resulting in the planting of 5,430 acres in 13 counties. The University of Arizona, Extension Plant Pathology Laboratory, in Tucson has detected several major diseases in hemp crops grown during the 2019 – 2020 seasons. In this publication we will describe one such disease, Pythium crown and root rot. This disease has been observed in hemp grown with plastic mulch film and saturated heavy soil, and is associated with over-irrigation, poor drainage, and high temperatures. Pythium crown and root rot does not appear to be isolated to Arizona, and also has been reported in field-grown hemp in North Carolina, Indiana, California, and Nevada.