First Report of Hemp Leaf Spot Caused by a Bipolaris Species on Hemp (Cannabis sativa) in Kentucky

Abstract

Upon reintroduction of hemp (Cannabis sativa) in 2014, reports of a leaf spot disease became increasingly common in Kentucky. Outdoor-grown plants became severely affected with necrosis and blight symptoms, and many crops were rejected by processors either as a result of leaf and bud necrosis or as a result of reduced levels of cannabidiol. Morphological data and sequences of ITS and partial 28S rDNA identified the pathogen as Drechslera gigantea. Phylogenetic analysis grouped all isolates in a clade within Bipolaris. Dicot and monocot weed hosts within symptomatic fields were also identified. We refer to the disease as Bipolaris leaf spot, but the common reference is hemp leaf spot. This is the first report of a Bipolaris pathogen infecting C. sativa. Widespread distribution, disease severity, and extreme yield losses makes this one of the most important diseases of hemp in Kentucky.