University of Kentucky plant pathologists have identified a new disease that has the potential to be a major setback to the state’s growing hemp industry.
Plant pathologist Nicole Gauthier received her first report of the disease in southeastern Kentucky at the end of the 2014 season, the first year hemp was reintroduced into the state. Gauthier collected isolates of the fungus after the same producer reported it again in 2015.
“We struggled to identify it initially, because it is not a common fungus. There was nothing similar discussed in the old literature,” Gauthier said.

Gauthier, graduate student Desiree Szarka, and Chris Schardl, chair of Plant Pathology, have worked to confirm the fungus of this new plant disease, sequencing the entire genome of five isolates plus individual genes of five others.
“The pathogen has unprecedented genetics and a high degree of genetic variability, which could make it hard to control,” Schardl said. “This suggests that the fungus has separate, established populations throughout the region.”
The disease, called hemp leaf spot, starts as small, round spots on leaves. As the disease spreads, the leaves turn brown, dry out, and twist. The disease causes plant stunting, reduces photosynthesis and bloom size, and causes necrosis of the plant’s calyx leaves.
The amount of damage to the crop depends on when infection occurs. Producers have reported the disease as early as July 1, and such early infections can cause complete crop loss.
Disease reports have increased each year. As of 2018, the disease was identified in nine counties. Producers in five other eastern U.S. states also have reported incidences.
The lack of funding for hemp studies is slowing the necessary research, but UK plant pathologists are doing everything they can to learn how this new pathogen survives, how it overwinters, its potential hosts, whether it produces a toxin, potential biocontrol agents, and variety susceptibility.

—Katie Pratt