Fusarium Head Blight Of Hemp
HENRY SMITH, NICOLE GAUTHIER AND KIM LEONBERGER
LEXINGTON, KENTUCKY
Fusarium head blight (FHB) is a common disease of hemp that poses a significant threat both to cannabinoid/flower and grain producers. The disease causes severe blighting of floral tissues that can result in direct yield losses and rejection by processors. The FHB causal fungi can also potentially contaminate harvested grain and flowers with mycotoxins that are harmful to humans and livestock.
Fusarium Head Blight of Hemp Facts
- Symptoms appear once flowers develop. Interior tissues closest to the stem or tissue in compact buds are often first to show symptoms (Figure 1). Over time, extensive necrosis and blighting of individual flowers or entire heads develops (Figure 2). Affected sugar leaves may result in reduced cannabinoid yield. For grain cultivars, disease may result in premature seed drop, with affected grain being lighter in color, brittle, and the presence of black fungal bodies on the exterior of seeds (Figure 3).
- Initial symptoms of FHB can be confused with those caused by corn earworm. The presence of the insect or its frass suggests an insect issue and not disease.
- The FHB pathogens overwinter on crop residues left in the field from the previous season or on weed hosts.
- The pathogens that cause FHB have a wide host range including corn, wheat, and gramineous weeds.
- Conditions favoring disease development include periods of high moisture and humidity and temperatures between 75-85°F.
- Spread can occur by wind and water movement.
- Caused by multiple species and complexes of Fusarium.
Management Options
Field management
- Increase plant spacing or reduce seeding density to improve air circulation, lower humidity within canopies, and decrease leaf wetness (e.g., after a rain event).
- Plant cultivars with a less compact bud structure to improve air flow within heads.
- Reduce field residue prior to planting. Till to bury infected residue at least 4 inches.
- Control gramineous weeds within and adjacent to field plots throughout the season.
- Rotate away from major FHB host crops (hemp, cereals, corn) to a non-host for at least 2 to 3 years. Nonhost crops include alfalfa and vegetables.
- Currently, limited pesticides are registered for hemp in the U.S. Most registered fungicides are biological or biorational products. A list of approved products for Kentucky growers is provided by the Kentucky Department of Agriculture in the Kentucky Hemp and Pesticides publication. Studies are ongoing to identify effective biological and biorational fungicides and appropriate application timings.
- Insecticide products targeted toward corn earworm (Helicoverpa zea) may reduce wounding on buds and can potentially reduce Fusarium infections and FHB development.
Postharvest management
Causal Fusarium spp. can continue to colonize and damage floral and grain material during storage.
- Avoid harvesting diseased floral or grain material.
- Dry grain and floral material prior to long-term storage. Floral material should be dried at 60% humidity and 60°F to 70°F, and grain should be dried to 8% or 9% moisture at temperatures below 120°F.
- Remove diseased plants from storage if fungal contamination is identified.
- Avoid storage in warm or humid environments.
Additional Information
HENRY SMITH, NICOLE GAUTHIER AND KIM LEONBERGER: University of Kentucky