Diseases Affecting Hemp in New York

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Authors

Gary Bergstrom, Jennifer Starr, Kevin Myers, and Jaime Cummings


Infectious diseases are likely to reduce the yield and quality of hemp as this crop is grown more widely and more frequently in the same fields in New York. The cornerstone of disease management is prevention. This is accomplished by planting hemp following crops with no or few pathogens in common with hemp; purchasing viable, clean, certified seed; preparing a good seedbed on a well-drained site; sowing at recommended times, populations, and depths for optimal canopy development and weed suppression; and timely harvest and appropriate post-harvest drying, cleaning, storage and processing of grain, buds, and fibrous tissues. Currently, no fungicides are labeled in NY for control of hemp diseases. Research is being conducted to determine the efficacy of synthetic and biological fungicides that could be labeled for future seed or foliar application.

Please help Cornell assess diseases in hemp. If you observe symptoms you think may be disease, contact your local Cornell Cooperative Extension Crops Educator or the Cornell Field Crops Pathology lab: jkk26@cornell.edu or gcb3@cornell.edu


Seedrots and seedling blights

Seedrots and seedling blights are caused by seed-borne and soilborne microbes, particularly by the oomycete Pythium and fungi in the genera Fusarium, and Rhizoctonia.

image showing pythium seedling blight
Pythium seedling blight

Pythium and Fusarium species can become systemic and induce root, crown, and wilt symptoms, and reduce yield.

Pythium wilt
Fusarium wilt

Molds

White mold is a significant threat to hemp. The fungus, Sclerotinia sclerotiorum, also attacks soybean, forage legumes, and many vegetable crops and broadleaf weeds, and it survives in soil for more than 2 years. Hemp should be grown in rotation with non-host crops such as cereals, and broadleaf weeds should be suppressed.

White mold on a hemp stem
White mold on a hemp stem
White mold on a hemp stem
White mold on a hemp stem

Botrytis gray mold is the most frequently encountered disease of hemp in NY in both fields and greenhouses. It is favored by high humidity and poor airflow.

Botrytis gray mold on hemp
Botrytis gray mold on hemp
Botrytis gray mold on hemp
Botrytis gray mold on hemp

Leaf Spots

Diverse leaf spots have been diagnosed in New York in association with several fungal genera including: Bipolaris, Boeremia (Phoma), Cercospora,Colletotrichum, Cristulariella, Leptosphaerulina, Phaeomycocentropora, Septoria, and Stagonospora. Bipolaris leaf spot is a newly discovered disease in New York and Kentucky and is widely distributed and shows severe disease in some hemp varieties. We are in the process of demonstrating pathogenicity of the fungal isolates collected from hemp.

Zonate leaf spot
Zonate leaf spot
Septoria leaf spot
Septoria leaf spot
Phaeomycocentrospora leaf spot
Phaeomycocentrospora leaf spot
Bipolaris leaf spot
Bipolaris leaf spot
Leptosphaerulina leaf spot
Leptosphaerulina leaf spot
Bipolaris leaf spot
Bipolaris leaf spot

Planting resistant hemp varieties is likely to be an important control measure as we learn more about varietal reactions to the most important fungal pathogens.


Powdery mildew

Powdery mildew occurs widely in greenhouses. Biocontrol products and varietal resistance are being evaluated as future control methods.

Powdery mildew. Courtesy of N. Gauthier. http://kyhempdisease.com

Fusarium contamination

The infection of female flower buds and grains is a serious and underestimated disease as it may result in contamination by Fusarium mycotoxins. We have found contamination of hemp grain in excess of 7 ppm of deoxynivalenol (vomitoxin). A survey of New York hemp grain for mycotoxins is being conducted in 2019.

Fusarium bud blight
Fusarium bud blight
Fusarium bud blight
Fusarium bud blight
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