Powdery Mildew of Hemp Research Yields Valuable Insights for Growers

Interest in hemp production in Kentucky is on the rise. However, little to no information is known about the many diseases that pose a risk to hemp.

One of the most common diseases of hemp is powdery mildew. This disease occurs on leaves, buds, and other young plant tissues (Figure 1) and reduces overall plant quality. While it may be present in the field, more severe damage is often seen in greenhouse production. As fungicides are not currently an option for growers, Dr. Nicole Ward Gauthier and associates in the UK Department of Plant Pathology set out to identify cultural practices that might limit the spread of this disease.

Figure 1: Powdery mildew on hemp. (Photo: Nicole Ward Gauthier, UK)

Figure 1: Powdery mildew on hemp. (Photo: Nicole Ward Gauthier, UK)

Research Experiments

Two research experiments were conducted over the summer.

(1) In the first experiment, 22 hemp varieties from different growers across Kentucky were tested for powdery mildew susceptibility. Young plants were screened for powdery mildew. Preliminary results indicated that hemp varieties grown for cannabidiol (CBD) production had the highest incidence (occurrence) of disease. However, three fiber hemp varieties (Fibrol, Lipko, and Santica) had the highest severity (amount of disease). This variation in incidence and severity indicates the importance of variety selection to powdery mildew management.

(2) A second experiment used detached hemp leaves to study the impact of powdery mildew growth as a result of changes in environmental conditions. Powdery mildew is known to thrive in shady areas at temperatures between 59-77°F. In addition, the use of red LED light (650 nm) has been shown to have efficacy against powdery mildews affecting other plants. Changes in temperature and light conditions were used to determine the effect on powdery mildew of hemp. Infected leaves were exposed to red LED light (Figure 2) and evaluated for disease development. Further research is needed in this area to determine whether manipulation of lighting can be used by growers to prevent or reduce powdery mildew in greenhouse hemp.

Figure 2: Detached hemp leaves infected with powdery mildew in a growth chamber with red LED light. (Photo: Kimberly Leonberger, UK)

Figure 2: Detached hemp leaves infected with powdery mildew in a growth chamber with red LED light. (Photo: Kimberly Leonberger, UK)

Additional Information

 

By Kimberly Leonberger, Extension Associate; Angelina Bernardini and Justin Judy, Research Interns; and Nicole Ward Gauthier, Extension Plant Pathologist

 

 

 

Posted in Hemp