Multiple Diseases Found On Hemp

The heavy rain events and somewhat cooler temperatures prior to this week’s heatwave increased disease pressure in hemp. This will be the first growing season we have observed downy mildew on hemp at Meigs farm. It was identified in the cannabinoid cultivar trial on many cultivars.

Downy mildew thrives when temperatures are cooler, there is high humidity, and free water.

Growers should look for greenish-yellow, water-soaked lesions on the tops of leaves. These lesions will progress and turn brown. A gray to black fuzzy appearance can be observed on the underside of leaves where the lesions are. Growers should avoid scouting in the early morning or after rain. Remove leaves with downy mildew can and place in a paper bag. Avoid leaving infected plant tissue on the ground. This will reduce inoculum for the following growing season.

It is unclear the economic impact of downy mildew in hemp. However, this pathogen can be devastating in other crops.

White mold was also found in the cultivar trial at Meigs farm. Day-neutral cultivars were the most affected, likely due to early flowering and dense floral structures. Growers should look for browning on the leaves and the floral tissue. A fluffy white appearance (mycelial growth) is found along the stem. We also observed black overwintering structures (sclerotia) on the stem.

There are several fungicides available for hemp growers in Indiana. While there are quite a few products registered through EPA, not all of them are registered in Indiana. Products need to include hemp on the label or supplemental label to be used. Growers can find the list of products can at https://www.oisc.purdue.edu/pesticide/pdf/pest_hemp_product_list.pdf. Supplemental labels can be found at https://www.oisc.purdue.edu/pesticide/index.html under the Pesticide Use in Hemp section.

 

Downy mildew lesions on upper surface of hemp leaf.

Downy mildew lesions on upper surface of hemp leaf.

 

Underside of lesions.

Underside of lesions.

 

Browning of tissue caused by white mold.

Browning of tissue caused by white mold.

 

White mold with sclerotia on hemp stem.

White mold with sclerotia on hemp stem.

Share This Article
It is the policy of the Purdue University that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue is an Affirmative Action Institution. This material may be available in alternative formats. 1-888-EXT-INFO Disclaimer: Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current directions of the manufacturer.
Pest&Crop newsletter - Department of Entomology Purdue University 901 W. State St. West Lafayette, IN 47907

© 2021 Purdue University | An equal access/equal opportunity university | Copyright Complaints | Maintained by Pest&Crop newsletter

If you have trouble accessing this page because of a disability, please contact Pest&Crop newsletter at luck@purdue.edu.