Curt Swift, Ph.D.
Grand Junction Free Press Gardening Columnist

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March 14, 2013
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SWIFT: Growing Cannabis: What you need to know about pesticide use

About 180,000 Colorado residents hold a valid medical marijuana registry card and 2,145 of those patients live in Mesa County. Many have designated a primary caregiver (someone who has significant responsibility for managing the care of a patient) which may involve the growing of marijuana as part of their responsibility.

Even though the medical use of Cannabis has been legal since Colorado's patient registry was established June 1, 2001, there are no pesticides labeled for use on this crop. In other words, you cannot legally treat these plants for the insect, mite and disease pests that infest medical marijuana.

Root aphid, powdery mildew, viruses and botrytis are problems I've noticed in the facilities I've worked with, and the lack of approved pesticides is a concern. Without legal-approved products, growers use whatever is available. Some of these products result in contamination, putting the patients' health at risk.

Growers in the know are using biopesticides, products that are relatively safe and should be labeled for use on Cannabis. These natural materials typically are very specific to the pest and are of minor consequence to the patient due to their short residue and low mammalian toxicity. Some biopesticides are even approved for organic use and would be the best products to use when legalized for use in the production of marijuana. Thankfully, there is an ongoing effort to register some pesticides for use on Cannabis in Colorado.

In addition to the concern about the illegal use of pesticides, growers also need to be aware of the Worker Protection Standard (WPS). Even if a pesticide is used illegally, WPS can still apply. Next time you pick up a bottle of a pesticide, check the label to see if it mentions WPS on the label. While this does not apply to homeowners, it does apply to agricultural employers. Growers who hire workers to assist in the production of Cannabis or any other crop are required to abide by WPS to ensure their workers receive information and training on how to avoid exposure to pesticides and pesticide residues. While these standards exempt immediate family members of the grower, i.e. spouse, siblings, parents, or children, if an uncle is hired to assist in the business, he must receive this training or the grower is in violation of this requirement. WPS is a way to protect the unsuspecting from contamination and the grower from a lawsuit.

Mycotrol O, an organic product containing Beauveria bassiana, is a great product for aphids. Beauveria bassiana is a soil-inhabiting fungus that feeds on insects. The Restricted Entry Interval is four hours during which time the grower, workers and others should not enter the treated area unless they are wearing the appropriate protective equipment. Even though Mycotrol O can be applied up to the day of harvest, the Worker Protective Standard requires anyone entering the treated area within 30 days of an application to have received training on decontamination, emergency assistance, emergency first aid, etc. There are 11 items required in the training. A record to keep track of everyone receiving the training is necessary. This requirement applies to caregivers who hire workers to help grow and process their products as well as every other agricultural producer.

To help keep agricultural growers legal, Jude Sirota and I will be conducting a workshop at the Country Inns on Horizon Drive May 9. This will provide the required WPS training. Pesticide applicator technicians are also required to receive training through programs like the one we are conducting. If you want to receive a brochure about this workshop or you would like a personal visit to your operation, give me a call at 970-778-7866 or drop me an email at

Dr. Curtis E. Swift is a retired horticulture agent with the CSU Extension. Reach him at or check out his blog at He owns Swift Horticultural Consulting and High Altitude Lavender.

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The Post Independent Updated Mar 14, 2013 01:14PM Published Mar 14, 2013 01:12PM Copyright 2013 The Post Independent. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.