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Biorational Fungicides For Indoor Applications

October 23, 2020

  • What Are Biorational Fungicides?
  • OMRI Listed
  • Table of Biorational Fungicides

What Are Biorational Fungicides?

Biorational fungicides is an unofficial definition for fungal control materials that are relatively non-toxic to the ecosystem. This is generally why a lot of biorational fungicides qualify for use in organic greenhouses and organic indoor cultivation facilities. There are several categories of biorational fungicides and they include microbials, botanicals, minerals, and synthetic materials that have several different modes of action or function. Most biorationals function similar to conventional chemical fungicides in that they directly affect the target pathogen by preventing spore germination or reducing spore production and growth. They can be formulated as liquid solutions, wettable powders, or emulsifiable concentrates. Biorationals typically have the greatest efficacy when used preventively, but can still be effective to remedy diseases caused by pathogens.

OMRI Listed

There are lots of biorationals that are approved for use on crops that are certified organic. Products that are approved for organic production are designated with “OMRI” or “OMRI listed” labels which indicate they are approved and listed by the Organic Materials Review Institute. OMRI was founded in 1997 as a nonprofit organization that provides organic growers, manufacturers, and suppliers an independent body to review products intended for use in certified organic production. Despite products being OMRI listed, it is important that cannabis growers consult their state department of agriculture for pesticides approved for use in commercial or residential cannabis production. Lists of approved pesticides can generally be found on the department of agriculture websites. The Colorado Department of Agriculture (CDOA) updates their approved pesticide lists periodically and can be found readily available on their website.

OMRI Listed Label

OMRI Listed label found on certain biorational fungicides.

Citric acid is a very popular active ingredient in biorational fungicides that is found in vegetables, fruits, and plants, and it is generally recognized as safe. Biorationals containing citric acid have been registered with the United States Department of Agriculture (USDA) since the 1970’s. Citric acid is commonly used to target powdery mildew which is a mildew that commonly afflicts cannabis plants. Examples of other common active ingredients found in biorational fungicides include sulfur, bacillus subtilis, rosemary oil, and soybean oil. When applying biorational fungicides to cannabis plants it is important to spray frequently throughout the plant’s life as a preventative measure and when spraying the coverage should be thorough for the greatest efficacy. Spray coverage should be as thorough as a car paint job on both the topsides and undersides of the plants.

Table of Biorational Fungicides

Active Ingredient
Citric Acid Cinnamon Oil
Sulfur Thyme Oil
Bacillus Subtilis Clove Oil
Rosemary Oil Harpin Protein
Soybean Oil Reynoutria Sachalinensis Extract
Neem Oil Insecticidal Soap


  1. Brian P. Baker and Jennifer A. Grant. (n.d.). “Citric Acid Profile - Active Ingredient Eligible for Minimum Risk Pesticide Use”. New York State Program Integrated Pest Management, Cornell Cooperative Extension. Cornell University.

  2. Wade H. Elmer. (2008). “Biological biorational fungicides offer control options”. NMPRO - Nursery Management & Production.

  3. (n.d.). “Biorational Disease Control”. University of Massachusetts Amherst, The Center for Agriculture, Food and the Environment.

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