What is powdery mildew and why should you prevent it?


Powdery mildew is a fungal disease affecting a wide range of plants. It typically appears first on plant leaves but can spread to all parts if left unchallenged. It is one of the most common diseases for nursery plants such as flowers, vegetables, woody plants and cannabis. Species of powdery mildew are specialized to infect only plants in one genus or one family. This means infection will not spread to other species of plants in other plant families. For example, one species of powdery mildew infects Calibrachoa, Verbena, petunia and cucurbits. This means growing squash and cucumber in the same greenhouse as the aforementioned flower species since cross contamination can occur in an outbreak.





Powdery Mildew and Cannabis


Powdery mildew has garnered a lot of attention in the industrial hemp and cannabis industry. For the purposes of this discussion, we will simply label both industrial hemp and cannabis as ‘cannabis’. Industrial hemp and cannabis are essentially the same plant in the Cannabis genus with hemp being defined as less than 0.3% THC and cannabis defined as greater than 0.3% THC. The species of powdery mildew that infect the cannabis family of plants are different organisms that those that affect other common indoor crops, such as tomatoes, cucumbers or lettuce. What isn’t known is how many different species there are that affect cannabis. A 2017 study genetically sequenced infected cannabis plants from the U.S. and Canada. It found that the DNA did not match any known powdery mildew sequences to date. Needless to say, there is still much to learn about powdery mildew, especially in the cannabis industry.

Powdery mildew is problematic not only because it can weaken the productivity of a cannabis plant, but if it spreads to the buds, they cannot be sold. With the unique consumption methods of cannabis, consumer safety is a huge concern. Some people believe contaminated buds can be salvaged for use in concentrates, such as live resin or CO2 oil. But there is not a clear consensus regarding the safety of these products when derived from infected buds. Ethanol extraction and CO2 are currently thought to be the best way to rid extraction products of powdery mildew. More testing is needed to confirm this and consumers are advised to look for dispensaries that list product testing results.

Powdery mildew can become active at any time given the right environment, including harvest or the drying process. Cannabis is generally dried and cured slowly to bring out the best qualities of the bud. This means the plants will spend a good deal of time open to potential contamination. Cannabis is generally best dried slowly at lower temperatures. During the first 72 hours, water loss from the plants is rapid, increasing humidity in the air. Keeping the area clean is imperative, as many spores germinate in moist environments with temperature ranges between 50-70 degrees Fahrenheit. Controlling temperature, humidity and airflow during drying and curing is just as important as it is during the different stages of growing cannabis.

Industrial hemp crops are treated differently than the previously mentioned cannabis depending on the end use. Most hemp crops destined for CBD extraction are rapidly dried in hours rather than days or weeks. In this drying process, heat and lots of airflow are introduced. Contamination and detectable levels of powdery mildew spores aren’t usually an immediate problem at this stage due to low humidity and dilution of spores. However, problems usually arise during the long term storage of the dried hemp while waiting for processing. At this stage moisture intrusion and absorption can contribute to the growth of the previously spread spores. Most harvests occur around October and depending on processor availability, could sit through the damp winters and subsequent warming spring seasons which create ripe conditions for crop loss.

Strategic solutions for short or long term storage of industrial hemp are to ensure storage rooms are properly sealed from outdoor environments, provide chemical- or refrigerant-based dehumidification and provide active air filtration and circulation.

With an eye towards compliance of both domestic and international Good Manufacturing Practice (GMP), the integrity of the harvest and subsequent storage are cornerstones that ensure a safe transfer of product to the processor or downstream integration into the food chain. It is the responsibility of growers, processors and integrators to ensure the quality of both raw and finished product and to follow ISO 9000/9001 quality manufacturing procedures for acceptance into both domestic and international markets.

Indoor Growing Environments






Clean Air to Combat Powdery Mildew



The design of the Element Grow E1 Air Filtration and E2 Air Filtration with E-Guardian Monitoring units are based on proven scientific research maintained by the American Society of Heating Refrigeration and Air Conditioning Engineers (ASHRAE) and backed by field proven testing. The 2018 ASHRAE Position Document on Filtration and Air Cleaning evaluated the most current forms of air filtration or air cleaning devices and summarized that, “Filtration technologies, in which particles are removed by attaching them to the media (often called mechanical or media filters), have been documented to be capable in many cases of reducing particle concentrations substantially, including reductions from levels being above to levels being below the associated regulatory exposure limits for reducing health risk set by recognized cognizant authorities.” The E1 and E2 are 2,000 CFM hygienic fan filter units in an energy efficient package proven to knock down contaminant levels (0.3 microns and larger) by 98% within 30 minutes of runtime in a 2,000 sq. ft. or 20,000 cu. ft. space. The E2 can monitor contaminant levels and automatically react when levels go up, increasing its fan speed to capture more contaminants in a shorter amount of time. Energy efficient, non-pollutant emitting, and easily cleaned and sanitized inside and out, these units were designed for prevention and with Good Manufacturing Practices regulations in mind.The E2 is an excellent strategic step to help immediately create required GMP facility clean environment needs and fulfill monitoring compliance requirements outlined by the regulations.

Contact us for more information about taking preventative steps against powdery mildew and maintaining clean air environments for your plants!

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