Painless prevention: Mold-reducing technologies can be a lifeline for growers

A variety of solutions that are safer than using harsh and often illegal fungicides

Bud rot. Powdery mildew. Gray mold. Botrytis. No matter what it’s called, mold- and mildew-related maladies can ruin a cannabis crop. The rise of legal marijuana and the increasing pesticide regulations governing the industry have revealed the widespread use of banned fungicides, such as Eagle20, resulting in numerous product recalls in Washington, Colorado and California.

But whether the root cause is steep fluctuations in humidity, weak genetics or contaminants in the air, cannabis producers can use a variety of technologies to reduce the potential for a mold breakout without resorting to dangerous chemicals.

An inside look at the WillowPure mold mitigation system, each of the 34 racks can hold up to 20 pounds on the standard unit. Shelves on the High Capacity unit can hold up to 40 pounds.


Unlike many other air sanitation solutions, the WillowPure is a turnkey mold-mitigation system designed as a final step for dried and cured flower. All it requires is a power outlet, a clean environment and somebody to run the equipment.

The machine produces pure ozone gas to kill a variety of fungi and bacteria. At the end of its cycle, the ozone is destructed back into breathable oxygen.

“One of ozone’s most positive characteristics is its natural ability to degrade back to oxygen,” WillowPure CEO Jill Ellsworth says. “For this reason, ozone technology, rather than irradiation, radio frequency, high heat or other solutions, has become popular in agriculture and in various food and plant applications.”

The machines come in two different models: The WillowPure Standard has two racks with 17 shelves apiece and holds about 20 pounds per run; the High Capacity unit features four racks with 17 shelves apiece and can hold up to 40 pounds.

The company tested the WillowPure for the past three years to ensure microbial degradation occurs without affecting the terpenes, potency color or structure of the harvested flower. The recommended run time is between two and 14 hours, but the company’s own testing has shown a 50% reduction of coliform-forming units when running the machine for as little as one hour.

“Of the product we have serviced on-site in the Colorado market which has previously failed testing, passing rates have reached as high as 90% after one run through the WillowPure system,” Ellsworth says. “Given the variability in facility air quality and other potential contamination hazards, this is a significant indicator of our system’s success.”

Once plugged in, the AiroClean420 can remove several threats to plant health almost immediately.


With more than 1,000 systems sold to growers in North America, the AiroClean420 is one of the most popular air sanitation solutions in the cannabis industry.

The system does not produce or generate ozone, hydro-peroxides, multi-cluster ionization or any other type of emissions, making it safe for operators and the environment. The sanitation occurs within the unit’s reactor bed. One AIRO-50 unit can typically sanitize 10,000 cubic feet of space, while drawing only 2 amps with power consumption of 180 watts.

A fan draws air through the AiroClean420’s reaction chamber where high-intensity PCO lamps form millions of hydroxyl radicals that mineralize imperfections such as pollen, viruses, bacteria, mold and fungi into trace amounts of CO2 and H2O before it exits through the rear of the unit as clean air.

The AiroClean420 was originally engineered for use within a closed-loop indoor cultivation facility, but later this year, the company will introduce a new model that is more appropriate for greenhouse environments, where temperature management and air circulation require rapid outside air exchange.

For more than 20 years, the same core technology has been serving the global food and beverage industries to help maintain air purity. The company’s air sanitation technology, which is listed as a Class II medical device by the U.S. Food and Drug Administration, was introduced into the marijuana industry to minimize the risk of fungal disease contamination.

“If the objective is to add another layer of protection or prevention from airborne powdery mildew or other fungal disease contamination, then we believe AiroClean420 is the very best solution available today,” says President and CEO John J. Hayman III. “Within a recirculating, closed-loop grow facility, if set to specifications based on environmental conditions and desired placement locations are followed, center of the room and in direct proximity with airflow, we do not see any downside whatsoever with our AiroClean420 system.”

One of the the Sanuvox Biowall Max’s high-intensity germicidal UVC lamps.


The Sanuvox Biowall Max system uses high-intensity germicidal UVC lamps mounted on anodized aluminum parabolic reflectors designed to create 360-degree radiation. The company claims its patented UVC chamber kills up to 99.9% of airborne bio-contaminants. The system is designed to be integrated directly into the cultivation facility’s HVAC system, parallel to the airstream.

The Sanuvox system was designed for indoor cannabis growers, but it can also be used in greenhouses to fight botrytis and other common fungi parasites.

A single Biowall Max-60 unit can sanitize a 10,000-square-foot greenhouse, assuming a roof height of 10 feet and a ventilation system that provides six air changes per hour, without any residue or toxins. It does not produce ozone, hydroxyl radicals, super oxides, ions or other toxic oxidizers that can harm the cannabis plants or create an unsafe environment for workers.

“The Sanuvox system will disinfect powdery mildew by up to 99.9% within every hour of operation,” says founder and vice president of engineering Normand Brais. “It is a completely green cleaning method with zero residue, and it is non-toxic, unlike pesticides or fungicides.”

Sterile-Aire’s UVC bulbs kill up to 97% of the mold circulated through cultivation sites.


Inside an air-conditioning system, mold can grow on the coils and in the dark, damp spaces between the fins. The viscosity of the mold growth makes it stick to the metal fins, much like a barnacle on the side of a ship, says Jeff Scheir, Steril-Aire marketing and product development manager. Not only does this biofilm reduce the efficiency of the system and shorten its lifespan, but it also creates a breeding ground that enhances the molds in the air.

Steril-Aire systems are designed to attack microbial growth directly at its source, using the anti-microbial properties of the C-band of ultraviolet light to kill 50% to 97% of the mold in the air. The company installs powerful UVC lights next to the cooling coil that renders the organic material non-viable.

“Now when the air is brought through the air-conditioning system, it comes out cleaner than when it went in,” Schier says.

In addition to killing microbial growth at its source, rather than “on fly-by” in the ductwork, what really sets Steril-Aire apart from its competitors is the intensity of the UVC bulbs, Schier says.

The company’s big breakthrough in the 1990s was creating a bulb that was about eight times more powerful than its competitors, Schier says. While that gap has closed in the past two-plus decades, Steril-Aire’s bulbs are still about four times more powerful, according to the company. The bulbs typically need to be replaced about once a year.

With a Steril-Aire system, the lights are sized appropriately for the facility’s air conditioning. Even when the room is not being heated or cooled, it’s important to keep the fan on to continue sanitizing the air. The Steril-Aire units come in many different shapes and sizes and can be retrofitted to almost any air-conditioning system.

Steril-Aire’s UVC bulbs do not produce ozone, but some manufacturers do. Growers should take precautions against exposure to UVC light, which can be a skin and eye irritant. Looking directly at UVC light will result in a flash burn, similar to what welders experience, although the irritation typically lasts less than 72 hours.

The company also makes a stand-alone air purifier called the Steril-Zone for grow facilities that do not have central air. Its industrial-grade, variable speed fan is capable of moving air at 250 cubic feet per minute. One Steril-Zone unit can handle about 1,000 feet of grow space, and users have also had success installing them in drying rooms.

“Everything that we do is designed around understanding the bugs and being able to attack the bugs faster than they can grow,” Schier says. “If you’re killing it slower than it’s growing, you might slow down its progression, but you’re not solving the problem.”


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