Effects of Powdery Mildew on Cannabis Plants
Cannabis is the center of a multibillion-dollar industry, but it’s easy to forget that it’s also a plant. As legalization expands within a state-led framework that has no centralized standards, one of the biggest challenges for legal operators is figuring out how to grow people-pleasing cannabis stains profitably and at scale while also mitigating plant pathogens and pests that inevitably come with the commercial cultivation of an agricultural product. In this article, we’ll discuss one of the most frequently occurring fungal diseases faced by cannabis cultivators: powdery mildew.
What is powdery mildew?
Powdery mildew is a fungal disease that occurs frequently among all kinds of plants – including trees, vegetables, fruit, and other agronomic crops – and at every stage of growth. Commonly attributed to the pathogen Golovinomyces in cannabis plants and a variety of other fungi, infection is triggered by spores of powdery mildew on branches of mycelium known as conidiophores, each bearing asexual spores called conidia. When infected plants are disturbed, chains of conidia are released into the air then carried over long distances by the wind before landing on plant surfaces and beginning the germination process. Strands of the conidia spread and are uniquely able, unlike most fungi, to produce spores without moisture before ultimately penetrating leaves, flowers, and even trichomes.
While a plant can become infected with powdery mildew at any time during its life cycle, the infection thrives in warm environments and typically occurs during the mid-to-late summer months. Physical symptoms include patches of white powder that initially appear on upper leaf exteriors before spreading to lower surfaces, stems, and inflorescences (the complete flower head including petioles, bracts, stems, and flowers) usually within 14 days of infection. In addition to the visual signs of infection, lab tests can also confirm an occurrence of powdery mildew.
How powdery mildew affects cannabis plants
The fungi that cause powdery mildew are obligate parasites that rely upon a living host in order to survive. They also tend to be host-specific; this means that aside from a few exceptions, powdery mildew that infects one plant cannot infect another. But once a plant has been infected, its leaves experience a loss in cell function known as senescence, which can prematurely affect photosynthesis and yield. Though a white powdery appearance is common, the infection is characterized by a variety of symptoms that can include fungal lesions and spots ranging in color from yellow to green to black; leaf drop, curling, and discoloration; and the stunted growth of the plant and any emerging shoots. Powdery mildew spreads easily and though rarely fatal to its host, it can cause severe damage to individual plants and entire crops. According to one study on powdery mildew in legumes, outbreaks were found to reduce pea crops by up to half and soybean yields by as much as 60%. Such losses could be potentially devastating for any industry, but especially one as heavily taxed and scrutinized as cannabis.
The high humidity levels typical to indoor facilities make cannabis and hemp particularly susceptible to both golovinomyces and the podosphaeria macularis, the powdery mildew pathogen common to hops. When infected, a cannabis plant experiences much more than the telltale white spots visible on its leaf surfaces. The infection impacts photosynthesis to such a degree that it precipitates leaf yellowing and abnormal growth in cannabis plants, ultimately causing reduced yield. Powdery mildew can also destroy cannabis resin, leading to reduced potency. And all of these issues combined can result in impaired quality in the long run.
Yet as devastating as a powdery mildew infection can be, agricultural industries are no strangers to it. Adopting a proactive approach toward pest and pathogen management can help cannabis cultivators lessen the overall impact and, if caught early enough, even mitigate the potential damage. Not only that, but the variability of cannabis cultivars may result in different strains possessing varying levels of susceptibility to the fungal infection – presenting an opportunity for growers to seek out and cultivate genetics resistant to powdery mildew.
And it’s in producers’ best interest to be proactive when it comes to managing powdery mildew. Because ingesting or inhaling mold spores can cause a number of health issues ranging from lung and sinus irritation to severe allergic reactions or worse – particularly among people who have a weakened immune system – legal markets usually require such tests to ensure patients and consumers are not unwillingly exposed to this and other potentially harmful pathogens.
For commercial cultivators, having to deal with powdery mildew may be part of the job, but it doesn’t have to be burdensome. Taking cues from how other agricultural industries approach the issue, using them to create and implement standard operating procedures, and regularly implementing operational efficiencies into your facility can go a long way toward ensuring the optimal health of your plants – and ultimately, your business.
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- “Management of powdery mildew on hemp in the Pacific Northwest”. Oregon State University Extension, May 15, 2023: https://extension.oregonstate.edu/crop-production/hemp/management-powdery-mildew-hemp-pacific-northwest
- “Diseases of Cannabis in British Columbia.” Ministry of Agriculture, March 2021: https://www2.gov.bc.ca/assets/gov/farming-natural-resources-and-industry/agriculture-and-seafood/animal-and-crops/plant-health/diseases_of_cannabis_in_british_columbia.pdf