OVERVIEW
Powdery mildew is a common, easily recognized, and widely spread plant disease. Whether you are growing veggies, cannabis, or your favorite ornamental, powdery mildew can be disastrous if left unchecked. This disease is often a cosmetic concern since it typically results in disfigured and unsightly plants rather than plant death. In other cases, such as powdery mildew of tomato or powdery mildew of cannabis, infections can significantly reduce fruit production and may also result in plant death. For cannabis, powdery mildew is one of the most destructive infections. On a small scale, it can cause an entire seemingly perfect crop to fail regulatory testing, resulting in huge losses. On a much larger scale, powdery mildew can devour cannabis flowers to a catastrophic level of destruction, plaguing growers to no end.
Powdery mildew tends to be more problematic outdoors in mid to late summer when day-night temperatures favor high relative humidity (RH). Interestingly, powdery mildew does not require water on the leaf surface for infection, which may increase the odds of an outbreak. The severity of the disease depends on several aspects, including the host plant, plant health, and environmental conditions. Do not be fooled; powdery mildew can develop anytime during the growing season. For indoor growers, powdery mildew is a year-round battle, especially since we create our micro-climate. Depending on the level of control over your environment, this can be good or bad. Indoor and outdoor cultivators must be vigilant to avoid widespread cases. Because powdery mildew thrives in dry conditions with high relative humidity, environmental balance is invariably critical. Regular inspections and preventative procedures can drastically help to mitigate infections.
PREVENTION AND TREATMENT
Powdery mildew is easily identifiable in terms of its greyish-white dusty powder-like characteristics. As a host-specific fungus, there are many types of powdery mildew, though all types generally display symptoms the same. Typically, by the time you see the problem, the powdery mildew infection is already further along than you want. Ideally, preventative measures and good growing practices are your best approach to mitigate and control this disease. Routine applications of lactic acid bacteria can help to prevent a powdery mildew outbreak. To further stay on top of things, regularly inspecting your garden with a UV light can significantly simplify the task. That is because powdery mildew conidia (spores) are autofluorescent and will glow under ultra-violet light. Adding a UV light can level up your inspection procedure and save you time and stress. And quite possibly your crop.
Hydrogen peroxide, an often-used method for controlling powdery mildew, only causes the hyphae to collapse, allowing the spores to remain and spread infection. And in many cases, hydrogen peroxide accelerates the germination process of these spores. In contrast, lactic acid bacteria kill both the hyphae and eliminate spores. Used in the proper method, you could consider these two the one-two punch for natural powdery mildew control. We like to culture our LAB and utilize it in our garden SOP as a preventative measure against powdery mildew. Plus, it works great as a compost accelerator. Generally, we recommend using LAB diluted with clean water at a 1:1000 ratio. With a severe case of powdery mildew, it is best to use a 1:1 ratio or pure lactic acid bacteria serum if possible. Add your LAB to a sprayer and apply as needed.
REFERENCES:
Oliveira, Pedro M et al. “Cereal fungal infection, mycotoxins, and lactic acid bacteria mediated bioprotection: from crop farming to cereal products.” Food microbiology vol. 37 (2014): 78-95. https://doi.org/10.1016/j.fm.2013.06.003
Twamley, Tony et al. “A Microbial Fermentation Mixture Primes for Resistance Against Powdery Mildew in Wheat.” Frontiers in plant science vol. 10 1241. 9 Oct. 2019, https://doi.org/10.3389/fpls.2019.01241
Xu, Xinze et al. “Characterization of conidial autofluorescence in powdery mildew.” Heliyon vol. 8,12 e12084. 5 Dec. 2022, https://doi.org/10.1016/j.heliyon.2022.e12084
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