Powdery mildew (PM) is a fungi in the order Erysiphales, with Podosphaera xanthii being the most common species. It is common worldwide and tends to prefer environments with high humidity and moderate temperatures. Greenhouse and indoor growing tents provide ideal environments for growth, which is why it is a common problem for cannabis cultivation in particular. PM can quickly spread to the entire plant and render the plant unusable, as PM is toxic and can not be safely consumed by the end user. Medical marijuana is tested by law in many states where it is legal, and plants that have any detectable amount are not legally sold to the customer.
There are a number of chemical that are available to treat outbreaks, but most are not organic, or are simply too toxic to use on a plant that is bound for consumption. Ultraviolet is both organic and safe, plus it is easy used as a preventative so PM never starts. This is why it is rapidly replacing chemicals.
The key to suppressing all molds and mildews is using a wide band UV source of high intensity. This is where the Flower Power comes in. Because it is a 34%UVB/66%UVA bulb with no visible phosphors, it produces the entire UVA/UVB spectrum with a graduated intensity. This means it is lower in the UVB region where each photon has a lot more energy, and higher in the upper UVA bands where the energy per photon is lower. This give the Flower Power a flatter energy curve, which makes it extraordinary suited for the prevention of these fungi.
Of course, the first step to preventing PM is good methods, sterilization of the environment and humidity control. You can run the Flower Power for 24-48 hours continuously in an empty and freshly cleaned grow tent or room to provide extra sterilization. This is quite common. Then you use the lamps for 2 to 4 hours a day (depending on strain and distance to plant) beginning just before you go into flowering. Use an hour a day for a week, then two. You can monitor the plant response to the UV (it takes at least 3 days for the plant to react if you give too much) and adjust as needed.
Generally speaking, you want to use two Flower Power bulbs per 1000w hood. This is mainly about coverage, as the lamps are extremely strong. a 4x4 tent might use just one, but you may need to move it periodically to get proper coverage.
We have a number of customers that use Flower Power solely for preventing powdery mildew and it is proven to work, even in hostile environments. However, there are other benefits you will get when using them properly. Insects can't stay in an ultraviolet environment, particularly soft skinned insects like mites. It messes up their DNA, so it is a good addition to your good methods in killing and/or reducing the likelihood of an infestation.
The most obvious benefit is higher THC production. Our customers are consistently getting over 30% total THC when used properly. Using cloned plants as a control, we have seen anywhere from 15% to over 30% increase in the total THC. 22% goes to 30%, etc. It also appears to increase terpene production and other oils within the plant. It doesn't seem to affect CBD or CGN production at all. (note: running the bulbs in pulse mode, 15 on, 45 off, 6 hours a day does increase CBD). So yes, they have three main benefits: Kills mold, kills insects, boosts THC and terpenes.
How it boosts THC is pretty straight forward. Unlike all other UV lamps, we can produce significant output from 280-290nm. This is where the UVR8 protein (common to most plants) gets triggered, and it sends a chemical message to the plant to protect itself. In the case of cannabis, it produces more THC as THC has a very high affinity to absorb UV.
I get asked this a lot, so I wanted to address it here. UVC bulbs (typically centered around 256nm) are used for water purification and air purification all over the US. It is certainly effective at killing pathogens and all living things. That is the problem: your plants are living things, and so are you.
The earth's atmosphere filters out virtually 100% of the UVC that hits the atmosphere, so none hits the ground. This means that no living animal, plant or fungi has any built in immunity to it. They didn't have to evolve with UVC, so it is completely foreign. This is one reason why it is great for certain applications, where you can prevent the light from irradiating anything you care about, so it can completely destroy everything you want gone. But it is a terrible choice for plants.
UVC doesn't penetrate as deep as UVB, which itself doesn't penetrate as well as UVA. What it lakes in penetration, it more than makes up for in energy per photon. A run of the mill high pressure UVC bulb will give you a flash burn with just a few seconds of exposure. We have a few customers who have tried it with their plants and destroyed entire crops. Simply put, it fries the plant at the surface, rendering it unable to breath. More than a few seconds of exposure to a human will result in a trip to the emergency room as well. Even the low power "wands" are not a good way to go. First, they don't increase THC, you don't trigger the UVR8 protein, you can't run them long enough to kill insects (where the UVA really shines since it penetrates their skin) and it is very risky for the user as well. Just don't.