UVA UVB Lighting To Kill Powdery Mildew And Mold

I have been doing some research into the use of UVA UVB lighting to either control, kill or eliminate powdery mildew and mold on medical marijuana cannabis plants.

I recently along with just about everyone else have been struggling with powdery mildew this past year.

Powdery Mildew Myth Debunked

I would first like to dispel some of the myths that are associated with powdery mildew.
Many people believe that powdery mildew is caused by too much humidity or that temperature issues can cause it. This is not true. Powdery mildew is caused by poor air quality control and is usually contracted through another plant that was introduced into your room or from the outside air coming into your room. It is critical that your outside air is filtered and not allowed to just free flow into your room. If you are growing in organic soil it is always possible to contract any number of pests, diseases or viruses. Many of them are present at all times on our plants and in our grow media. Just like the human body many diseases and viruses exist in our body but never become a full blown outbreak. Given the right environment the virus will accelerate. With poor air quality control you are providing the environment powdery mildew needs to explode. Once it starts it is nearly impossible to eliminate.

Excellent air quality means that you have the correct humidity, optimal temperature, excellent airflow, air movement and good air exchange. If you run a closed room you will need to supplement with CO2. Fans need to be located above and below your plants to eliminate stagnant air and provide the plant with CO2 that it needs. The slight flutter of the leaves allow the marijuana plant to uptake CO2.

How to Control The Spread Of Powdery Mildew

I have found that if you isolate the cannabis plant and treat it regularly it is possible to finish the plant or plants off and lower the chance of exposure to the rest of your crop. The mold thrives in darkness and the lower branches of your plants. It is critical to lollipop or strip off as much of the lower branching as possible followed by thinning the plant out either by deleafing the larger fan leaves or at the very least remove as many of the infected leaves as possible. If your plants are touching they will transfer the powdery mildew or mold at a much faster rate. I usually deleaf my plants in week 3 or 4 anyways with no adverse effects whatsoever. This allows more light to reach the lower branches and increases bud size. I will write up a separate blog about deleafing at a later date. I use a mix of products to control and eliminate the powdery mold but it is not a sure thing. I mix up a 5 gal bucket of Mighty Wash. I add in 80 ml of SM90 which can also be used as a root drench by itself to control and eliminate the mold or mildew. In addition I add in 40-80 ml of Neem oil, 32 oz of peroxide, 40 ml of Organocide and I have a petroleum base product I add 40 ml of that as well. I also add Coco Wet. Each of these products are comprised of different ingredients and serve a different purpose in the control or elimination of pests and disease. I have never had any one of my 22 strains show any adverse effects from this mix. I also spray with my lights on so I can get every nook and cranny of my plants top and bottom of the leaves and stalks. Another option would be to fog it in with a fogger which uses a lot less product and does a better job with coverage. Make sure you where a mask so as not to taste this in your mouth for next couple of days. All products are organic and will not hurt you or your plants. I have even sprayed all the way up to my 7th week in bloom and had no issues. My only concern was taste. I couldn't taste anything maybe just a little more harsh than normal at most. If desired you can also add in your foliar sprays such as Liquid Light, Sea Green or Magic Green at the same time.

During my fight to save my crop all my strains and mother plants I have researched many methods of control or elimination. What I have found is early treatment can control it or maybe eliminate it. Once the plant has become covered in powdery mildew it gets into the root system and becomes systematic. Once the powdery mildew becomes systematic it is nearly impossible to eliminate.

UVA UVB Lighting Research To Eliminate Powdery Mildew On Vegetable Crops

My research led me to some studies that had been done on lettuce plants cucumbers and tomatoes. The research had found that with a minimum exposure of 15 min per day from the UVA UVB lighting the powdery mildew was in some cases controlled and other cases eliminated. I found this to be very interesting because for the past 3 years I had been using my UVA UVB lighting to increase THC up to 5% UVB UVA Study Results Increses Marijuana Cannabis Potency By 3-5% and never had any powdery mildew issues during that entire time. When I moved my room to a new location I discontinued use of the lighting and within 3 months started having issues with powdery mildew. I never made the connection.

This makes complete sense because many companies sell uva uvb filters for fish tanks and ponds that filter out and kill algae and other unwanted micro organisms. They also purify and clean the water of unwanted bacteria.

Test Results In My Grow Room With The Ultraviolet Lighting

I have since then installed the new T5 HO 54w Reptisun 4ft bulbs in my room which are 2x more powerful than the T8 Reptisun bulbs I used last time. Link to Reptisun 10.0 UVA UVB T5 HO 4FT bulbs I will be doing some further testing with these bulbs as compared to the T8's I was using before to increase the cannabis potency. Stay tuned for the results!

I run my UVA UVB bulbs during the full 12 hr bloom cycle. Since installing the bulbs I have had no further progression of the Powdery mildew and it seems to have killed off all remaining mold spores on my plants. It has been 2 weeks since I installed them over the plants. If your plants are really tall you may have to position the UVA UVB lighting near the bottom of the plants so it penetrates down into the canopy or near the underside of the plant where the majority of the mold will grow.

My plants that are in the vegetative stage have been mostly cleaned of the powdery mildew but every now and then I would get a few spots here and there. I placed my veg plants under the same lighting and have not had any signs of mildew since.

Due to the fact that powdery mildew is a viral infection and can not be killed off without damaging or killing the plant I am waiting to see if my new clones develop any new mold spores. If not that means the powdery mildew is wiped out of the plant completely. This would be a revolutionary finding because many growers have lost entire marijuana crops due to powdery mildew. There is no product on the market that can eliminate it in bloom. Some claim to eliminate it in vedge but this has not been proven to be effective 100% of the time.

How to Dry medical marijuana with powdery mildew

In addition I have found even if you can control the mold or mildew once you cut the plant down and start the drying process the powdery mildew explodes all over the buds and the rest of the plant that was not previously contaminated. I found that if I dry with a light on or a set of lights on in my drying room the powdery mildew does not continue to grow. I have had no adverse effects from drying with my lights on contrary to popular belief that you must dry in the dark. So there goes another myth busted!

The mold only grows in humidity above 10-15% however if we kept our rooms at this level we would have some serious issues to deal with. Plants will not root, they grow very slow, buds do not swell and when drying the finished medical marijuana would be dust! So even though humidity does play some role it is not a path we can travel down.

Further Testing Needed With UVA UVB Lighting

I would like to see more testing done on other forms of mold and mildew such as bud rot mold, grey mold, blight, downy mildew etc. I am confident the the UVA UVB lighting would eliminate all of these as well.

In closing it seems that we as growers need to plan on adding UVA UVB lighting to their rooms. It has been proven to have many positive effects on the marijuana plant when grown indoors. After all in nature all plants need this light spectrum. This spectrum triggers growth responses and protects the plants from immune deficiencies as well as unwanted pathogens.


Links to related blogs:

How To Grow Marijuana Like A Pro

UVA UVB Lighting To Kill Powdery Mildew

UVB UVA Study Results Increses Marijuana Cannabis Potency By 3-5%