Did you know that the pathogen, powdery mildew, lives in the bits and pieces of plant debris leftover from your previous growth, and therefore, live on in your soil?
Did you know that the powdery mildew that attacks your zucchini is not the same powdery mildew that attacks your tomatoes, or my cannabis?
If you have moderately warm growing seasons, but still deal with humidity, you have probably seen powdery mildew in your garden. High humidity, and moderate temperatures (60-80 degrees fahrenheit) are when the pathogen flourishes. In some cases, it is more of a cosmetic issue than a real danger to your plants, but in other cases, powdery mildew leads to an unhealthy plant that you do not want to ingest in your body. The pathogen primarily attaches itself to leaves, but if you find it in developing flowers, they must be removed.
There are many homemade remedies for powdery mildew application. I have no personal experience with any of them. The methods I use to fight powdery mildew are as follows:
1) The first method, of course, is prevention. To that end, we do practice the process of solarization, as previously described in the Bed Setup blog. The heat will kill any pathogens left in the soil.
2) Once you are growing, the greatest prevention against powdery mildew is aggressive pruning and plant maintenance. Cannabis needs air flow. Branches and leaves crammed together are a recipe for disaster. There must be a way inside for air to proceed freely and keep the plant dry. Moisture from humidity is guaranteed to bring pathogens.
3) Even with proper ventilation, if humidity is high and does not go down during the day, pathogens will form. At that point, the only way to fight is via foliar spray. For this, I primarily use one fungicide, with another spray as backup. I use a product called Regalia, which is an extract from the giant knotweed plant (Reynoutria sachalinensis). When it is sprayed on cannabis, it activates the natural defenses of the plant. It is ideally meant as a preventative spray. Once sprayed, it takes one to two days before the plant resistance takes hold. It is not a systemic fix, however, and will have to be reapplied to catch all new growth. It is recommended to apply every one or two weeks.
4) I will also use Neem oil for powdery mildew in two applications. One is when I’ve sprayed the crop with BT for worms, and I can’t spray Regalia for a week. I’ll use Neem during the interim. I’ll also occasionally use Neem if there is a severe outbreak and I need to hit it with something different. I will use it as a spot spray for specific trouble spots.
I began using Regalia during my second year. I could see it was effective. But during certain conditions, like when we get a period of high humidity that does not go down during the day, the situation calls for more aggressive treatment. During the third year of growing, I told Brenden I had an idea about how to treat powdery mildew: I was going to out-work it.
Beginning in the middle of the 2018 grow, and proceeding through all of last year, I made a commitment: Once my cannabis plants have had a full month of growing in the beds, and before we get our typical, sustained humidity of August, I will spray Regalia every other day. The directions say to repeat spraying every 1-2 weeks, and up to that key point on the calendar, I’d been spraying once a week. I found that when conditions became acutely bad, that was not enough spraying. By increasing it to every other day, I’m not giving the pathogen a chance. I want to maintain the highest level of immunity possible. The only residual impact I’ve witnessed by this sustained increase is a darkening of the base stalk from accumulated drenchings. It washes off. During the worst, we will still see a few leaves turning white, that somehow escaped the soakings.
However, by using this protocol, we probably decreased our incidents of powdery mildew by over 90%. The main places Brenden found powdery mildew last year were from parts of the plant well over my head. I had a hernia last year while we grew, and I could not climb up and effectively reach some of the spots with my hose when the plants became large. In fact, most of the powdery mildew we get now is not an issue for the healthy production of flowers.
Some more good news: Regalia treats all forms of powdery mildew. If you start early, and spray once a week, you won’t see any powdery mildew on vegetables or fruit. If you’ve had this pathogen on your plants in the past, it’s somewhat miraculous for it to not appear.
If you have a smaller crop, just a few plants, you can probably get by with a homemade solution. But if you have a crop of many plants, you will need a better tool.
Important application notes: Like Neem, you do not want to spray Regalia in direct sunlight. You can spray during the day, if it is cloudy or overcast, but you must be very careful. Direct sunlight literally changes cellular structure (the stoma closes). This is what causes the burn. I’ve had days I was certain the sky would never clear, only to have the sun break through the fog WHILE I’M SPRAYING.
These are the moments I’m grateful cameras don’t record my every move. I have had to stand, more or less in place, arms spread like some bald, behemoth bird, for 30 minutes, while the sprayed plant dries, keeping my body over that plant and protected from the sun. This is not possible when the plant is over your head. I do keep tarps, and plant cloth to drape over plants, for this reason.
After a fiasco like that, the choice to get up before the sun and spray is easier.
But last year, I finally added a component that is a true game changer when it comes to foliar sprays. I purchased a 4 gallon, battery powered foliar sprayer.
Oh my goodness, what a difference. When my plants get large, it will take about six gallons every time I spray. That means emptying the four gallon tank and re-filling one time.
Prior to purchasing this foliar sprayer, I was using a one gallon manual pump sprayer. At their peak, every foliar spray was taking me two to three hours. I’d prime the pump, spray, prime the pump, spray, prime the pump, spray, etc., refill the bottle and repeat. To do this before the sun hit our plants in the morning, I needed to begin spraying no later than 5:00 a.m.
Now, with the new sprayer, the entire process takes no more than 40 minutes. Most of the season, sprays will be 30 minutes or less.
Neem takes the longest, because you have to make certain you spray both sides of every leaf and flower.
On the other hand, I only recently discovered that spraying Regalia has a transliminar effect. If you spray the top of a leaf with Regalia, it will transfer the immunities to the other side. Knowing this will further aid my time management, and allow for quicker sprays during the day when a convenient and cloudy opportunity arises.
One more key component to spraying Regalia is to spray the soil. Pathogens live in the soil. So if you can build up immunities at the soil level, you are not as likely to see the pathogen on your plant. This is especially true after solarization.
For me, Regalia is one of my necessary expenses. Like so many other things, it is not cheap. I generally go through two large bottles a year, and that costs me about $250.
Ok, so we’ve dealt with powdery mildew. Now, we’re ready for the biggest challenge we face every year, during the entire flowering cycle: Mold.
Supposedly, Regalia helps build up immunity to mold, but I have seen far less visual evidence of this than I have for powdery mildew prevention.
There is nothing as sickening, as a grower, than finding mold on a flower. If you grow in a coastal climate, you will face mold every year. You cannot completely avoid it. The goal is to prevent as much as you can, and remove what you cannot prevent.
Mold prevention is a season-long process of mindfulness, though the time when it is most prevalent is during the flowering phase. We begin however, as soon as we start to prune the plants. Pruning should probably be a category for blogging, but I’ll be referring to it so often, it will be explained in process. Aside from foliar sprays, pruning is the single most effective tool in your pathogen prevention kit. Cannabis ideally should remain dry, so there needs to be space between each stalk. This is not as critical during vegetative growth as it is during flowering. That’s another reason for the pre-dawn spray. Plants will have all day to dry out before overnight humidity makes them drip again.
Another subtle, though extremely important key, is to be mindful the entire growing season of how you prune in general and cut things off in particular. Accidents routinely happen to plants. Be it a careless cut, or a branch being broken by an errant pass of the foliar spray hose, there will be damage to some of the plants you grow. When you cut anything, you are opening the door to pathogens.
So, two of the tools we keep at the ready in the garden are organic honey and rubbing alcohol. When we prune, and we cut close to the stalk of the tree, it is wise to apply a coating of honey to the injury. It is a sealant, and helps prevent pathogens from an easy way inside the plant. We probably use two squeezable jars of honey per season. Rubbing alcohol is for when mold is seen. When you cut a flower, or branch, with mold, you must make certain you cut beyond where the mold is found and treat that cut carefully with alcohol. Alcohol will damage flowers, so cotton balls, a Q-tip, or even a dab on a gloved finger is advised in application. (Then change your gloves) Alcohol kills mold. It won’t stop it from spreading if the conditions that cause it are pervasive, but it will kill what it touches. It’s a good year when we don’t use much rubbing alcohol. Last year, we hardly used any.
But that hasn’t been the case all years. In particular, the second year was brutal. That was the year I tried not using BT. Worm and caterpillar scat caused us to lose about 30% of our crop. Almost all of our problems could have been prevented with proactive BT sprays.
In truth, however, nothing could have prevented what happened to our ill-fated Granddaddy Purple. The year we grew this famous cultivar, my second year of growing, was Brenden’s first year of helping me. I had 18 plants and I was honestly overmatched. Brenden’s introduction to growing cannabis was under a full scale fire alarm of pathogen issues. And the Granddaddy Purple was at the heart of the problem.
She was a clone. That was the last year I grew from clones. They are nice, but they are not as resistant to disease as plants with tap roots. Beyond that, however, this particular cultivar should only be grown inside. Growing it outside, in a moderate coastal climate, is a complete failure of planning on the part of the grower (me). GDP grows in a tangled maze. It produces some of the most legendary looking kolas of all time, but it grows crammed together like canned fish.
Brenden and I recognized early in the flowering process that we were in trouble on this plant. I made an executive decision. This would be our mold training plant. If we ever had a plant like her again, we would toss her immediately, but this one year, we used this plant as our learning plant for how to salvage, if we must. The goal was to save as much of her as we could, treating every problem along the way. I can say it was a brutal process, and the only fun came from our dark senses of humor. We will never grow a plant like GDP again. We pruned and treated that plant all the way down to the final product, which yielded a mere 96 grams. Btw, what we eventually harvested (ten full days before projected harvest day) still had 18% THC and was pleasant enough while she lasted. We came out of that experience with an excellent knowledge of how to treat a plant with mold issues.
But the real key is to not allow it to start. To that end, we do the very best we can.
Sometimes, however, nature will not allow for your best plans. Two years ago, we were having a breakthrough grow. Spraying Regalia every other day had solved the powdery mildew problem and we were looking at a potential banner crop. Seven plants were already harvested, and five remained, when a large rainstorm was suddenly in the five day forecast.
Footnote: I am a weather nerd. Been one since we moved here. I have a weather station in the garden that reports to a computer inside. I track everything, because it is vital to what I grow. If I get hit with a weather event that causes me problems, that is entirely on me. When I see an increase in humidity coming, I ramp up my foliar sprays, sometimes to every morning, to get us through. An effective home weather device is another important cost, somewhere between $200-$300.
In this case, a multi-inch rainstorm, required immediate action.
I’m a grower who generally loves the rain. I view it as nature’s fertilizer. At any point during vegetative growth, I welcome rain. It is a gift. Even during the flowering phase, anything under half an inch is probably ok, though if I know half an inch is coming, I’ll still probably cover each plant with plant cloth, just for some protection.
But when a big storm is coming, and you are within days of harvesting the remainder of your crop, you have a choice: Protect your plants or harvest early. A massive rainstorm at that point can destroy your crop. We had to act fast. I literally saw the forecast of a large storm in five days, and I ran to the beds. I grabbed a tape measure and got the exact dimensions of our growing space. I went online and fortunately found a tarp in the exact dimension. It took a couple days to arrive, but when it did, both our sons came home to help. Below, you will see a series of photos of our sons, Brenden and Ryan, taking care of business.
Note the soon to be replaced, one gallon pump foliar sprayer in my hands.
After the tarp was on, rain poured all around us, but did not touch the plants. Doing this saved the majority of that crop, but not all. In putting this tarp over our grow, we protected it from rain, but increased the humidity UNDER the tarp by some exponential factor. Even with fans carried from the drying cottage out to the beds and turned on full blast. The tarp remained on for two days. We lost about 25% of two remaining plants to mold, because it was near impossible to inspect plants for mold in such diffuse light. As soon as the tarp came off, we had many cuts to make, including almost entire flowers. But the rest of the plants were saved.
I am grateful we have a tarp at the ready for when this happens again. And it will.
There are many factors that cause mold during the flower phase. Scat from any number of insects, dead or alive. Plant debris that blows into the garden from other plants and gets stuck on cannabis can rot and mold. We search every flowering plant every single day for debris. We have long handled tweezers for reaching into flowers and removing whatever needs to go.
So, a bad cut, a poorly sealed cut, a wayward piece of debri, a rotting insect, or a tiny piece of caterpillar or beetle scat can cause mold. I’m certain there are other causes I’ve yet to discover. There is no way you can find all of it in the beds, no matter how hard you work. That is why we ultimately wash each plant, as a final insurance against any pathogen entering our bodies. Next up is a blog about Beneficial Insects and Plants (with Action Photos!).