You're faced with a choice: sell compromised product or have processes in place to mitigate potential problems.
Sounds simple enough. Until the topic of spraying late in flower comes up. That's when things derail into controversy.
Spraying late is not necessarily the optimal scenario, but sometimes we are faced with challenges we didn't expect, and rather than selling a compromised product, we need a mitigation strategy.
There's a lot of folks that will tell you if you spray late, you've compromised your entire crop.
I'd counter that there is something to be said about cutting down a sanitized crop versus selling something that's been compromised, especially in a medical market. Late flower applications are becoming more and more common as growers get over the belief that it's going to torch your crop and ruin your product.
If you've got a mold or a disease outbreak in late flower, and you just let it ride like that, the product can potentially have mycotoxins from mold or carcasses from bugs or whatever.
Choosing to just let it go unimpeded is the worst way to go because that issue is going to proliferate and propagate itself in other areas of the garden. If we just let that flower get to the end and don't do anything about it, well, then nothing's killing that bug or mold or keeping it from getting into that next room. Or that next crop.
If you need a reason to do a pre harvest spray, think about that next crop while you're still trying to maintain the integrity of the one you're currently growing.
Pre-Harvest Spraying vs Post-Harvest Dunking
Cannabis is a lot like a rose growing in your yard.
When your rose is attached to the rose bush, that flower can get wet, it can get beat up and it doesn't bleach. But the minute you put those in a vase, if you get even as much as a drop of water on one of those petals, it starts to turn white.
Cannabis is the same way; you can do a lot more to it while she's still attached to the vine and see a lot less "damage" that you would see after the fact with a dunk. Plus, the biggest problem with doing dunks, even if it's a small scale grower, is that if you're using something like Zerotol or hydrogen peroxide or even citric acid, every dunk you do is going to be less effective than the one that preceded it because we're introducing contaminants to that solution.
If we spray, we have a consistent level of sanitation or application throughout the entire crop because we're not contaminating the solution as we go.
It's also a lot more labor intensive to do dunks because you have to test your solution, fill it up, dump it out, refill it. Sprays are the most effective way to disinfect a crop before you cut it down and get that uniformity that you need.
Spraying is Only Half The Battle: Clean Your Dry/Cure Rooms
For whatever reason, growers forget about these crucial post-harvest spaces. I'll go to commercial facilities that have spent millions of dollars on their irrigation, their lights, their building, and you go to the Cure Room, and it's a fucking broom closet with, like, a portable dehumidifier in the back of the facility. And when you ask them what the parameters are in that room, they can't tell you.
Remember, mold grows in a damp, dark environment (just like your dry and cure room).
So what I've been recommending to a lot of growers is to also utilize a chlorine dioxide, slow release gas product such as Garden Clean for commercial drying rooms. Because, let's be honest, commercial rooms are never empty. There's rarely enough downtime in a dry room to get a thorough sanitation.
They chop down. They empty it out. And then the next day there's plants in there again.
The nice thing about those chlorine dioxide packets is they treat the air and you can literally hang them up in your room so that every time a door is opened, even if contaminants are introduced into that cure room, they will basically be oxidized, rendered inert by the time they land on a surface and are able to flourish. And, at these low release rates, the chlorine gas has a negligible impact on the final product.
In a commercial setting, if we're talking half a percentile of terpene or THC loss versus having an unsellable product you have to throw away, I'll trade that half a percent for safe product every day of the week.
How big of an impact does late spraying have on potential problems as well as the final product?
It's hard to quantify how much it can reduce contaminants because it all depends on each environment as well as the initial pathogen load.
If it's a pretty clean environment, that 1:100 ZeroTol application could probably get your total CFU down to zero. But, if we're in an environment that is fairly dirty and has wooden benches and antiquated equipment, and room for contamination, that application could get you to a level that'll pass industry standards, but I can't promise it's going to be a zero.
Here's the thing about live crops: things are going to grow regardless of what you do.
If you've created a perfect environment for your plants, you've also created a perfect environment for pests. And, without any natural competition, they'll thrive if you don't have the right processes in place.
Make sure that whatever you're spraying is going to have the widest range of efficacy that it can.
There are some products out there that have limited efficacy against certain pathogens. One of the reasons I really like using Zerotol or Citric Acid for late flower is that they degrade into the inert byproducts. On the other hand, if you were to use hypochloric acid (which breaks down into salt), you're going to have leftover residual sodium on your leaves, a byproduct of you just trying to disinfect it. And salt doesn't taste good to smoke.
There's a 2% variance between sprayed and non-sprayed plants.
Based on the people I know who have run testing for me on sprayed crops compared to non, a normal pre harvest spray of ZeroTol at 1:100 before chop results in ~2% variance (on all aspects of the product including yields and concentrations) from a sprayed plant to a non sprayed plant. But it all comes down to the amount of passable material; the people I work with would rather trade 2% for 20 pounds of safe, sellable product.
Spraying late in flower is the most ethical thing a farmer can do.
A properly applied spray during late flower can help reduce overall CFU, avoiding controversial (and potentially harmful) post-chop remediation and radiation. I work with a few large growers here in Colorado that are hash producers. They do a pre-harvest spray with Zerotol at 1:00 rate, and they rent their remediation machine out to other people because they don't need to use it. If you have to have a remediation machine, you're planning for failure, which is not a good way to start.
Every other type of farmer has to disinfect their crop before it ever goes to market; The fact that cannabis looks at it as a faux pas is kind of silly, especially because we're producing a medicine.
If you grew tomatoes or cantaloupes or any other type of consumable, you would have to have a step in between you and the store where you're basically making that product safe for consumption.
By doing a pre harvest spray, you're subjecting the entire crop to the same disinfection parameters, so you can't ever be accused of trying to cheat a sample. And you're doing what every other farmer in America does by making sure that the product that you're putting out has been run through a process to make it safe for consumption.
Even if you haven't noticed a problem, a pre chop spray is an overall standard for consumable, commercial product.
Especially if you're subject to microbial testing.
"An ounce of prevention is worth a pound of cure."
It's an easy step to spray before you cut down. And that's going to ensure even sanitation throughout the entire crop. Plus, it'll allow you to sleep easy at night not having to worry about your consumers smoking something like aspergillis. A Zerotol application would kill any aspergillis living on the buds at that point in time; It's a nondiscriminate disinfectant. It will go after any yeast, mold, or fungi that's on that bud itself. And the best thing with Zerotol? When it's dry, it's done.
It really comes down to kind of weighing that balance of your end game: if you've got a lot of product at stake, a small change may not be as big of a sacrifice, whereas if you got four plants that you're hanging and you didn't have a problem, there's a chance it's not necessary and could be an unneeded extra step.
The moral of the story is I always recommend doing a pre harvest spray over cutting down compromised product.
No matter what the scenario is, I would rather see you spray before you chop down and have clean weed, than to chop down dirty weed and try to make the best of it. If you've got botrytis that popped up in Week 8, even if it's just in the top colas, if you cut that plant down and hang it, everything in that room is going to have botrytis by the time you're done curing because you didn't address it.
That holds true whether you've got 4 plants or 400.
4 Golden Rules for Spraying in Late Flower
"What do you spray in late flower?"
That's the first question I get after I've convinced a grower to consider a pre-harvest or late flower spray. And it's an important question, because if you spray the wrong thing, you're going to leave residue on your buds, cause visible burn to your plant material, and potentially ruin the entire crop.
Rule #1: Don't use any types of oils or soaps.
While these have good efficacy in earlier stages, if we coat our flower with oil, we're definitely going to compromise the quality and the flavor.
If you've ever seen an oil derrick burn on the ocean, think about that black acrid smoke that comes off as the oil burns. If you've got oils leftover on your final product, you're smoking a mini oil fire that can't be good to inhale. Look at your products and their listed ingredients. If it includes canola oil or corn oil or literally any "oil", and you spray it on your buds before you cut down, your bud is not going to burn clean, and that black smoke that comes off of oil fires is going straight into the lungs of the consumer.
The biggest pushback against spraying late is that whatever your spraying is going to stick around on the final product, but that's only true if you're using the wrong sprays.
The biggest hang up for a lot of growers is they don't want to be like, "Man, I've grown this crop for 14 weeks and now it's going to all taste and smell like garlic bread because I'm using Rosemary oil," or something like that. And that's an obvious issue you want to avoid.
Rule #2: When doing late flower applications, look at a product's efficacy versus residuals.
A product like Zerotol or Citric Acid is going to be a good product for late sprays because both are able to disinfect an environment and have the least detriment to the final product—to the terps, the flavor and the potency. And, it's "done" when it's dry, meaning there's not a whole lot of residual activity that's going to go on. Having that short lived activity is going to make the likelihood of the spray compromising a product's integrity way less.
Rule #3: Don't spray microbials in late flower.
As well as avoiding oils and soaps, growers should avoid microbials, too. Yes, there are some microbials that are awesome for fighting mold and mildew. But the problem is if you're in an environment where there's any type of testing or regulatory oversight, those required Total Yeast and Mold (TYM) tests don't differentiate between good and bad organisms. They just do total CFU counts. And if you're spraying in late flower to keep a bad pathogen away, but then pop hot for a good microbe, that's one step forward, two steps back.
Rule #4: Don't use RO water for sprays.
The most common mistake I see is that people will spray with reverse osmosis water.
As you may or may not know, reverse osmosis (RO) water comes out of the machine at 7.0 pH and supposedly 0 EC if everything's working correctly.
If we let that sit at ambient temperature and pressure for 24 hours, RO drops to about a PH of 5.5. That's pretty low, but it's still within range. But if we were to mix that 5.5 pH RO spray with something like citric acid or Zerotol—both acidic compounds—we're probably at a pH closer to ~3.0, and that can burn stuff. That's where I see hairs get singed. That's where I see leaves turn yellow. That's where I see margins get kind of crispy. It's because the plant was basically sprayed with acid and the grower didn't compensate for the fact that there is no bicarbonate content in that RO.
Typically, I recommend growers either spike their RO to about 0.3 EC or just use plain old tap water for their sprays.