Calling all PM experts. How do you deal?

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Frankster

Frankster

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I have to add here that we are unable to control the environment to any real degree. So we use it to our advantage. We know that plants thrive outside here, so we mimic it as best we can with open tents and enough fans to re-create the trades inside. (15-20 mph breeze we usually have.) We have had zero issues with PM or bud rot even though it is insanely humid often.
Exactly, tunneling air to create a choke point, so that your getting increased air flows. It's a brilliant strategy no doubt. I see this all the time standing among the tall buildings in downtown Seattle, especially around the corners. Your essentially increasing the evaporation off the surface of the plant by targeting the air flow.


Warm air can hold more water vapor than cold air. When warm, humid air is cooled, it can’t hold as much water vapor (RH rises), so the excess condenses into liquid water. That’s why cold surfaces “sweat.” Dew point is the temperature that will cause condensation or when the RH is 100%. The solution to condensation (sweating surfaces) is to reduce the relative humidity of the air (which lowers the dew point temperature) or keep surfaces warmer (above dew point).

Simply put, the higher your humidity, the higher should be your air movement. Heating the air (going into the fan) should also help.
 
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Frankster

Frankster

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A substance that has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape. the higher the temperature of the substance the greater the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.

Evaporation is a type of vaporization that occurs on the surface of a liquid as it changes into the gas phase. The surrounding gas must not be saturated with the evaporating substance. When the molecules of the liquid collide, they transfer energy to each other based on how they collide with each other. When a molecule near the surface absorbs enough energy to overcome the vapor pressure, it will escape and enter the surrounding air as a gas. When evaporation occurs, the energy removed from the vaporized liquid will reduce the temperature of the liquid, resulting in evaporative cooling.

On average, only a fraction of the molecules in a liquid have enough heat energy to escape from the liquid. The evaporation will continue until an equilibrium is reached when the evaporation of the liquid is equal to its condensation. In an enclosed environment, a liquid will evaporate until the surrounding air is saturated.

Evapotranspiration (ET) is the sum of water evaporation and transpiration from a surface area to the atmosphere.
Potential evaporation (PE) or potential evapotranspiration (PET) is defined as the amount of evaporation that would occur if a sufficient water source were available.

Factors influencing the rate of evaporation;​

Concentration of the substance evaporating in the air
If the air already has a high concentration of the substance evaporating, then the given substance will evaporate more slowly.

Flow rate of air
This is in part related to the concentration points above. If "fresh" air (i.e., air which is neither already saturated with the substance nor with other substances) is moving over the substance all the time, then the concentration of the substance in the air is less likely to go up with time, thus encouraging faster evaporation. This is the result of the boundary layer at the evaporation surface decreasing with flow velocity, decreasing the diffusion distance in the stagnant layer.

The amount of minerals dissolved in the liquid

Inter-molecular forces
The stronger the forces keeping the molecules together in the liquid state, the more energy one must get to escape. This is characterized by the enthalpy of vaporization.

Pressure
Evaporation happens faster if there is less exertion on the surface keeping the molecules from launching themselves.

Surface area
A substance that has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape.

Temperature of the substance
The higher the temperature of the substance the greater the kinetic energy of the molecules at its surface and therefore the faster the rate of their evaporation.
 
PizzaBob

PizzaBob

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So just chatting w a dude that has a nice sized outdoor garden and he always gets PM to some degree. He said H2O2 works best but burns the hairs up. Not sure how strong he mixes tho. Said it affects the look of finished product but it’s taking over a plant might be best plan.
His take is that not keeping on top of pruning the insides of these trees allows for it to get started and didn’t have fans. So to get through the season the poly is going up if it rains and putting in an industrial fan on the generator to blow down the rows.
 
radmobile

radmobile

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So just chatting w a dude that has a nice sized outdoor garden and he always gets PM to some degree. He said H2O2 works best but burns the hairs up. Not sure how strong he mixes tho. Said it affects the look of finished product but it’s taking over a plant might be best plan.
His take is that not keeping on top of pruning the insides of these trees allows for it to get started and didn’t have fans. So to get through the season the poly is going up if it rains and putting in an industrial fan on the generator to blow down the rows.
Here’s the recipe I picked up online in another forum - (works 100% of the time from my experience)

Application: Make a 0.5–2.0% solution (5–20 grams per liter) of potassium bicarbonate to water. Spray directly onto mildew infected plant tissue. Repeat weekly.

Cannabis Guru Ed Rosenthal’s formula uses an ounce of potassium bicarbonate mixed into a gallon of water and 1½ cups of milk.


The only issue is that it will burn out the pistils if the buds get sprayed. That being said, FOE20 (earlier in this thread) said I should follow the PB spray with washing down the plant with high ph’d water. I’m going to test this tonight on a few branches and see how it the pistils hold up. I’ll be back with my results!
 
FOE20

FOE20

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Here’s the recipe I picked up online in another forum - (works 100% of the time from my experience)

Application: Make a 0.5–2.0% solution (5–20 grams per liter) of potassium bicarbonate to water. Spray directly onto mildew infected plant tissue. Repeat weekly.

Cannabis Guru Ed Rosenthal’s formula uses an ounce of potassium bicarbonate mixed into a gallon of water and 1½ cups of milk.


The only issue is that it will burn out the pistils if the buds get sprayed. That being said, FOE20 (earlier in this thread) said I should follow the PB spray with washing down the plant with high ph’d water. I’m going to test this tonight on a few branches and see how it the pistils hold up. I’ll be back with my results!
"" You dont want more Moisture but your just using it fast as possible....you can do it without hitting budsites...you have to be careful...Foliage only...PM attacks leaves and will rest on stalks and shoots.""

avoid the budsites!!.....that is imperative...if you use a pump sprayer or even a hand sprayer just be careful to spray the infected areas Only on the Plant, stalk, shoots and foliage...
No Bud sites....power to it.
FOE20
 
Moe.Red

Moe.Red

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What are your night time humidity settings? I hear it’s good to get them down around 40? I’m somewhere up near 55.

my outside plants have it too. I feel like, if I’m going to spray my buds, I’ve ruined the entire grow. Other than High ph water (which didn’t help) everything has burned the pistils and ruined the quality.
Sorry about the outdoor stuff, I got no help there except be careful with the selection of genetics. Some plants seem impervious to PM unless you really neglect them. If I was outside I would seek those out.

My Dehuy is wifi controlled. Makes it really easy to make adjustments including day vs night with the timer function. But I don't do that, I set it at 50 veg - early flower and it does the rest. As I get towards end of flower I back it down to 40, and it never quite gets there, just too much respiration in my system with the fallponics, CO2, etc. The only way for me to reach 40% would be less plant matter, more dehuy, or unseal the tent and use the lung room to remove more water. None of those are options that interest me.

Screenshot 2021 09 11 at 10928 PM
 
Moe.Red

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This. Decreasing humidity all the time won't necessarily help, but keeping plants in VPD will. PM isn't just caused by moisture, it's caused by fluctuations in the temperature and humidity outside of proper VPD.

My flower room is at 60% humidity right now and I haven't seen PM in years. Humidity isn't the enemy with PM (or botrytis), an improper balance of humidity/temperature/airflow is.

The best preventative is proper VPD. The best treatment is micronized sulfur, sprayed regularly.
I agree with you, however VPD is a daytime only measurement, and IMO most PM gets a foothold at night.

I would be in complete agreement if the statement were amended to ... Proper VPD stuff you said..... and as low as you can reasonably make RH when the lights are off.

I haven't seem PM in years either but I have lost entire crops to it early on. Sux.
 
Kanzeon

Kanzeon

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I agree with you, however VPD is a daytime only measurement, and IMO most PM gets a foothold at night.

I would be in complete agreement if the statement were amended to ... Proper VPD stuff you said..... and as low as you can reasonably make RH when the lights are off.

I haven't seem PM in years either but I have lost entire crops to it early on. Sux.

I would agree, but my experience has been different. The times that I was hit the hardest with PM was when the humidity at night was super low, like under 20%.

According to @agseedco, when the plant is grown in in VPD during both lights on and off, the waxy coating on the leaf naturally protects it from things like PM colonizing. From what I understand, the process of growing under large diurnal shifts in areas with inconsistent airflow and humidity will wear off that waxy coating and make the plant more susceptible to threats like PM.

It's entirely possible there were other factors at the time that I didn't know about, but supplementing humidity during both day and night and keeping the leaves moving were the two environmental things that seemed to eliminate it for me for good.
 
PauliBhoy

PauliBhoy

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Horizontal airflow is usually adequate with moderate humidity levels.
Growers with high humidity levels should also use a sulfur vaporizer.
No need for sprays with an ounce of prevention.
 
Frankster

Frankster

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So just chatting w a dude that has a nice sized outdoor garden and he always gets PM to some degree. He said H2O2 works best but burns the hairs up. Not sure how strong he mixes tho. Said it affects the look of finished product but it’s taking over a plant might be best plan.
His take is that not keeping on top of pruning the insides of these trees allows for it to get started and didn’t have fans. So to get through the season the poly is going up if it rains and putting in an industrial fan on the generator to blow down the rows.
Agreed, I got a lot of small dense plants that I grow indoors, and if I don't stay on top of them they get so thick that problems develop. So I generally do a gentle defol in those cases, so better penetration of air movement and light is able to occur.

Buds end up more uniform, and the bottom generally ends up overall denser, with the added benefit of mitigating mold issues.

Any plant that doesn't have good penetration is certainly going to end up with not only potential mold issues, but larfy, useless buds in the regions that have been blocked by overgrowth.
 
Frankster

Frankster

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I agree with you, however VPD is a daytime only measurement, and IMO most PM gets a foothold at night.

I would be in complete agreement if the statement were amended to ... Proper VPD stuff you said..... and as low as you can reasonably make RH when the lights are off.

I haven't seem PM in years either but I have lost entire crops to it early on. Sux.
Agreed, it's usually happening in the late dark hours, when the dewpoint is lowest and relative humidity is usually highest. These two factors are conjoined at the hip so to speak.

I think this thread is useful, because it show's the newer growers how multifaceted PM and mold issues are, it's not any single factor, but multiple. So are the remedy, not any single thing to be done (especially when dehumid is removed).

Raising pH (PM and Fungus grow in acidic environments).
Increasing air flow throughout the plant or by thinning.
Use of mold inhibitors. Lactobacillus can be very effective in controlling diseases like Powdery Mildew. (I personally use lactobacillus acidophilus)

I also use UV light for this purpose (and increasing resin production)
A team of researchers led by David Gadoury, a plant pathologist at Cornell AgriTech in Geneva, New York, is looking into the control of powdery mildew using UV (A-B) light. ... The application of UV light at night can effectively zap the mildew's DNA and kill it.


Lastly, I would add being proactive, as once molds get any type of foothold, it's virtually impossible to control, the real keys here are prevention.
 
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shaganja

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Agreed, it's usually happening in the late dark hours, when the dewpoint is lowest and relative humidity is usually highest. These two factors are conjoined at the hip so to speak.

I think this thread is useful, because it show's the newer growers how multifaceted PM and mold issues are, it's not any single factor, but multiple. So are the remedy, not any single thing to be done (especially when dehumid is removed).

Raising pH (PM and Fungus grow in acidic environments).
Increasing air flow throughout the plant or by thinning.
Use of mold inhibitors. Lactobacillus can be very effective in controlling diseases like Powdery Mildew. (I personally use lactobacillus acidophilus)

I also use UV light for this purpose (and increasing resin production)
A team of researchers led by David Gadoury, a plant pathologist at Cornell AgriTech in Geneva, New York, is looking into the control of powdery mildew using UV (A-B) light. ... The application of UV light at night can effectively zap the mildew's DNA and kill it.


Lastly, I would add being proactive, as once molds get any type of foothold, it's virtually impossible to control, the real keys here are prevention.
Yes, I use uvb, and live in very humid area. Live 1 mile from lake huron, and 100 yards from a river that runs to it. Never get PM at my garden. I've seen a very small amount. Never been an issue so far.
 
radmobile

radmobile

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Yes, I use uvb, and live in very humid area. Live 1 mile from lake huron, and 100 yards from a river that runs to it. Never get PM at my garden. I've seen a very small amount. Never been an issue so far.
Using UV light at night doesn’t mess with plants in flower? I thought lights out means nothing but dark. How are you approaching this with UV lighting?
 
Mrb53

Mrb53

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I use, as a preventative spray, almost daily:
Dr. Frankenstein’s “It’s Alive” category - bio-animation spray. Bio-stimulant/Fungicide/Insecticide/Surfactant

Advanced Colloidal Micelles Nano-technology Insecticide and Fungicide uses USP grade oil, plant extracts, and organic acid mixed into colloidal micelles (supra-molecular surfactants). These micelles attract large particles using encapsulation. This encapsulation covers, maintains plant surface efficacy long-term, while increasing general plant health and BRIX score.

Pathogen removal - Removes mold and mildew by cleaning the plant and scrubbing it. Creating a slick surface that it cannot adhere. It will also destroy pathogens creating a clean plant surface. All this while scrubbing but not affecting THC

Some of the by-products are
Insect Control - Kills sap-sucking insects on several different levels: dissolves the exoskeleton, blocks digest enzyme production, and eliminates ability to digest the plant. These enzymes do not harm beneficial insects, so it can be used alongside beneficial treatments.

Bio Stimulant- healthier, thriving plants increasing systematic nutrient uptake. The micelles attach to fatty acids needed to process soluble and insoluble nutrients directly to the phloem and xylem of the plant, where it can increase overall plant health. contribute to foliar growth and enhance ripening.

Uses: For use on mold on cannabis or food grade crops grown outdoors, or inside, to controlling insects and rinsing residues...nothing worse than having any alternative remedies taining your bud and leaving aftertaste. I actually think this stuff makes my buds taste better

Controls the following Pathogens and Insects: Broad Mites, Russet Mites, Spider Mites, Aphids, Thrips, White Flies, Botrytis, Leafhoppers, Powered Mildew, Fusarium, Wilt, Downy Mildew, and other molds / mildews.

It can be used all the way to and including HARVESTING / DRYING stages
 
PauliBhoy

PauliBhoy

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Bottom line, the plant needs to be in that proper humidification zone, not too high, not too low. In a targeted range. When temperature, humidity controls go out the window, it makes this ever more problematic. In an outdoor setting, it seems to me that potentially air movement (fans) and osmotic concentrations (foliar) are regulating factors that can be potentially harnessed here, as we no longer control temperature, nor humidity.
This is because 99% of all the breeding work in the West has been done indoors for generations thanks to prohibition and, lately, misconceptions. Humboldt strains were popular because they were often selected for outdoor or greenhouse growing, where humidity levels (among other things) are often not optimal. Growers with imperfect conditions would actually have successful harvests.

Perhaps we should demand that our Cannabis breeders produce strains that are better adapted to sub-optimal conditions? The high-input-->high-output model is the race to the bottom. Surely we haven't lost all the really good genetics yet?
 

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