Defoliation - Yield isn't everything

ScienceGrow

New Member
First let me state that most of this is written from what I remember reading when I went on a research binge. I can't recall all of my sources. But they were all free and available on the web, and were mostly from journals, universities, and expert organizations. I will link the few I can find at the bottom for your review.

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Defoliation: Yield isn't everything.
First, let's look at the classic motivation for defoliation. We won't be here long, there's more to see.

Proponents of defoliation generally cite higher yields as a benefit of defoliation, and it is this particular claim that is most in contention.

Opponents often invoke reduced photosynthetic activity as their reason against defoliation. The argument goes: more light, more leaves, more energy, more nutrient reserves, more yield.

Opponents are correct in their belief that photosynthetic activity is generally reduced by medium to heavy defoliation. Experiments involving defoliation and its effect on yield in many diverse plants have shown a consistent, causal link between defoliation and reduced yield in field-grown plants (outdoors.) This decrease is attributed to plant stress and decreased photosynthetic activity.

An exception in which yields increase is when the leaves removed have begun to senesce and have become sinks on the plant, rather than sources.

Typically, these older, larger fan leaves have lost efficiency with age. Opponents of defoliation often use the solar panel analogy. More and bigger solar panels mean more food for the plant. However, just as solar panels from 10 years ago are less efficient than those produced more recently, leaves also lose efficiency as they age. Leaves can begin to require more energy to stay alive than they produce. At this point, they are energy sinks, just as buds are. Unfortunately, buds as sinks produce a desired product; leaves do not. So at this point for the leaf, it is ALWAYS beneficial to remove them.

Many opponents of heavier defoliation are more accepting of such defoliation and removal of old fan leaves is a common practice.

Another exception in which defoliation is likely to increase yield is when the canopy is relatively uneven and bud sites are not receiving intense, quality light due to excess foliage and limited space. A plant that already has optimal conditions including quality light exposure is very unlikely to increase yield via defoliation, and in fact will likely decrease yield due to the decreased photosynthetic activity. A plant that is in a small space with little room to stretch and reach for a limited amount of light can indeed benefit greatly from even extreme defoliation, all other things being equal.

Hardcore opponents of defoliation sometimes mock defoliators with statements like "its basic plant science. If you cut off leaves, you decrease growth."

While they're right that this is a basic rule for plants, there are other, more advanced, and more difficult to understand exceptions to those rules.

In fact, defoliation is capable of an increase in photosynthetic performance, and can even overcompensate, and produce at a higher rate than before defoliation. Plants are life and life is complex, we need to think further than the basics. Basics of growing plants are Light, Water, and Soil. Now you tell me, is that REALLY all a plant needs to survive, and thrive? I think most of us know better.

If we really want to push our plants, we need to know their limits, and find the right balance between pushing them too far, and not enough.

Beyond Yields
While defoliation is unlikely to improve yields in plants living in optimal conditions, it may have other beneficial effects to plant development and final product. Defoliation in nature is actually very common. Whether it is caused by spider mites, caterpillars, deer, or some other pest, green foliage is a common target for herbivory, and there is no shortage of such pests. As stated above, defoliation is, with noted exceptions, generally bad for plant growth.

To adapt to the dangers of defoliation via herbivory, some plants have developed defensive measures to better ensure plant survival and reproductive success.

One of these defenses is the production and release of volatile chemicals in the plant. In addition, some of those volatile chemicals are the same chemicals that make our plants smell so amazing. Terpenes.

Release of Volatiles as a Defense against Herbivory
(While the literature cited will often refer to volatiles in general, terpenes are the subject at hand. I will be referring to volatiles as terpenes throughout this paper to keep things simple. Please read source materials for more specific scientific language.)

Terpenes are present in varying degrees in many healthy plants. However, when plants are damaged or defoliated through herbivory, particularly from insects and mites, the levels of terpenes and other volatiles are substantially increased in response to the damage.

This increase in volatile production, including terpenes, is most often used as a signal to repel pest insects, or more commonly, to attract the enemies of pest insects.

This effect appears to be systemic, meaning; infestation on an individual branch will elicit terpene production in distal, undamaged branches.

Furthermore, it is believed by some that this signaling process may even induce terpene production in other plants, though I have no actual data on this.

In some plants, like the lima bean, foliage destruction by spider mites causes an increase in terpene production. The benefit to this intriguing adaptation is that the increase of terpenes, and the type of terpenes, serves as a signal to predatory mites that a plant is infested with spider mites. This attracts the predatory mites to the plant, thereby benefitting the plant by, essentially, calling in backup. Many, many other examples of this are seen throughout nature.

Interestingly, spider mite damage induces the plant to develop terpenes specific to spider mites. Damage from caterpillars causes different terpenes to be produced in differing amounts in the affected plant. Each terpene mixture appears to be tuned to specific attackers. This of course benefits the plant by allowing it to call for the right kind of backup. Instead of a simple 911, it calls the fire department when there's a fire, the cops when there's a burglary, an ambulance when there's an injury. It tunes its call for help to the threat, allowing it to better survive the attack, and better propagate its genes.

Modifying/Enhancing the Terpene Profile
"An undamaged plant maintains a baseline level of volatile metabolites that are released from the surface of the leaf and/or from accumulated storage sites in the leaf. These constitutive chemical reserves, which often include monoterpenes, sesquiterpenes, and aromatics, accumulate to high levels in specialized glands, or trichomes.” - Quote from this article

As fascinating as plant defense mechanisms are, we're probably less interested in what terpenes do for the plant, and more interested in what terpenes do for us.

We often want to maximize terpene production to ensure bold and persistent flavor and aroma, and potentially other beneficial effects.

In fact, it's already recommended throughout the web that, minor manual defoliation can help increase terpene concentration. However, we appear to attribute this simply to stress, without further investigation or precise definition.

The effect of manual defoliation via cutting or pinching appears to generate a defensive response including terpene production increase. Yet, we now know that different attackers elicit a different terpene increase than others. They're tuned to their attackers. Therefore, while we may increase terpenes via mechanical defoliation, we may not be increasing the terpenes we want.

So, is it possible that through better simulation of defoliation via herbivory, specifically insects and mites, that we can not only increase the amount of terpenes, but also in fact control which terpenes are being produced? It would appear that this should be the case.

How do we go about simulating, say, spider mite damage then?

It isn't as easy as poking tiny holes in the leaves and leaving webbing all over the place, which is what we see mite damage as. Again, plants "know" the difference between attackers. Without intelligence (I'll debate that another time), cause and effect are the only viable explanation for how. There must be something else going on, telling the plant that a spider mite is biting it, vs. a caterpillar. Most likely, and as shown through experimentation, the insect, through their bite, inadvertently tells the plant what kind of insect it is.

More precisely, this appears to be caused by compounds found in the insect, imparted to the plant through regurgitation or injection, or some other method of transmission. A chemical in the “saliva” of an insect interacts with the volatiles in the leaf, and "tunes" the reaction to the insect.

Insect induced terpene production however, may not be long lived, as volatiles appear to be released quickly and are then gone. This would limit our ability to manipulate the product, and means we would likely need to wait until immediately prior to harvest to induce such effects. I have not been able to determine whether terpenes accumulate. If so, treating plants to spider mite damage over time may benefit from the cumulative effect. Much research is required on this.

In addition to this limitation, is the fact that volatiles including terpenes tax the plants metabolic system, either through production costs, or through potential damage via pollution of volatiles? This is yet another reason why we would want to wait until just before harvest to induce such stress on the plant.

Further research and experimentation is required to determine an optimum time to stress the plant in this manner. My prediction is the greatest effect, if any at all, would be within the last five hours preceding harvest. This is little more than a guess, but that’s what a lot of the wisdom on these forums appears to be.


Methods of Simulating Herbivory
In attempts to grow plants exactly as we want them, we exploit many of the survival mechanisms plants have developed. The most readily obvious is forced flowering. We can force a plant to move to another phase of its lifecycle by manipulating its reproductive signals into thinking it’s getting closer to the end of its life, it is time to start flowering.

We can increase THC content by introducing UVB. We can increase THC by simulating drought conditions. Minor tissue damage and defoliation are used to increase potency, yield, and smell, by many growers.

Most of these methods are relatively non-destructive and serve to benefit the plant as a whole. Introducing actual spider mites to the plant ecosystem would be considered by most to be of detriment, regardless of the benefits to terpene production. So, how can we attain the benefits of herbivory on terpene production, without encountering the detrimental effects?

1. Chemical Isolation
Under the best circumstances, we would be able to determine the unique triggers chemicals in each insect, isolate the important substances, and use these on the plant to direct terpene production. This has already been performed in the lab on some plant and insect species, with successful results in inducing terpene production, with the result of attracting predatory mites (in the case of spider mite infestation) and parasitic wasps (in the case of caterpillars.)

Unfortunately, we don't yet know what most of these insect compounds are, or how they interact with the plant. Synthesis of terpene inducing compounds introduced to plant damage points is unlikely to be a method of terpene regulation until such research is conducted and refined.

2. Simulation
Recently, an experiment involving the sound of a caterpillar eating a leaf was shown to induce volatile production to produce a substance toxic to the caterpillar. If this is the case, it is possible that identifying the chemicals involved may be unnecessary, and we may be able to stimulate terpene production without ever touching the plant. I find this to be an unlikely avenue to success, but it is worth investigation.

3. Sacrificial Limb (my favorite)
Fortunately, most methods of stress induction, including defoliation, appear to have systemic effects. In other words, we don't need to introduce spider mites to our entire plant to increase terpenes, we could introduce them to only a single branch, and use some form of physical isolation to prevent their spread. Once there is enough damage to elicit the desired response, complete removal of the limb can safely be performed, reducing risk of further infestation.

Furthermore, additional stresses on the same limb could be imposed, such as intense UVB exposure, wind damage, limb breakage, excessive localized light, heat, cold, etc.


Conclusion:
Defoliation is often regarded with contempt, especially when referenced as a method to increase yield. While defoliation under optimal conditions is very unlikely to have a positive impact on yield, defoliation at varying levels of severity can in fact increase an otherwise smaller yield. This almost entirely appears to be an effect of more exposure to quality light. However, some research has shown other pathways to greater yields, such as photosynthetic overcompensation. Unfortunately, these cases appear to be rare exceptions to the rule.

Defoliation has been presented in forums, briefly and without explanation, as a way to increase terpene production in the past. We now see that many species of plants do in fact increase terpene levels in response to defoliation, especially via insect herbivory and different levels and types of terpenes are expressed dependent on the attacking pest.

Control of terpene production is potentially possible through the simulation or controlled application of pest damage, or better, through the direct application of chemical elicitors derived or synthesized from the pest insects.

It is worth exploring through experimentation the level, quality, and stability of terpene compound production through insect herbivory simulation.

Finally, it must be noted that, there may be absolutely no benefit to final terpene content of our buds through this method. It is possible that the terpenes produced aren't the ones we would want, making it taste horrible.
It's possible they wouldn't be retained long enough to make any difference after drying/curing.
It's possible the levels accumulated wouldn't be significant enough to make a difference.

Again, I do believe it is worth exploring, and I'll be doing so in a future grow. Depending on my results, I may abandon this line of research, or investigate it further.

Discussion:
We tend to look at plants from an anthropocentric or egocentric point of view. We think of them from a "What does this plant do for me?" mindset. This is obviously how we should typically look at plants in our daily lives, but when attempting to manipulate nature to do your bidding, it is often beneficial to think from the plants evolutionary "point of view." When attempting to manipulate the plant, we need to think, "Why is the plant doing for itself?” Why is the plant green? Why is the fruit red? Why are their trichomes? Why does it smell? Why is there THC? How did these attributes benefit propagation or survival (for the purpose of propagation?)

You may notice all of my citations deal with all types of plant except Cannabis. I did this for a reason. There’s just not enough actual Cannabis science out there yet, so finding actual studies by qualified people is very difficult indeed. Mostly, you’ll find links to cannabis forums, where there’s a raging debate and no evidence but anecdotes.

Plants are plants, and while they all have their unique traits, they probably share more traits than not. While there is variation among plants in response to things like defoliation, plants respond overwhelmingly the same. So, learn more about plants in general.


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Some of my sources. Apologies for any that are just abstracts. While not very informative, they serve to confirm the results of some of the other papers I read.

Sources mostly on the effects of defoliation.
Wine grape defoliation
More wine grape defoliation
This is more about topping. Grapes.

For more information, check out your local library, get access to science journals, and search the web. Initially I used the term "Defoliation" but found that while they use that term, they also use more specific terms like Herbivory and Grazing, to essentially mean the same thing, partial or full removal of foliage.

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Let's discuss! Mostly the terpene stuff. Yield? I'll leave that to good environment and genetics.
 
Can't you see it? In 20 years we'll be buying special packages of live insects, with special instructions on how to infect your plant just enough to make the buds super potent!

It logically follows the above that experiments need to be done. Stressing plants via various insults and testing the terpene/ smokability response. If every stressor has a unique effect, we should figure out which if any of these effects enhances the high! I remember reading about various methods to improve weed quality, such as stripping the bark or splitting the plant at the base and putting a rock in middle of your plant's trunk.

If it is true that infestation in one place elicits a systemic response, that opens up all kinds of possibilities. Let's say that spider mites produce a beneficial effect on your weed. You would just isolate one budsite, infect that while sealing off the rest of the plant, then remove the spider mites at let your weed get juicy!

Timing obviously would be critical. You would think that a plant reacting to a stressor would be a pretty long term effect. But that would have to be tested, too. And of course when in the flowering cycle produces the best effect.

All things that probably can't get a serious look until after full legalization, when experiments like these can be pursued like other science, instead of being restricted by Prohibition.

A word on yield. The argument can be made that selective removal of plant tissue spurs a growth response that exceeds what the plant would have done without defoliation. After all, what is topping a plant? You are removing healthy tissue to spur a growth response. The key I think is what ways increase total yield.
 
Yeah undergrow, the sacrificial limb method seems like a simple enough way to go. Definitely need legalization so we can finally stop guessing.

Thanks thecelt.

I'll attempt photos tonight, but, I may have had an inadvertent experiment living in my flowering first grow.

Last night I was admiring my flowers, when I noticed a few little brown spots on a sugar leaf. At first it looked like bugs, so I looked closer. They weren't moving, so I looked even closer. That's when I saw webbing, inside a bud. Aww hell!

So I cut the bud and leaves off, and started prying the bud apart to see if it was mould or rot or actual webbing. And some little insect, not a mite, jumped out. It got away, so no chance identifying it. It was a light gray, possibly winged, about 1/4 long.

Anyway, hopefully it was the only one. Not seeing anything else.

But, upon closer investigation of those brown spots, I found that they were trichomes, overripe. My flowers are about 3-4 weeks in, so could be coincidence, but seems really early to be that dark.

Then again, it could just be bug feces. I need to go get that magnifier.
 
Its definitely early for over ripe trichomes but who knows what might have caused it. Could have been some sort of damage.

As for the bug, I've noticed a couple cocoons on my outdoor plants, and what might be one in the main cola of one of my girls. The main cola of that plant was stunted due to a mildew attack of the main stem. Cured the mildew problem but still waiting to see how she recovers before bending her over and inspecting the cola better.
 
Nice job Sciencegrow. :thumb:

If you were going to isolate a branch for a spider mite, how would you do it?

I have killed one of those grey/white winged insect, the texture of it is like a moth. I don't know what they are called because if i see it? i kill it, hahaha so i didn't bother looking it up.
 
Okay, probably just feces. Likely whitefiles.

Regarding how I'd isolate mites, I guess I'd need some kind of mesh bag that I'd place the mites in. Maybe take a plant from outside that has them already, place an infested cutting in the mesh bag, and strap the bag over the end of the limb, tying it tightly to the branch. Similar to hand pollinating. Leave the bag on there till the damage is done, and then remove the bagged portion of the branch with the bag still there.

I have six clones for my next grow and a bunch of seeds. Maybe I'll give it a go.
 
I noticed my extremely defoliated branches have a much higher concentration of trichomes on buds and sugar leaves than the rest.

So I did a search for defoliation and trichomes and found this:
Artificial Defoliation increases trichome production...

Get a free JSTOR account to read the whole thing, plus TONS more research papers.

Not cannabis, but, just more info and my anecdote. I'll be running experiments on my next grow, coming in a week or so.
 
I don't think any grower would willingly bring spider mites in their grow under any circumstances. No matter how many yummy juices the plant made. Those little f***ers would find a way to infest. They're like the ninjas of the cannabis bug world lol. But very interesting article. My experience has taught me that I don't cut a leaf unless it's more than half dead or blocking a bud. On a side note I know growers that completely defoliate anything not coated in sugar 24-48 hours before chop. They swear by it not so much for yield but aroma and taste. Maybe it's a stress reaction creating terpenes. That's interesting.
 
Stressing your lady out last two weeks before chop will put her in defense mode. It will make more resin production. For example, scrapping bark, tacks into branches, colder temps, lights go from 12/12 to 10/14 then 48 hours of darkness before you chop. THC is made by cannabis to catch male pollen. When she thinks she is dying then survival mode kicks in and more resin happens. I faithfully do it every grow last 2 weeks. And noticed my resin production go up a little but not a huge change but anything to enhance terps and trichs and resin.

Sent from my Robin using 420 Magazine Mobile App
 
instead of bugs, why not just start trimn a chunk off the leaves halfway thru flower? like everyday, just trim a fan off various leaves around the plant. Not the whole leaf, just a portion. I would imagine, the plant will think the same thing as a bug, *shruggs

or even take a tiny pair of scissors, and zigzag it like a small bug, BWJHAHAHAHAH

adding invasive insects is just, mindless.
 
Stressing your lady out last two weeks before chop will put her in defense mode. It will make more resin production. For example, scrapping bark, tacks into branches, colder temps, lights go from 12/12 to 10/14 then 48 hours of darkness before you chop. THC is made by cannabis to catch male pollen. When she thinks she is dying then survival mode kicks in and more resin happens. I faithfully do it every grow last 2 weeks. And noticed my resin production go up a little but not a huge change but anything to enhance terps and trichs and resin.

Sent from my Robin using 420 Magazine Mobile App

Yup ive always tacked my plants at the skinnier stalks and knifed the bigger ones. Dude. If your having pest problems there are two ways to go. Get some ladys, or prey. . are great for smaller pests. Preying mantisis are for bigger more pests. Also they work better if your indoors. My lady bugs are doin the fn job
 
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