The Art of Differential Diagnosis

DocofRock

Well-Known Member
Good afternoon, RIU! I wanted to talk about the process of differential diagnosis for growing cannabis.

Differential diagnosis is a concept borrowed from the field of medicine that means “distinguishing a disease or condition from others that present with similar clinical features”. Let me give you an example.

A patient comes to the clinic with cardiac arrhythmias (irregular heart rhythm), a critically high potassium level, and rapid/labored breathing. This is the presentation of the patient and the symptoms they are expressing. What I just described, however, was NOT a diagnosis, and here is why...

A diagnosis is constructed based on examining the available information, seeking additional information if necessary, and ruling out potential diseases or conditions that present similarly but are due to completely different pathologies.

In the example above, this patient could be in kidney failure - causing a build up of fluid in the lungs (causing the rapid and labored breathing), an elevated serum potassium (glomerular filtration too low to remove electrolytes/fluid from the patient), and arrhythmia because of the electrolyte imbalances and hyperkalemia (potassium level too high). This patient could also be in diabetic ketoacidosis, causing the same symptoms, but for entirely different reasons.

Can we treat the high potassium? Sure. Will it do anything (let’s say in the example of the patient in diabetic ketoacidosis) other than mask the symptoms of the underlying issue? Absolutely not.

So wtf does this have to do with cannabis cultivation?

I’m glad you asked. As it turns out, cannabis plants, much like humans, animals, and other eukaryotic forms of life, are capable of immensely complex biological and cellular processes. Also similar to humans, cannabis wants to and will fight to live in the conditions it is given. Unfortunately, it is only possible for cannabis to be subjected to immense stress and inhospitable conditions for so long. And, as in humans, sometimes you don’t find out what really happened until the autopsy. Maybe if the doctor had really found the underlying disease causing all the symptoms of the patient’s illness, they could have intervened.

A simple, yet incredibly important thing to remember when it comes to growing: your plants’ reaction to and expression of problems are how the plant communicates a problem. As an example, wilting, dry leaves accompanied by nutrient toxicity are the symptoms displayed, but alone, these symptoms don’t tell you the problem. This is where differential diagnosis/critical thinking comes into play. The difference between a novice grower (or novice clinician) and an expert? The novice treats the symptoms, the expert treats the cause.

An example from my latest grow:

Everything seemed to be going fine in the grow tent. My plants were exploding and producing fantastic growth. My environment was within range (at least it appeared), nutrient ratios, pH, and concentrations were correct, and plants were not being overwatered or overwatered. One morning, upon waking, I noticed my plants had wilted, looking almost unrecognizable from the healthy plants I had seen when I went to bed. I knew it wasn’t overwatering or overfeeding. I religiously watch the parameters of my grow, pH everything that even gets brought into the grow room. I’ve been feeding only 650-750 ppm Max to 4 week old plants in coco, and nothing but water to my soil plants of the same age. I just couldn’t figure it out.... at first.

It turns out, in my inexperience with LED lights and my newness to growing indoors, I underestimated the strength of my lights. Worse, I didn’t understand the principles behind voltage, amperage, watts. I thought I knew my lights and, to the best of my ability, estimated the par/PPFD of my lights. What I didn’t understand was the principles of electricity or constant voltage drivers. It turns out, there was no physical way I could have reduced the par intensity using the two fixtures I have in the tent, because turning down the potentiometer and wattage of the lamps to the minimum allowable was STILL too much par energy. Way too much. And no matter how much I turned down the potentiometer, I was still not changing the PPF output much, just wasting electricity, creating heat, and stressing my plants. To figure out what I had ultimately done, I tapped the bank of knowledge I’ve acquired as well as researched. I know my stuff, but sometimes it’s easy to overlook critical factors in your grow, especially while you’re learning. By performing a comprehensive assessment of my plants, environment, and nutrient/water intake, I was able to make a deduction of the likely culprits contributing to my issues.

I could have just stopped feeding my plants, as they were displaying Nitrogen toxicity. As a result, they would have gotten worse, being underfed AND light/heat burned with a high VPD and underwatered conditions. However, it’s almost never as simple (and is usually counter-productive) to adjust a nutrient regimen you KNOW to be within an acceptable ppm/EC range. So WHY did I get the wilting, nitrogen toxic leaves? Well, a combination of things which on their own would not have caused an issue, but all together set off a terrible chain reaction.

My lights were a bit too intense, and a bit to close (even though the PPFD was within acceptable range, at least I thought). This caused a concentrated area of heat and light over abundance (even though the temp was perfectly normal if evaluated by itself - 77F). Coupled with my tendency toward underwatering (in my soil plants - scared of mold). Due to the high temp and light intensity, the vapor pressure deficit climbed to an unacceptable range, causing the plants to increase transpiration, creating dehydration in the leaves, and increased evaporation from the soil. Coupled with a soil with very high organic matter content (rich in N), a decreased ability to perform effective photosynthesis, and an increased need for water (which caused nutes to be taken up too quickly as well), the end result would have been disastrous if I was unable to accurately and quickly determine the issue.

If I can impress one thing upon you, it is simply to think through the situation to the best of your ability. Your plants almost always need a lot less of something you’re providing, and in my case, it was all from too much light. It’s the extremes (in environment/nutes/watering/air circulation or lack there of) that usually set of the chain reactions of negative events. Could the plant have dealt with any one of these issues in isolation? Sure, but there’s hardly anything that occurs in horticulture, medicine, or hell... life itself, that exists in a vacuum. So, if you want to grow good cannabis, back off of the excess and really learn the fundamentals.

As we continue to push the limits of cannabis horticulture, we fly closer to the edge. Lights are more powerful, information is more plentiful, and nutrient lines are more confusing than ever before. Have a problem with your plants? Figure out where you’re just doing too much using some good old fashioned critical thinking, and work on your differential diagnoses. On our perpetual quest towards “more” and “better”, often the answers lie in just getting back to the basics. We all likely smoked weed long before the time when there were 15,000 nutrient lines, 500 online forums, and 3.0 umol/J lighting fixtures. As it turns out, more is not always better.

As we continue to push the limits in cultivation, I foresee problems becoming a lot more frequent and much more confusing. It’s easier to fix a nutrient issue when your regimen consists of a few ingredients than a basket full. A simple feed schedule with adequate light, good air flow, and a well controlled environment will always do you better than adding additional and extraneous variables.
 

Jypsy Dog

Well-Known Member
Good afternoon, RIU! I wanted to talk about the process of differential diagnosis for growing cannabis.

Differential diagnosis is a concept borrowed from the field of medicine that means “distinguishing a disease or condition from others that present with similar clinical features”. Let me give you an example.

A patient comes to the clinic with cardiac arrhythmias (irregular heart rhythm), a critically high potassium level, and rapid/labored breathing. This is the presentation of the patient and the symptoms they are expressing. What I just described, however, was NOT a diagnosis, and here is why...

A diagnosis is constructed based on examining the available information, seeking additional information if necessary, and ruling out potential diseases or conditions that present similarly but are due to completely different pathologies.

In the example above, this patient could be in kidney failure - causing a build up of fluid in the lungs (causing the rapid and labored breathing), an elevated serum potassium (glomerular filtration too low to remove electrolytes/fluid from the patient), and arrhythmia because of the electrolyte imbalances and hyperkalemia (potassium level too high). This patient could also be in diabetic ketoacidosis, causing the same symptoms, but for entirely different reasons.

Can we treat the high potassium? Sure. Will it do anything (let’s say in the example of the patient in diabetic ketoacidosis) other than mask the symptoms of the underlying issue? Absolutely not.

So wtf does this have to do with cannabis cultivation?

I’m glad you asked. As it turns out, cannabis plants, much like humans, animals, and other eukaryotic forms of life, are capable of immensely complex biological and cellular processes. Also similar to humans, cannabis wants to and will fight to live in the conditions it is given. Unfortunately, it is only possible for cannabis to be subjected to immense stress and inhospitable conditions for so long. And, as in humans, sometimes you don’t find out what really happened until the autopsy. Maybe if the doctor had really found the underlying disease causing all the symptoms of the patient’s illness, they could have intervened.

A simple, yet incredibly important thing to remember when it comes to growing: your plants’ reaction to and expression of problems are how the plant communicates a problem. As an example, wilting, dry leaves accompanied by nutrient toxicity are the symptoms displayed, but alone, these symptoms don’t tell you the problem. This is where differential diagnosis/critical thinking comes into play. The difference between a novice grower (or novice clinician) and an expert? The novice treats the symptoms, the expert treats the cause.

An example from my latest grow:

Everything seemed to be going fine in the grow tent. My plants were exploding and producing fantastic growth. My environment was within range (at least it appeared), nutrient ratios, pH, and concentrations were correct, and plants were not being overwatered or overwatered. One morning, upon waking, I noticed my plants had wilted, looking almost unrecognizable from the healthy plants I had seen when I went to bed. I knew it wasn’t overwatering or overfeeding. I religiously watch the parameters of my grow, pH everything that even gets brought into the grow room. I’ve been feeding only 650-750 ppm Max to 4 week old plants in coco, and nothing but water to my soil plants of the same age. I just couldn’t figure it out.... at first.

It turns out, in my inexperience with LED lights and my newness to growing indoors, I underestimated the strength of my lights. Worse, I didn’t understand the principles behind voltage, amperage, watts. I thought I knew my lights and, to the best of my ability, estimated the par/PPFD of my lights. What I didn’t understand was the principles of electricity or constant voltage drivers. It turns out, there was no physical way I could have reduced the par intensity using the two fixtures I have in the tent, because turning down the potentiometer and wattage of the lamps to the minimum allowable was STILL too much par energy. Way too much. And no matter how much I turned down the potentiometer, I was still not changing the PPF output much, just wasting electricity, creating heat, and stressing my plants. To figure out what I had ultimately done, I tapped the bank of knowledge I’ve acquired as well as researched. I know my stuff, but sometimes it’s easy to overlook critical factors in your grow, especially while you’re learning. By performing a comprehensive assessment of my plants, environment, and nutrient/water intake, I was able to make a deduction of the likely culprits contributing to my issues.

I could have just stopped feeding my plants, as they were displaying Nitrogen toxicity. As a result, they would have gotten worse, being underfed AND light/heat burned with a high VPD and underwatered conditions. However, it’s almost never as simple (and is usually counter-productive) to adjust a nutrient regimen you KNOW to be within an acceptable ppm/EC range. So WHY did I get the wilting, nitrogen toxic leaves? Well, a combination of things which on their own would not have caused an issue, but all together set off a terrible chain reaction.

My lights were a bit too intense, and a bit to close (even though the PPFD was within acceptable range, at least I thought). This caused a concentrated area of heat and light over abundance (even though the temp was perfectly normal if evaluated by itself - 77F). Coupled with my tendency toward underwatering (in my soil plants - scared of mold). Due to the high temp and light intensity, the vapor pressure deficit climbed to an unacceptable range, causing the plants to increase transpiration, creating dehydration in the leaves, and increased evaporation from the soil. Coupled with a soil with very high organic matter content (rich in N), a decreased ability to perform effective photosynthesis, and an increased need for water (which caused nutes to be taken up too quickly as well), the end result would have been disastrous if I was unable to accurately and quickly determine the issue.

If I can impress one thing upon you, it is simply to think through the situation to the best of your ability. Your plants almost always need a lot less of something you’re providing, and in my case, it was all from too much light. It’s the extremes (in environment/nutes/watering/air circulation or lack there of) that usually set of the chain reactions of negative events. Could the plant have dealt with any one of these issues in isolation? Sure, but there’s hardly anything that occurs in horticulture, medicine, or hell... life itself, that exists in a vacuum. So, if you want to grow good cannabis, back off of the excess and really learn the fundamentals.

As we continue to push the limits of cannabis horticulture, we fly closer to the edge. Lights are more powerful, information is more plentiful, and nutrient lines are more confusing than ever before. Have a problem with your plants? Figure out where you’re just doing too much using some good old fashioned critical thinking, and work on your differential diagnoses. On our perpetual quest towards “more” and “better”, often the answers lie in just getting back to the basics. We all likely smoked weed long before the time when there were 15,000 nutrient lines, 500 online forums, and 3.0 umol/J lighting fixtures. As it turns out, more is not always better.

As we continue to push the limits in cultivation, I foresee problems becoming a lot more frequent and much more confusing. It’s easier to fix a nutrient issue when your regimen consists of a few ingredients than a basket full. A simple feed schedule with adequate light, good air flow, and a well controlled environment will always do you better than adding additional and extraneous variables.
 

xtsho

Well-Known Member
As it turns out, more is not always better.

As we continue to push the limits in cultivation, I foresee problems becoming a lot more frequent and much more confusing. It’s easier to fix a nutrient issue when your regimen consists of a few ingredients than a basket full. A simple feed schedule with adequate light, good air flow, and a well controlled environment will always do you better than adding additional and extraneous variables.
Most issues are caused by growers doing too much with their plants. Too many bottles of stuff they don't need. Too much fussing with things that don't matter, runoff pH in soil, etc...

All you need for a successful grow is to provide a good environment and to feed the plant what it needs not some magic potion in a bottle. Too many people get caught up with fancy labels, cool sounding names, false claims from manufacturers, and youtube videos that are either full of bad information or are just an infomercial to sell some overpriced product you don't need. As I watch people having all kinds of issues with their plants while using a dozen bottles of the latest greatest nute line and fussing with their plants 24/7 I continue to grow plants problem free without even bothering to look at them for days at a time. I've never used calmag, I've never flushed my plants, I've never checked pH runoff, etc... Unfortunately for many of the growers that have never grown anything other than cannabis their first foray into growing is a plant that has so much misinformation about it online that they are unable to differentiate fact from fiction. Nutrient companies, light manufacturers, and others in the industry spread so much fiction to sell their products that we now have a large amount of growers that use stoner science rather than plant science with terrible results.

If you look online for tips on growing tomato's, corn, flowers, or basically any other plant you will find plenty of legitimate information regarding growing those plants. With cannabis a good portion of information is not from actual individuals with valid knowledge but from sleazy marketers pushing expensive, overpriced, and unnecessary snake oil products on the naive.

KISS "KEEP IT SIMPLE STUPID"

Do that and most peoples grows would improve and they wouldn't be hanging out in the Marijuana Plant Problems section looking for answers and many times getting bad advice. Flush the plant, check runoff pH, add calmag, those are the three most common responses to just about every issue people have. Many times the best solution is to do nothing. Don't dump more stuff on your plants, don't drown them by flooding the grow media. Cannabis is a very easy plant to grow. It doesn't need much. It doesn't need five bottles of different boosters. It doesn't need sugar, vitamin, or amino acid products. Cannabis growers are being fleeced. Paying $25 for a bottle of diluted MKP that cost less than a dollar to make with 80% of that dollar going to packaging. I could go on and on. Some people get it but others are still firm believers in all the nonsense and buy into the nonsense that cannabis is special and needs all the crap being marketed. It doesn't. Cannabis is not special. It's not hard to grow. Cannabis is just another plant and one that is very easy to grow.
 

1212ham

Well-Known Member
My lights were a bit too intense, and a bit to close (even though the PPFD was within acceptable range, at least I thought). This caused a concentrated area of heat and light over abundance (even though the temp was perfectly normal if evaluated by itself - 77F). Coupled with my tendency toward underwatering (in my soil plants - scared of mold). Due to the high temp and light intensity, the vapor pressure deficit climbed to an unacceptable range, causing the plants to increase transpiration, creating dehydration in the leaves, and increased evaporation from the soil.
Plants need higher air temp under LED due to the lack of IR heating the plant. 77F is not high temperature under LED, around 82-85 is where they are happy. If VPD is out of range, adjust the humidity.
 

DocofRock

Well-Known Member
This guy gets it.

Plants need higher air temp under LED due to the lack of IR heating the plant. 77F is not high temperature under LED, around 82-85 is where they are happy. If VPD is out of range, adjust the humidity.
Even when growing heavily indica dominant as well as auto strains? Temp is 76 right now and they seem to be happy. I removed one QB260 kit and am vegging with just one QB260. I am glad my par meter is coming on Monday so I can get this lined out for proper PPFD and then tailor my environment around it. Plants seem to be back on track. Eventually these trimmed leaves will die, but for now, they are at least contributing to photosynthesis. All the new growth looks healthy to me.

C4B1DA36-5DF3-4E56-ABF4-B550BE07825C.jpeg
 

Geotropic

Member
What pffd or dli were you trying to get?

What are your lights and distance above canopy?

I want to use your info for my own analysis if you would be so kind to provide it. Thanks!
 

DocofRock

Well-Known Member
I was going for around 400 PPFD, around 30” from the plants. Found that was too intense still, and now I’m literally at the top of the tent with my 2 QB260 kits, turned down to about 140 watts each, and my plants are getting around 300 PPFD. My problem was also likely influenced by too high VPD. Here’s an updated pic.

C80E92D9-C3D4-4992-972A-0FAE0ECAF743.jpeg
 
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