Light burn consistently with cobs/strips after 5th week of flower at only 30k lux?

Hey guys,

I've been looking through some of my photos/journals of my flowering plants over the last year and noticed that a lot of my plants show what appears to be light burn after the middle of flowering. It's surprising because my measurements of lux at canopy are lower than what other people have reported.

I think it's light burn because:

• it only affects top leaves
• it stops getting worse when I raise the light

I have been using Vero COBs and EB strips and I measure lux at the top of the canopy with Dr. meter brand meters. 40k is max I can hit, and then after mid flower is over the max I can hit 25-30k.


Here are a couple of examples from a current grow of Black Raspberry Kush by Cannaventure. Vegged for only 21 days. I've noticed that Indica dom plants I grow tend to show the problem more pronounced.



You can see on the picture above that only the top sets of leaves show the issue. The further down the plant you go the more normal it looks.

Here is another plant in the same tent, just barely started to show the same symptoms until I raised the light:



The yellow stops spreading pretty much immediately with the reduction in light.

What confuses me though is why can I only hit 40k lux max before seeing issues? Based on what I've read on this forum, 40k should be about the minimum. I'm running less than 25 watts per sq foot with my current build using EB strips (gen 2). The strips do cover much of the tent so that might be partly why I get away with lower wattage:



Also wondering if it's normal for plants to hit a peak about 5-7 weeks in and then need less light?

Thanks for reading!

I donno if thats light burn, there is no leaf curl or taco. Usually the leaves will let you know they are getting too much light.

What are the leaf temps closest to the light?

Snob said:

I donno if thats light burn, there is no leaf curl or taco. Usually the leaves will let you know they are getting too much light.

What are the leaf temps closest to the light?

Click to expand...

I should have checked when I started seeing the issue, the light has been raised now about a week.

Ambient temp is 79f.

The plant with the most yellow has upper leaf temps ranging from 70-80f.

The other plants upper leaves are all 69-73f.

(Using IR thermometer for measuring leaf temp)

The fact the upper leave temps are similar to ambient in some places is a bit weird. I usually see them at least 5 degrees cooler than ambient.

Normally im the first person to say light stress but it doesn't add up with the lux your using.
Unless its a super sensitive strain.

Maybe its a copper def, rare as they are.

Also seems to be showing signs of N tox.

Plus heat stress. Which doesn't add up if your thermometer is correct.
But I don't see a circulation fan anywhere.?

What's it getting fed?

What are you using to measure the LUX?

coreywebster said:

Normally im the first person to say light stress but it doesn't add up with the lux your using.
Unless its a super sensitive strain.

Maybe its a copper def, rare as they are.

Also seems to be showing signs of N tox.

Plus heat stress. Which doesn't add up if your thermometer is correct.
But I don't see a circulation fan anywhere.?

What's it getting fed?

Click to expand...

I've seen this on the last 4 runs, though sometimes very mild.

They are in 4 inch rockwool cubes, automated top feed to waste using Dyna Gro full line at about 50%. This is a couple runs ago, but irrigation is setup something like this:





Rez is external, about 10 gallons. I measure run off of each individual plant and make sure it's only ever .2 EC higher than input at max.

I stopped using circulation fans, just exhaust at about 180 cfm in each tent. Tents are 2x2 feet, big passive intake on bottom. The exhaust is strong enough to keep the leaves moving if I look up through the intake vents.

Chip Green said:

What are you using to measure the LUX?

Click to expand...

I have these 2 meters which seem to measure almost same (same brand):

https://www.amazon.com/gp/aw/d/B07LF4BT8V



I'm using the first one mostly

Animatey said:

I've seen this on the last 4 runs, though sometimes very mild.

They are in 4 inch rockwool cubes, automated top feed to waste using Dyna Gro full line at about 50%. This is a couple runs ago, but irrigation is setup something like this:

View attachment 4617349



Rez is external, about 10 gallons. I measure run off of each individual plant and make sure it's only ever .2 EC higher than input at max.

I stopped using circulation fans, just exhaust at about 180 cfm in each tent. Tents are 2x2 feet, big passive intake on bottom. The exhaust is strong enough to keep the leaves moving if I look up through the intake vents.

Click to expand...

Well somethings a miss to have clawed tips, dark green leaves and all the other symptoms.
Never used dynagro, what EC do you feed?
You seem to have classic nute burned tips.

I would be adding back some circulation fans, even if its a couple of pc fans from underneath. The tops may not be getting air circulation causing micro climates around the leaf to be much warmer than the rest of your space. That's the only thing I can think of that would cause the plant to take up more N giving the claw and general darkness and also have taco leaves going on.
Other than that copper def does look a bit like that and can be induce more light stress reaction so possible a problem with the nutrients or the ph. I would recalibrate the meter to make sure its not ph been off.

The other reason I would be checking out copper is the sheer contrast of the edge to the middle, unlike light stress where it tends to look more like a mag def but higher on the plant.

Just throwing ideas at you really.
I have a dr meter too, run at around 65000-80000lux without issue. Its also way more common to see issues of light stress in veg when they are getting longer hours of light. So with it happening mid flower its another reason to look at the nutrients and ph.
Most people I know with strips can run real close.

Do you have a filter attached to that irrigation system? It may very well be plugged.

coreywebster said:

Well somethings a miss to have clawed tips, dark green leaves and all the other symptoms.
Never used dynagro, what EC do you feed?
You seem to have classic nute burned tips.

I would be adding back some circulation fans, even if its a couple of pc fans from underneath. The tops may not be getting air circulation causing micro climates around the leaf to be much warmer than the rest of your space. That's the only thing I can think of that would cause the plant to take up more N giving the claw and general darkness and also have taco leaves going on.
Other than that copper def does look a bit like that and can be induce more light stress reaction so possible a problem with the nutrients or the ph. I would recalibrate the meter to make sure its not ph been off.

The other reason I would be checking out copper is the sheer contrast of the edge to the middle, unlike light stress where it tends to look more like a mag def but higher on the plant.

Just throwing ideas at you really.
I have a dr meter too, run at around 65000-80000lux without issue. Its also way more common to see issues of light stress in veg when they are getting longer hours of light. So with it happening mid flower its another reason to look at the nutrients and ph.
Most people I know with strips can run real close.

Click to expand...

It is weird I can't run them closer.

I appreciate the ideas, I'm not real sure what to think of it.

I think the tops are OK temperature wise because when I hit them with the IR thermometer the buds themselves are about 10 degrees F below ambient temps. Not sure... When I used to run circulation fans though I saw a lot of leaf tacos and the serrated edges would stand up.

I have somewhat low humidity and the fans were really drying them out. Right now my tent is at about 36% humidity.

Im not trying to disagree with everything btw lol... I'm pretty stumped so all input is appreciated. I am considering some PC fans possibly. I don't like the 6 inch clip ons because I have seen reports of them being real fire hazards.

I usually max out around 1.0 EC because my medium is very small (4x4 inches of rockwool). When it dries to 50% saturation the cubes are at about 2.0 EC. I water about 7 times a day to keep the EC steady since the cubes dry out so fast.

I'm actually just now wondering if the limited root space is contributing to the problem. I did a grow about a year ago in 6 inch rockwool cubes and didn't have this issue... Was using veros at about 40k-50k in a flood and drain setup and even had one plant hitting 90k lux and never saw this issue...

My plants are pretty small though. I've seen much bigger ones grown in 4 inch cubes so I dunno. Tricky...

It does kind of look like copper def.

The bloom nutrient I use has .05% copper

Sade said:

Do you have a filter attached to that irrigation system? It may very well be plugged.

Click to expand...

If it ever fails I think they will die pretty quickly. The medium will be fully dried out in probably 6 hours or less. 4 inch rockwool cubes hold a good amount of water, but with my humidity low and the plants in late flower it would empty out pretty quick.

Thanks for the idea, I do check the drippers every few days to make sure they are flowing.

coreywebster said:

Well somethings a miss to have clawed tips, dark green leaves and all the other symptoms.
Never used dynagro, what EC do you feed?
You seem to have classic nute burned tips.

I would be adding back some circulation fans, even if its a couple of pc fans from underneath. The tops may not be getting air circulation causing micro climates around the leaf to be much warmer than the rest of your space. That's the only thing I can think of that would cause the plant to take up more N giving the claw and general darkness and also have taco leaves going on.
Other than that copper def does look a bit like that and can be induce more light stress reaction so possible a problem with the nutrients or the ph. I would recalibrate the meter to make sure its not ph been off.

The other reason I would be checking out copper is the sheer contrast of the edge to the middle, unlike light stress where it tends to look more like a mag def but higher on the plant.

Just throwing ideas at you really.
I have a dr meter too, run at around 65000-80000lux without issue. Its also way more common to see issues of light stress in veg when they are getting longer hours of light. So with it happening mid flower its another reason to look at the nutrients and ph.
Most people I know with strips can run real close.

Click to expand...

I gotta agree on copper deficiency. Totally looks and sounds like it after reading this. Good call man.

coreywebster said:

Well somethings a miss to have clawed tips, dark green leaves and all the other symptoms.
Never used dynagro, what EC do you feed?
You seem to have classic nute burned tips.

I would be adding back some circulation fans, even if its a couple of pc fans from underneath. The tops may not be getting air circulation causing micro climates around the leaf to be much warmer than the rest of your space. That's the only thing I can think of that would cause the plant to take up more N giving the claw and general darkness and also have taco leaves going on.
Other than that copper def does look a bit like that and can be induce more light stress reaction so possible a problem with the nutrients or the ph. I would recalibrate the meter to make sure its not ph been off.

The other reason I would be checking out copper is the sheer contrast of the edge to the middle, unlike light stress where it tends to look more like a mag def but higher on the plant.

Just throwing ideas at you really.
I have a dr meter too, run at around 65000-80000lux without issue. Its also way more common to see issues of light stress in veg when they are getting longer hours of light. So with it happening mid flower its another reason to look at the nutrients and ph.
Most people I know with strips can run real close.

Click to expand...

I have to strongly agree with this something in th PH or your drip system is clogged or not being properly gravity fed.

PadawanWarrior said:

I gotta agree on copper deficiency. Totally looks and sounds like it after reading this. Good call man.

How to fix Cannabis Copper Deficiency (Cu) Pics & Symptoms

Cannabis leaf edges and tips turning yellow? Copper deficiency can cause dark, shiny leaves with purple or blue undertones. Learn how to spot and treat it!

www.growweedeasy.com

Click to expand...

The only thing I can think of for copper is pH.

I did a 2 point calibration on my meter with fresh 4.0 and 7.0 solution and the rez is at 6.1 pH.

The run off of the plant in the picture has 5.7 pH.

The nutrients I'm using have copper in them so I don't know.

Here is another plant, same tent. This one shows no signs of yellowing below the top fan leafs.




I'm leaning toward light stress still, but not sure what would make them so sensitive.

The buds are pretty heavy, they are definitely still bulking up well. I have to use ties to keep them from falling over. This makes me think the roots are probably ok, but again I'm not sure.

Animatey said:

The only thing I can think of for copper is pH.

I did a 2 point calibration on my meter with fresh 4.0 and 7.0 solution and the rez is at 6.1 pH.

The run off of the plant in the picture has 5.7 pH.

The nutrients I'm using have copper in them so I don't know.

Here is another plant, same tent. This one shows no signs of yellowing below the top fan leafs.




I'm leaning toward light stress still, but not sure what would make them so sensitive.

The buds are pretty heavy, they are definitely still bulking up well. I have to use ties to keep them from falling over. This makes me think the roots are probably ok, but again I'm not sure.

Click to expand...

Those bigger buds closer to the light will need more nutrients than the lower buds, and so they might be using more copper than the lower parts. The big buds demand more and will pull shit outta the leaves if it needs more, and since copper is a more immobile nutrient, it kinda makes sense. I'm no master though. Just a guess.

Oh, and plant yoyo's are great for the fatties.

most definitely not light burn my man. Coreys on point i think...too high an EC is looking likely...

lukio said:

most definitely not light burn my man. Coreys on point i think...too high an EC is looking likely...

Click to expand...

So my tap is .3 EC and I feed at a total of 1.0 EC.

That means I'm only adding 350ppm of nutrients.

It's actually still possible I'm over feeding though because the media is so small. However, I measure run off a couple times a week and I never see high EC come out... I keep the blocks wet by feeding 7 times a day so EC should be pretty stable.

Not sure why it is just showing on the top part of the plant.

It is weird... I'm still not sure about anything, will continue to read other's suggestions. It's possible it has something to do with EC.

Maybe I'm locking out copper

Animatey said:

So my tap is .3 EC

Click to expand...

do you know what the 0.3 is? you might be runnin too much Cal and Mg...potentially

i run an RO filter so i know how much Cal and Mg im using because i havent had my water tested

lukio said:

do you know what the 0.3 is? you might be runnin too much Cal and Mg...potentially

Click to expand...

I haven't had a water test so I couldn't say for sure. Dyna Gro is pretty light on the cal, but I'm using an Mg supplement (mag pro) since it's part of the schedule.

My tap is only 150ppm so even if that was all camg it wouldn't be too much IMO.

I can't find a chart I've seen that shows what nutrients can lock which other nutrients out, but that might help.