Consistent problem at 5-6 weeks of flower. Yellow tips and margins

[MumenRyder]

Hey y’all, I’ve noticed a pattern in some of my grows that I was basically chalking up to light stress. Mainly I did thought this because it affects the upper growth almost exclusively, and tends to get better when I raise the light.

However, I’ve decided that I actually have no idea what’s going on

The symptoms:

• Bright Yellow tips on upper leaves
• Bright Yellow margins on upper leaves
• Shows up after 5-7 weeks flowering

Here is one plant about 6 weeks into flower:

One week later:

Here are two other plants in the tent that demonstrate more clearly:

Notice how below the second node, the leaves are 100% unaffected:

Here is previous plant I grew that really got out of hand:

Here are some things that I do that are not normal…

• I use pool shock, I used to measure but now just eye ball it. The plant that got out of hand was actually done with dutch master zone. I did find one article suggesting chlorine tox shows up as yellowing tips and margins. However I did measure when using Zone and Zone uses chloramine mostly and that plant had the worst case.

• I water my 4 inch rockwool cubes 7 times a day including for 1 minute in the middle of the night. These guys dry out very fast.

• I stopped using circulation fans and rely completely on my exhaust fan

• I never go above 1.0 EC in the rez, and my tap water makes up .3EC

• I can’t break 40k lux, and usually have to limp to the finish at about 30k lux at canopy. This doesn’t seem normal, when I talked to other LED users they usually measure 50k minimum lux.

I’m using DynaGro brand nutrients.

The plant that got out of hand was done using vero COBs, the others with EB strips

My plan for my next grow is going back to 6 inch rockwool cubes, adding back circulation fans, going back to GH 3 part and using minimal H202 if my rez starts to smell.

If that doesn’t seem to get rid of the problem I guess I will have to try an HPS as I am just stumped with wtf could be going on…

Any ideas?

[anon5325009]

I’m also running 4 rockwool cubes with dynagro nutrients and I don’t get the same problem, then again I’m using HID lights.

[Shadey]

Looks like bad nitrogen toxicity, leaf tips are clawing and twisting, it’s affecting all leaves as it progresses.

Light burn usually affects just the tops, as you are using bottled nutrient, it should be balanced, so no deficiencies provided the water PH is ok.

Is it the same strain as last time that had this problem

How to Identify & Fix Cannabis Nitrogen Toxicity (with Pics)

[George]

Maybe you’re right but as it appears in the new growth I would look for an immobile deficiency, perhaps Zinc according to this picture …

[Craigson15]

Agreed, dont think its N tox but …

[George]

Do you have Mulder’s mobile number? Quite tough for me to interpretate that chart and have valid conclusions …

[monkeyman]

You mention EC but what about PH? It appears to be too alkaline by the way the leaves look, and that may be what is locking out some of the micronutrients

[ifish]

dynagrow bloom 3/12/6
K def
Maybe
: )

That chart looks like something moulder and scully would be investigating lol

[George]

@ifish

That chart looks like something moulder and scully would be investigating lol

He would finish with gray hair!

[ifish]

Could be light stress also : ) probably that , like you say only on top two nodes of fans

[ifish]

@George , looks like a symbol aliens would create on a corn field : )

[MumenRyder]

@anon5325009

I’m also running 4 rockwool cubes with dynagro nutrients and I don’t get the same problem, then again I’m using HID lights.

Are you growing in 4x4x4 inch cubes? How often do you water? Top feed or flood and drain?

@Shadey

Is it the same strain as last time that had this problem

Different strain, has actually happened all 4 times I’ve run a similar setup. The other 2 times the symptoms were much more mild and those strains were more Sativa. Not sure if that was what made the difference or not.

@Craigson15

Agreed, dont think its N tox but …

@George

Quite tough for me to interpretate that chart and have valid conclusions …

If it’s zinc, then that would be calcium locking it out (according to the mineral wheel), but my bloom nutrient is actually kind of low on calcium and it’s the only bottle that has any:

@monkeyman

what about PH?

My pH is good, I’m pretty religious about calibrating my meter, storing it in storage solution and I check pH of my rez and run off.

@ifish

Could be light stress also : ) probably that

It’s a definite possibility since it mainly affects upper leaves, but I’m not sure why I see it at such low levels of light. Usually for strips and COBs the minimum people read is about 50k lux, but I can’t break 40k without seeing issues.

[George]

Found something interesting … LINK

[ifish]

Ideal ratio for cal and mag is 2:1
Dynagrow 2:0.5

[MumenRyder]

The other bottle has more Mag in it. Mag Pro is a mag supplement that I use at 50% of bloom

[MumenRyder]

I think if it were Zinc then it would be Ca locking it out. My tap water is pretty soft and my nutes don’t have much Ca in them. It does kind of look like Zinc though…

[ifish]

From HPS to LED Growing Cannabis - Dutch Passion Blogs

Second pic : )
Raise your lights maybe ( I know nothing of led tho )

[MumenRyder]

Sort of, but I’m not sure. The leaf tips and margins there are real brown and burned, these are bright yellow and tend to stay that way until harvest

[Stickyjones]

I would reccomend trying something other than chlorine/chloramine to regulate ph. There is not a whole lot of info on its affects on cannabis but i did see that levels above 20ppm chlorine can cause burnt tips and yellowing leaves and that it can build up in the plant causing problems

[Craigson15]

Haha sorry I figured everyone had seen Mulders chart before.
But ya high N can cause other elements to be blocked too