Mg def, or light intensity?

[Olderfart]

Could use some help interpreting this leaf color:

Details:

Autopots with ~3 gal fabric pots
EC ~1000 since reservoir topup three days ago, ~850 previously
pH 6.0-6.2 since last topup, 5.8-6 previously
Epsoms foliar four applications since last topup.
Full cal mag dose in nute mix since last topup, 2/3 dose previously
~480 total watts from wall, 46" from CQ, 42" from 24C; not recorded previously, but ~500 watts and closer by at least a few inches, mix of 5500K and 2700K screw in bulbs.

At last reservoir topup, I noticed this leaf coloring on new growth and figured it was Mg deficiency, light burn, or both. I backed off with light intensity, upped the mix to full cal mag and higher EC, and started foliar Epsom's.

My take now is that since new growth is still coming in with this color pattern in spite of full cal mag in mix plus foliar Epsom's, the problem is more likely to be that my light intensity is still too high. The plants are still growing well, but the color does not seem right to me.

@Waira and anyone else with applicable experience, I would appreciate hearing what you think. Thanks for any help you can send my way.

 

[Simplicio]

I vote for light burn.
There should be no deficiencies with any good fertilizer used correctly, with correct pH.
I'd back the lights way off for a few days, and see what happens.

 

[Olderfart]

Thanks for the quick reply Simplicio, I will likely do exactly that. I thought that I had already reduced light enough, but apparently not. I just don't see the Mg being the problem at this point. With full cal mag and foliar for the last three days, the new growth should have sorted if Mg were the culprit.

Anyway, I will see what else I generate in the way of opinion here, but unless there is argument otherwise, I will dial the light back another major notch before bed tonite. Thanks again for chiming in.

 

[iampepe]

If the symptom is only on the outer growth, Id say its light burn. If lower and inner leaves look the same than Mg deficiency.
Happy Growing!

 

[Olderfart]

If the symptom is only on the outer growth, Id say its light burn. If lower and inner leaves look the same than Mg deficiency.
Happy Growing!

All on new growth high on the plants. Lower stuff and shaded stuff looks normal. I already dialed the lights back to ~250 watts, and lifted them as high as they go. Part of the problem is that the plants are stretching like mad, so distance from lights has been dropping while I have been trying to sort this out.

Anyway, I will see what less light accomplishes.

Thanks for the reply Iampepe, I appreciate it.

 

[iampepe]

All on new growth high on the plants. Lower stuff and shaded stuff looks normal. I already dialed the lights back to ~250 watts, and lifted them as high as they go. Part of the problem is that the plants are stretching like mad, so distance from lights has been dropping while I have been trying to sort this out.

Anyway, I will see what less light accomplishes.

Thanks for the reply Iampepe, I appreciate it.

NP If you run out of room you can supercrop them without affecting the yield. Message the stem and bend it over.

 

[Olderfart]

NP If you run out of room you can supercrop them without affecting the yield. Message the stem and bend it over.

Done once already to tame a leader getting away from the others. Didn't tie it down however and the bugger was right back up there the following morning with just a minor kink in it. By which time most of the other leaders had pretty much caught up, so I left it alone. Anyway, the supercrop tool is in the kit, thanks for the suggestion.

 

[Waira]

Hey bud!
...so, the lights are 40+" away, and are they LED screw-in types? If so, IMO they likely are not the problem here,...
What I see looks like Zn defc., possibly Cu or Fe,... micro's in any case, all immobile, that's why the tops are hit first and worst... Mg is very mobile, it will be readily taken from lowers and it will show obviously...
What nutes are you using? ...ppm is pretty rich, but the actual content of micro's is in question......pH is fine (coco, right?)... how much ppm is coming from the Ca-Mg, BTW?
It's not Mg defc., no more foliars and heavy doses of Ca-Mg; too much of this and it can start to mess with the uptake of other cations....

...less light may make them stretch even more-

This calls for a micronute' supplement, best applied as a foliar and in the res'... If you are stateside, get some Earth Juice Microblast, wetting agent too if you don't have it already... I like Coco-Wet... be sure to spray undersides of leaves too, more stomatat there vs topside; do it during lights on, when transpiration is happening and the stomata are open....

 

[Olderfart]

Hi Waira, and thanks for hopping in. The nutes are Technaflora three part, hydroponic type stuff, and includes micros. The grow is in coco/perlite, strongly buffered with cal mag.

I would have to measure the contribution of the cal mag to the ~1000 EC, but it is large, maybe even half. I do not have quick access to the micro product you refer to - Amazon might have it, but not soon. I have some yucca extract on the way, but not here yet.

Given your advice, and the stuff I have on hand, this is what I will do for now. I have to top up the reservoir tonight, so I will back off on the cal mag to a half dose, and make up the diff with the boost/grow mix, pushing the mix toward the boost direction, and keeping the nute mix at ~1000 EC. I will also prepare a foliar of the boost side of the mix only, and apply that at ~700 EC.

I have from the beginning been puzzled how my grow lights could be the problem. I think they should behave roughly similar to most quantum boards of comparable power - both have widely distributed, small, and bare leds, and none of the quantum type boards to my knowledge require anywhere near the distances that I have been using recently. Given your take on this, I will move them back to ~30" for now, with only the 5500K bulbs active (this will keep power to ~260 watts for the time being).

Thanks for taking the time @Waira, I know that you put a lot of time in to the infirmary part of this site, and it is much appreciated. If what I get up to tonight seems like a bad idea to you, let me know and I will reload tomorrow.

 

[Olderfart]

Well, here's one for the lesson book. In the process of adjusting the nute mix to the new standard I had in mind, I found out that the EC in the reservoir was over 2000. The @#$!@#$!@ EC meter had apparently been accidentally on PPM, and yours truly did not notice. I guess that the mode switch between EC and PPM is a tad tight to the power switch for my stubby fingers. It is possible that the plants have been on 2000EC for the last two reservoir top ups, or the better part of a week. Annoyed, me? Maybe just a bit.

Anyway, the reservoir and feed lines are now all full with the intended solution, so I will watch for a few days to see how things go. My guess is that my screwup has caused who knows how much mischief in the lockout department. Presumably it will be a while leveling out. I considered flushing with the proper nute mix, but figured the shock might do more harm than good given the EC difference. Better perhaps for the EC to move down gradually for a day or two as new mix is sucked into the pots. Plus, getting a lot of nute solution to the top of the pots at this point would be a bit of a challenge given the density of stems and leaves. Grumble. Not amused.