Light Stress? Will adjusting nutes help?

So I think I am seeing some light stress in a couple of my Autos. Patches of rusty/brown/bronze only found on the upper leaves and what looks like burned tips of bracts/calyx at the very tops of the colas. Been a slow progression over the past week, thought it was nute burn or cal/mag deficiency at first but light burn/stress is the only thing that makes sense to me. Am i right? How bad does it look to you guys?

I've raised my LED a couple inches but am wondering if I should also adjust my nute mix at all? Could a nute imbalance or lack of P/K making the light stress happen or get worse? I've read that nute imbalance can trigger light stress, or maybe the other way around? Or maybe a deficiency I'm missing in the first place if fixed will allow for the plant to better handle the light? Or am I overthinking this too much and its just a light sensitive strain?

Grow details: Autoflower Canuk Quarter Pounder. Week 10 from seed, 5 weeks into flower. Growing in coco drain to waste using GH flora series @ 1EC / 5.5-6pH. Runoff often drift up to 6.5pH hence the fert at 5.5 sometimes. Under a 200W (actual draw) 440-660nm 3500k LED & 200W sunblaster CFL 3500k. Light distance to LED was 14", raised to 18" now. 6-16" from the CFL. Temps=20-24C RH=50-55%. Let me know if there's anything I'm forgetting to mention.

Any thoughts or advice would be appreciated. Thanks!

Forgot to mention Ive been using CalMag and Epsom salt the whole grow and liquid KoolBloom during bloom which is included in the 1EC.

Bump.

Anyone? I'm in a critical phase of flower here, want to maximize my harvest.

WintersBones said:

Bump.

Anyone? I'm in a critical phase of flower here, want to maximize my harvest.

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Why is your LED so close? Most manufacturers suggest far higher. Personally I would raise to 24” and keep the CFL close.

I don't run LED's so I have no idea in terms of how close is too close with a light like that, however, your plants don't look light stressed...even if your lights are too close (or maybe not, again I have no idea). To me it appears like simple deficiencies (P and K, and maybe even Ca), but your plants also look pretty far along in flower and they look pretty darn good. I'm not sure I'd be trying to fix those few little blemishes all things considered.

You may want to consider your Mg levels...feeding both CalMag and Epsom most likely has them pretty high in Mg which can lock out other nutrients, which may not be helping the situation. I would use one or the other, but not both.

Good luck

I'm still within the manufacturer's recommendations, between 12-18" for bloom (940-529 PPFD). But I'm definitely trying to push them to take as much light as possible. I've got two plants of the same strain doing this, only one is pictured but its exact same thing on both, they're like twins in every way, and two other strains in the same room/conditions that are looking fine at the same or even closer distance.

CannaCountry said:

I don't run LED's so I have no idea in terms of how close is too close with a light like that, however, your plants don't look light stressed...even if your lights are too close (or maybe not, again I have no idea). To me it appears like simple deficiencies (P and K, and maybe even Ca), but your plants also look pretty far along in flower and they look pretty darn good. I'm not sure I'd be trying to fix those few little blemishes all things considered.

You may want to consider your Mg levels...feeding both CalMag and Epsom most likely has them pretty high in Mg which can lock out other nutrients, which may not be helping the situation. I would use one or the other, but not both.

Good luck

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Ah thanks I hadn't considered too much Mg. I had some early Cal/Mag deficiencies due to a poor coco buffer so I've maybe been heavy handed with the Calmag and Epsom salts and also hearing the sulfur in it helps in bloom. just back off on the overall amount of CalMag and/or Epsom and leave everything else the same? Boosting the P&K a little worth it? (Im keeping the light raised as well) Thanks for the reassurance, my best grow yet and I don't want to mess it up lol!

WintersBones said:

Ah thanks I hadn't considered too much Mg. I had some early Cal/Mag deficiencies due to a poor coco buffer so I've maybe been heavy handed with the Calmag and Epsom salts and also hearing the sulfur in it helps in bloom. just back off on the overall amount of CalMag and/or Epsom and leave everything else the same? Boosting the P&K a little worth it? (Im keeping the light raised as well) Thanks for the reassurance, my best grow yet and I don't want to mess it up lol!

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Again, I'm not sure I'd try to fix a whole lot considering where you are in flower. If the CalMag is your only source of Ca, I would use it vs the Epsom, so you're at least getting both Ca and Mg into your mix. I don't use PK boosters so I couldn't comment on whether it would help or not. I tend to stick with the less is more approach, especially as one nears the finish line. Good luck.

CannaCountry said:

Again, I'm not sure I'd try to fix a whole lot considering where you are in flower. If the CalMag is your only source of Ca, I would use it vs the Epsom, so you're at least getting both Ca and Mg into your mix. I don't use PK boosters so I couldn't comment on whether it would help or not. I tend to stick with the less is more approach, especially as one nears the finish line. Good luck.

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No not doing anything drastic here. Just trying to figure out how to dial in and fine tune things. I'm just going to cut back on the Mg and leave it at that and see from there. Thanks again for the advice.

I don't think it looks like light burn. It could be PH fluctuations. I run drain to waste coco and if I saw a PH of 6.5 I would call it good, but I'm no pro and I haven't checked mine in 7 months. I wonder if your feedings at a PH of 5.5 could have caused the issue and some plants prefer a different PH range.

Hey. I had considered this as well and there's definitely some pH related burn on the plant, but it happened about 3 weeks ago when my pH meter went out of wack for a few days which let the medium pH wander above 7 pretty quickly before i noticed. Thats why I was watering so low at times, to get it back into range. The newer damage I'm looking at is entirely on the top of the plant, but ya the pH swing probably has contributed to this issue.