HELP! Yellowing tips on my autoflower, starting from the top

[azorahai]

This is a Magnum autoflowering strain, about a month old and [unfortunately] already in its flowering period. It's been yellowing at the tips, starting from the top, for about a week. I raised the lights a few days ago to rule out light stress, and kept feeding it all the necessary micronutrients and secondary macronutrients, while decreasing nitrogen and increasing phosphorus to promote bud growth. Everything was pH'd to around 5.5, though it was previously being watered/fertilized with a slightly higher pH of about 6. Slurry test (topsoil) showed that the substrate is sitting at around pH 6.3.

Setup: 180W LED lights, peat moss + perlite + vermiculite substrate, watered/fertilized until about 10% run-off, which is checked for salt build-up and pH regularly. The current fert mix was measured at around 1400 ppm, with 06-18-12 NPK, dolomite lime (Mg, Ca) and the remaining necessary micronutrients.

If my research is correct, assuming this is a nutrient issue, this could only be a problem with the immobile nutrients (Ca, S, Zn, Mn, Fe, B, Cu), seeing as it manifested itself first in the newer growth. It doesn't seem like it's calcium deficiency, and I'm pretty sure I'm actually feeding a lot more micronutrients than most other growers. Perhaps it's some sort of micronutrient toxicity? I think it's unlikely, seeing as I use the same concentration of micronutrients in my other non-autos, which have shown no such problems. But then again, they aren't flowering yet.

Any ideas? Thank you!

 

[MeEasy]

I think it looks like wind burn. Do you have a fan blowing directly on it?

 

[lalaland]

It looks like classic light burn to me. I have a new type of light that I’m pushing to the limit, and I keep burning the tips as well.
if your temp is a little high, or your RH a little low as well, this will make it worse

 

[PRIMO]

I'd give em a good flush with pH'ed water. Last gal. 1/2 str. flowering neuts. with a shot of cal-mag.

 

[azorahai]

I think it looks like wind burn. Do you have a fan blowing directly on it?

Yes, but it's a fairly small USB fan like this one, it can barely even sway the plant. Also, the non-autos are also under another one of these small fans. Either way, I'll try to direct the wind elsewhere to see if that helps. Thanks!

It looks like classic light burn to me. I have a new type of light that I’m pushing to the limit, and I keep burning the tips as well.
if your temp is a little high, or your RH a little low as well, this will make it worse

As far as the temperature and humidity go, everything seems to be within tolerance, with max temps at around 30 ºC. I haven't been checking the RH, but it's been raining/drizzling a lot lately so the air is far from being dry.

The 180W LED lamp was 30 cm (~12 in) from the top and 45 cm (~18 in) from the bottom of the plant, and was raised another 15 cm (~6 in) a few days ago, but the discoloring continued. Even the newer growth below has begun yellowing as of yesterday.

I'd give em a good flush with pH'ed water. Last gal. 1/2 str. flowering neuts. with a shot of cal-mag.

I lightly flushed it a few days ago, just to be safe. Before that I was feeding it 1/2 str. vegetative nutes (20-05-20 NPK) that I was using to feed the other plants (they had about a couple of weeks head start). The run-off registered a fairly low ppm (which was expected, seeing as how I wasn't feeding it much), and it didn't improve after a couple of days, so I began feeding it a low dose of flowering nutes (06-18-12 NPK), which I've increased yesterday in the hope of solving this mystery.

 

[lalaland]

I have a couple of cheap160 watt LEDs (100 watt equivalent advertised) that I have to keep A minimum of 28 inches from the top of my plants. That pic I posted was burnt at 26 inches.
Just my opinion, take it for what it’s worth 👍

 

[lalaland]

1000 watt equivalent, not 100, scuse my fat fingers

 

[azorahai]

My LED is also advertised as 1000W equivalent (180w in reality). I'll raise it some more, perhaps this was the issue all along. Thank you!

 

[YYCannabis]

Auto flower that is already flowering...to me looks like potassium deficiency. Very mild case and explains why you aren’t seeing it in the other non-auto plants. Some autos get very hungry for potassium early in flower.
https://www.growweedeasy.com/cannabis-plant-problems/potassium-deficiency

 

[azorahai]

Auto flower that is already flowering...to me looks like potassium deficiency. Very mild case and explains why you aren’t seeing it in the other non-auto plants. Some autos get very hungry for potassium early in flower.
https://www.growweedeasy.com/cannabi...ium-deficiency

Wouldn't a potassium deficiency first manifest itself in the older growth/lower leaves? If I understand this correctly, problems with mobile nutrients (N, P, K, Mg, Mo) show up first in the older growth — as the newer growth is prioritized and nutrients are transferred up —, while problems with immobile nutrients (Ca, S, Zn, Mn, Fe, B, Cu) show up first in the newer growth — as the newer growth can't get sufficient nutrients from the substrate nor can they steal it from the older growth.

Either way, I've since upped the potassium dosage somewhat, and it's been a few days already and the yellowing problem continued spreading downward. I'm thinking it's probably something with the lights, as lalaland mentioned. I'll return with an update soon. Thanks!

 

[YYCannabis]

From looking at your pics, you already have it on lower growth. From the article i posted earlier, they do mention that it can also be a problem with new growth and not just old growth.

Hopefully it resolves quickly for her 👍

 

[azorahai]

Update: it appears it really was a problem with the height of the LED lights. Moved it to about 60 cm (~24 in) from the top of the plant, and haven't noticed any more yellowing. Thank you for you help!

 

[lalaland]

Thought I should add another tidbit About cheap LEDs. I’m a little over halfway through flower, and noticed that the autos will tolerate the light being closer at this point. Same on my last round of photos. I’m at about 20-22 inches now with no burn. Good luck! Hope it clears up for you😁

 

[azorahai]

That's good to know, since my grow space is rather limited. Thanks!