Top Half of Budding Plants Discoloration

[Zootown68]

-Problem: @Mañ'O'Green Top half of my Mephisto CDLC x GW Plants have gotten a lot lighter since some light defoliation while the bottom half's color has not changed. A couple spots are especially weird.... HOWEVER... my Meph Canna Cheese is doing great except for some burnt tips. All of the gals have gotten fed the same stuff/ freq and had the same little haircut to uncover budding sites four days ago. Thank you all for your help in this amazing community!
-Medium/grow method: Royal Gold Tupur straight from the bag.
-Feed and supplements used: GH Flora Trio and all the trimmings. Following GH Drain to waste feed schedule to a T but also adding tiny bit of Yucca powder (like a teense on the end of a knife). Presently putting in 375ppm and watering 3x / day via hand watering to 20% runoff.
-Water source: RO Water pH'd to fluctuate btw 5.75 and 6.0
-Strain and age: Mephisto CDLC x GW at 48 Days
-Climate: 18/6 light sch. Day temps 65 to 70 @ 45% humidity. Night temps 65 to 70 @ 45% humidity. 6" fan and carbon filter running 24/7. Small fan pointing down over lights and one betweenish plants blowing away towards radiator. Tiny dehumidifier not good for much anything.
- Light used: 2 x Viparspectra XS 1500 LED's. 150 watts each. Lights are 14" from high point on each plant running at 100%
-Additional info: Problem started a few days ago after some light defoliation.

Link to my grow journal: https://www.autoflower.org/threads/zootown68s-first-grow-all-mephisto-ladies.81609/

Link to my grow journal: https://www.autoflower.org/threads/zootown68s-first-grow-all-mephisto-ladies.81609/

 

[Mañ'O'Green]

Looks like a micros and cal - mag deficiency. Add some Kelp and humic acid along with 75 PPM of cal-mag to your regular fertigation.

If you have it available a foliar of 5 parts humic acid to 2 parts fulvic acid. Or a foliar application of Earth Juice Micro Blast.

Your daytime temps are on the low side 78°F would be better if you can get it up some.

 

[low_and_slow]

You can get more micros into the plant by adjusting your GH ratios a bit. What's your current feed formula between veg/micro/grow?

 

[Zootown68]

Thanks @Mañ'O'Green and @low_and_slow . I actually have the Microblast from a previous foliar, so will use that again. Will the reg 2.5 ml of Diamond Nectar that goes into the reg feed schedule suffice for the Humic Acid, or do I still need to add more to that for the foliar portion? Thank you.

 

[low_and_slow]

I'm not sure about Diamond Nectar, I just use the base GH 3-part. One other thing I'm noticing is that the lightening looks like it might be from the lights being close...that sort of blotchy white pattern seems like it's more related to the light than something that's wrong in the root zone. Before you add any additives to the root zone, I'd consider your leaf temperatures. If your room temps are in the 60's, you're probably not in the ideal part of the vapor-pressure-deficit curve for that much light intensity, so what could be happening is an acute Mg deficiency only in those parts of the leaves that are most proximal to your light source, which is robust and close given your first post.

My point is that treating this issue in the root zone might do nothing, or create a further imbalance. Something about really high levels of light with low leaf temperatures seems to cause this bleaching effect closest to the lights, and it seems like it's become more prevalent with LED that don't throw off the huge amount of warmth that HID lights like HPS do.

There's a grower on another forum that has an absolute NASA-like grow setup, and he swears by 65%+ humidity and 82* F leaf temps. That sometimes means running a room around 85* since the leaves often get a ton of air movement from circulating fans in a controlled setup. The idea here is that with 82-83*F leaf temps, the plants are able to metabolize everything from the root zone more appropriately in that high-intensity lighting zone. If you go down into the 60's, certain processes shut down that then create the deficiencies you're seeing. Given that your plants appear very healthy outside that max-intensity light cone area, I'd suggest pursuing a more idealized environment before increasing the concentration of fertilizers added to the roots.

This is really tricky for small setups, and can get complicated fast.

Personally, I struggle with this mightily. My environment is crazy arid, so I run a humidifier outside my tent 24/7 and keep my house about 3* warmer on the thermostat than I would prefer, and that still doesn't really address the issue when the lights go off. I try to aim for 78-82*F and 65% humidity, but right now my flowering cabinet runs about 65* lights off, sometimes single-digit humidity levels. That creates its own set of problems, and if you look at my blog entries, you can see the effects of that in the leaf discoloration. I will also say, finishing flowers in cold, super-dry environments seems to create some of the frostiest, most potent weed I've ever seen, like, it's insane. It also cuts my yields by like 30-40%, so I really need to come up with a solution.

 

[Zootown68]

Thanks, @low_and_slow . For some reason I was under the impression that ideal day temps were like 70 in this stage. I can easily get temps to 78 during the day. Thanks, @Mañ'O'Green. I just did the foliar at lights out this morning, so I'll let that marinate in conjunction with the raised temps first, and then give the extra Cal-Mag if I don't see a marked improvement over the next couple days.

I honestly thought that it might be too much light intensity and was ready to back it off and call it good, but sounds like the issue might be a combo of things, like I've seen that it so often is on this forum.

 

[low_and_slow]

Assuming you have no pathogens, you want 78-82 throughout the grow, ideally 50-70% RH.

https://cdn.sanity.io/images/0vv8moc6/cnst/956f75d9cd87f8839d4dc5c14f15c42c98ca0a57-1912x630.jpg?auto=format

 

[Zootown68]

I've been manipulating the temps and RH to a range that doesn't suit the weeds. Damn. Learning. I've still got some time in this grow. I'll see how they pan out. Thanks, all. On the bright side I'll be able to house watch at a diff location with my honey (here in town) and not be so stressed about keeping the plants in the (wrong) environmental conditions.

 

[Mañ'O'Green]

Thanks @Mañ'O'Green and @low_and_slow . I actually have the Microblast from a previous foliar, so will use that again. Will the reg 2.5 ml of Diamond Nectar that goes into the reg feed schedule suffice for the Humic Acid, or do I still need to add more to that for the foliar portion? Thank you.

The study done by the University of Virginia provides that 5 parts humic acid to 2 parts Kelp works 50% better than either product alone.

 

[Zootown68]

That's some far out cats in VA....