Deep purple/red dots turn into necrosis. What is this?

[The_Moz4rt]

My second post here, first time grower running an autoflower in DWC. Day 65 from sprout, 3-4 weeks into flowering and I guess something like 4 weeks before harvest.
I'm currently fixing a nutrient burn, but for the second time (after about two weeks) I see these deep red/purple dots spreading (colour looks like blood or hydro A solution, while it's not). They turn into necrosis after a couple of days. It's not a pH issue!
I'm confident this second wave of dots popped up today. I'm using the usual mix, actually lowered to 1.4 EC (mS/cm) from the previous 1.55. While she's drinking tons of water, the nutrient uptake slowed down, hence a lower EC.
Using Canna Aqua Flores A+B and CalMag from Atami.

Here some pics of the dots right now:

Here is how old dots like those became:

Any idea of what this could be? Nute burn? Deficiency? Fungus?
I'm now cleaning everything again inside the grow box. I'm going to lower the temps from 28°C to 25. As well as decreasing RH from 60% to 45ish.

 

[lemonade]

Hmmm perhaps it could be fungal? Specifically "rust", i.e Pucciniales. I could be wrong.

I used to use a fungicide called Manzate for it. I believe it was 1 gram per gallon though don't quote me on that. Used in veg only of course, or on moms etc so that wont help you unfortunately

I think Nova 40w kills rust also; although again veg only. :-(

 

[flylowgethigh]

What does the bottom of the leaf look like? Could it be bugs? Fix with scissors by cutting off and discarding the affected leaves?

Nice frost.

 

[BorpotChrist]

https://content.ces.ncsu.edu/strawberry-potassium-k-deficiency

 

[The_Moz4rt]

Thanks guys. I was worried as well it could be a fungus, especially since I was running high temps and RH to stay in a good VPD zone.
Upon further thought tough, I'm wondering if it could be due to a sort of flush I did yesterday while I was changing and cleaning the reservior.

I left the plant 10 min in pH'd tap water only. And before this, pH of old solution was 5.5
So maybe I pH jump, or she didn't like the pure tap water (0.4 EC).

I moved the light a little bit up, working on temperatures/rh and trying to keep a steady pH. I'll update if no more symptoms show up.

 

[Creeperpark]

Those are tap water spots on the leaves. Tap water will cause this because the water impurities block receptors and get stored in the leaf tissue. It's best to keep the water consistent without any changes because the plant's chemistry is already programed or dialed in. Any changes to soil or water that the plant is not used to will cause disruption of one kind or another. Tap water has a lot of bad hydroxyls and will override the good stuff.

 

[Creeperpark]

Large water treatment programs are designed to eliminate the cation exchange capacity in water so it doesn't leach metals from old water pipes. It's designed to block and lockout any kind of moble nutrient from being transported in the water. Water systems raise the pH to 11 using a chemical called sodium hypochlorite and keep it there until its ready for transport. The high pH will kill or immobilize the bad stuff that's already in the water. When it is transported the pH is dropped using sodium bisulfite with a pH of 3.6! All those sodium molecules from the two chemicals raise the hydroxyl content to a high range. When tap water is used that stuff has to go somewhere and ends up in the soil and leaves.

 

[blondie]

I’m going to cast a vote for over nuted. The tips of a bunch of your leaves have nute burn in my opinion.

 

[TanzanianMagic]

My second post here, first time grower running an autoflower in DWC. Day 65 from sprout, 3-4 weeks into flowering and I guess something like 4 weeks before harvest.
I'm currently fixing a nutrient burn, but for the second time (after about two weeks) I see these deep red/purple dots spreading (colour looks like blood or hydro A solution, while it's not). They turn into necrosis after a couple of days. It's not a pH issue!
I'm confident this second wave of dots popped up today. I'm using the usual mix, actually lowered to 1.4 EC (mS/cm) from the previous 1.55. While she's drinking tons of water, the nutrient uptake slowed down, hence a lower EC.
Using Canna Aqua Flores A+B and CalMag from Atami.

Here some pics of the dots right now:






Here is how old dots like those became:






Any idea of what this could be? Nute burn? Deficiency? Fungus?
I'm now cleaning everything again inside the grow box. I'm going to lower the temps from 28°C to 25. As well as decreasing RH from 60% to 45ish.

Boron deficiency/lockout is likely. The damage starts at the top of the plant (non-mobile nutrients, so not NPK,Mg), and starts at the middle of the leaves.

Boron deficieny is caused by dry air or low pH.

https://www.bonzaseeds.com/blog/boro...nt-prevention/

UPDATE

Additionally, it could also be leaf septorium, which occurs at higher humidities. It made me think of boron because of the damage on the higher leaves.

However if you look at the parched spots, some with yellow edges around them, it could be septoria.

"Disease symptoms begin in lower leaves and within the inner canopy where leaf wetness and high humidity occur. Disease begins as small irregularly shaped spots with bright yellow margins. Spots expand to about ¼ inch in diameter and appear brown with a prominent yellow halo.

As spots enlarge, brown areas become more irregular and develop gray to white centers. Yellow halos expand outward from spots. Advanced symptoms include coalescence of yellow areas and/or coalescence of brown spots. Entire leaves rapidly become yellow and drop from plants."​

Source: https://agfax.com/2019/08/07/kentucky-hemp-dealing-with-septoria-leaf-spot/

 

[gizmo666]

to me it looks more like rust fungi

 

[Creeperpark]

I'm going through the same thing with 2 plants. I had run out of rainwater because of drought and had to use RO water for 2 waterings. The pH of the new water was way too low and needed to be buffered. So I added 2000ml of tap water to 5 gallons of RO to bring the pH from 5.8 to 6.2. The next morning I noticed these spots. Since then I have got a lot of rain and have my rain barrels full again I have had no more spots. That stuff in tap water has to go somewhere and ends up in the leaves.

 

[Koondense]

Septoria is not so likely, the spots look different when fungus strikes, they start in the canopy not on exposed leaves.
My vote goes to some lockout like boron or maybe even K.
Cheers

 

[St. Phatty]

maybe look up Cannabis Academia, find someone you can send the leaves too.

Heavy metals like Uranium are far more common-place than people are aware.

e.g. most of us got about 90 micrograms of Uranium in our bodies.

That's 90 x 10e-6 grams/ 238 grams per 6 x 10e23 atoms

90 x 6/238 10e23 10e-6

2 x 10e17 Uranium 238 atoms - that's how many Uranium atoms you got in your body, on average.

But you got 37 Trillion cells, 3.7 x 10e13

So about

.54 x 10e4 Uranium atoms per cell, call it 5000 Uranium 238 atoms per cell, with a smattering of U235.


Same in the water & soil.

What happens if one of those atoms gets embedded in a Cannabis leaf ?

I would expect it to cause some localized necrosis, depending on 1/2 life and those rare moments when a Uranium atom gives it all up and splits apart into Xenon & Cesium or whatever.


Though there's probably lots of chemicals that can cause spots of Necrosis.


But overall I think the #1 Culprit is people loving their plants too much & over-nuting them.