What causes this problem in cannabis plants??? (PICS)

The plants are just 21 days into flower and many of the top leaves are already just lousy with this stuff.

When I grow I have no problems whatsoever in the vegetative stage. The plants are lush, green, thriving no problems.

But every single grow I have done in the last four years when I flip the lights to 12/12, somewhere between day 15 and day 25 of flower this rapidly progressing leaf death starts. When it starts I have found no way to stop it, or indeed even slow it. It's just a quick downward spiral into the bin (they live maybe 10-14 days after it first appears at most...it kills them FAST).

It only effects leaves that are receiving HID light. I have tried both HPS and MH, no difference.

So my questions are:

1. Does anyone know what causes this very unique and destructive pattern of leaf death?

2. If this was your crop, and if you could keep it alive for just another twenty to thirty days you would win some very valuable prize, what would you do, right now and going forward, to make it stop?

The plants are in 3gal soil, 3'6 tall, eight of them in a 8x4 cab, 2x 600W HPS, 80 degrees lights on 75 lights off, RH 40-50%, oscillating fan. Nutes are Jacks Classic 20-20-20 and Flower Fuel 2-34-32. Water is tap. One thing of note I discovered recently is that my nutes have no calcium or magnesium in them, does that even matter since they're only micro nutes?

Any and all replies welcome. Thank you.

PICS:


And this is what they look like once this malady gets finished with them...this was the BEST plant of my last "harvest"...

I suck at diagnosing plants, but to properly help you, people will probably want some pics under natural light. Also, it would probably help if you went into much more specific detail on your feed regimen: mixing ratio, EC, feed frequency, etc.

I am not sure if this is related to your issue- bit that is too much N for flowering-
This is one of the benefits of using the GH 3 part- it can be dialed in to your specific needs during different stages

I doubt you have no micro nutrients or you'd be fucked, you can't grow without micro nutrients, though its possible you might have plenty of calcium and magnesium in your tap water.

I'd guess it's salt build up from improper watering and feeding.
Generally that is when it starts.

I'd flush them and start feeding something more balanced.

Then I'd scrap soil and switch to coco next time, but that's just me

Fangthane said:

I suck at diagnosing plants, but to properly help you, people will probably want some pics under natural light. Also, it would probably help if you went into much more specific detail on your feed regimen: mixing ratio, EC, feed frequency, etc.

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Right now I'm feeding Jacks Classic 20-20-20 3/4 teaspoon per gallon of tap water and 1/4 teaspoon of Flower Fuel 2-34-32. Since the buds have set the transpiration rate has increased dramatically so I'm having to water about every three days. The plants are in 3gal pots. I don't know the EC.

Bud man 43 said:

I am not sure if this is related to your issue- bit that is too much N for flowering-
This is one of the benefits of using the GH 3 part- it can be dialed in to your specific needs during different stages

Click to expand...

Do you mean the plants appear to have too much N in them or the nutes I'm using have too much N?

What is GH 3 part? Is that a nutrient program like the three part Foxfarm nutes?

coreywebster said:

I doubt you have no micro nutrients or you'd be fucked, you can't grow without micro nutrients, though its possible you might have plenty of calcium and magnesium in your tap water.

I'd guess it's salt build up from improper watering and feeding.
Generally that is when it starts.

I'd flush them and start feeding something more balanced.

Then I'd scrap soil and switch to coco next time, but that's just me

Click to expand...

The ingredients on the nutes list all the micro-nutes except magnesium and calcium, so I don't know if they are getting (enough of) those two.

I thought the same thing about salt build up, but doing a flush (3x pot size = 9gal water each) and feed seems to have no effect. In fact I just flushed them four days ago and it seemed to accelerate the damage.

They are for 100% for sure NOT getting enough Calcium, and Magnesium. If youre not adding it with that fertilizer, youre basically teasing the plants with the amount they get.
Most likely why nothing happens in veg is because they are surviving, and going right along not really showing a deficiency, even though they are mostly getting enough to survive, and not show deficiencies.

Then when they really start to flower, thats what breaks the camels back. They need all that calcium, and magnesium now, to form hormones, accelerate physical plant growth, accelerate flower formation. When you make a plant flower, its going to need more of EVERYTHING, Including Nitrogen, in small amounts until the last 2 weeks before harvest, then cut back all fertilizer 25%-50%. Its all a matter of PPM. And I dont try and find the limit on how much fertilizer they can take either. I feed small amounts every watering. Usually 20%-40% of recommended dose. If it would say a Tablespoon per gallon, Id give it a TBSP in 5 gallons water.


IMHO you have a Calcium, and Magnesium problem. Jacks 20-20-20 doesnt have nearly enough Calcium, or Magnesium. But theres nothing wrong with the 20-20-20 ratio, though it could possibly use more Potassium. But back in the late 70s-90s we grew plenty of killer weed with Miracle Grow 20-20-20, and Peters 20-20-20, and used 5-50-17 bloom booster. And back then we used a lot of topsoil, and added both Calcitic, and Dolomitc Lime to the soil, so they got both Calcium, and Magnesium in that way.
Marijuana is an extremely heavy magnesium user, and add to the fact that magnesium deficiency is the #1 container grown deficiency. Magnesium, and calcium both are extremely important.
Flushing your plants is only washing what little Magnesium there is left, and as you said, the plants look worse.

I myself like Calcium Nitrate as my Calcium, and Nitrogen source. Then I add Epsom Salts ( Magnesium Sulfate ) for my Magnesium, and Sulfur.
But if I was to use the 20-20-20 I would simply use Cal/Mag to keep it simple.

I'd say you're getting some lockout from the tap water. The Jack's does bring down your Ph, but not very much. My tap water before filtration has a high seven Ph. From this chart Mg cuts out around seven. You really ought to try some Ph down, after you put all your nutes in.

Switch to coco

jimihendrix1 said:

They are for 100% for sure NOT getting enough Calcium, and Magnesium. If youre not adding it with that fertilizer, youre basically teasing the plants with the amount they get.

[]

IMHO you have a Calcium, and Magnesium problem. Jacks 20-20-20 doesnt have nearly enough Calcium, or Magnesium. But theres nothing wrong with the 20-20-20 ratio, though it could possibly use more Potassium.

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Thank you very much for your helpful, detailed reply jimihendrix1!

I think you may be onto something with the calcium as the soil I used to grow in had this stuff called dolomite lyme (sp?) in it which supposedly has calcium but it's not in the soil I'm using now.

Will this nute pictured below help with a calcium deficiency? I was going to try it last year but someone told me it was only for hydro, will it work in soil?

Anyway, it says to feed 3-5ml per gallon nominally. Would you give it 5ml next watering or would you go higher to correct the deficiency faster?

Thanks again for your help, I really learned a lot from your post...much appreciated.

CAL-MAG:

warble said:

I'd say you're getting some lockout from the tap water. The Jack's does bring down your Ph, but not very much. My tap water before filtration has a high seven Ph. From this chart Mg cuts out around seven. You really ought to try some Ph down, after you put all your nutes in.

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I don't have any ph-down but I do have some white vinegar, which also lowers ph.

My water is ph 7.3 out of the tap. I don't know what it is after adding the Jacks nutes, as I have no way of measuring it.

Can white vinegar be added to the water with nutes in it to bring the ph down, and if so how much do you think I should add per gallon? Or should I just play it safe and order some ph-down?

Thank you.

I've used vinegar, citric acid and they are very temporary. Ph down would be better especially during flower, but what is more important is either get a Ph meter, litmus paper or water tester kits. I have a cheap Ph meter from China and it was less than $10. I've used it for years. You could spend $40 or $150, They'll probably last just as long or longer, but you're getting started. Don't know if you'll wanna keep this hobby going. This set could help:

Id go by the directons, and Cal Mag works in soil.

Day 28 of Flower - Death Marches On

My crop is continuing it's quick rapid march to the graveyard.

Every day it gets worse. I wake up, go into my grow cab, see yet more damage. Every day. It's like having an NFL linebacker tackle me at full speed - a crushing body blow, every day.

A poster above suggested a possible calcium deficiency.

Well on Sunday I fed them the CAL-MAG first time, along with 3/4 teaspoon Jacks 20-20-20 and 1/4 teaspoon Flower Fuel 2-34-32 per gallon of water - no change, no improvement - they just keep dying.

So I guess we can cross calcium / magnesium deficiency off the list of potential causes for this as they've had CAL-MAG for two and a half days now and there's no change or improvement whatsoever.

I'll stop the CAL-MAG going forward, just feed the Jacks Classic and Flower Fuel.

Any other ideas? Anything I can do to salvage at least some semblance of medicine out of this crop? Any ideas on what I can do to NOT have this happen on future crops?

Someone on another forum recommended dolomite lime...I don't even know what that is but they have it on amazon...do you think that would help?

This is literally ruining my life. This current crop failure means I will be in continuous pain until Christmas with no end in sight.

At the suggestion of posters here, I have ordered a pH test kit and some pH-down. It will arrive Friday, but I have never used anything like that before on any kind of plant, let alone cannabis.

I do not suspect a pH problem because last week I flushed with 3x gallons pot size of water, then fed, and it actually made it worse. Isn't doing that supposed to "reset" the pH and flush excess nutes?

Anyway, to quickly summarize the symptoms:

-Plants fine in veg, absolutely no problems whatsoever.
-Plants are fine the first 15-25 days of flower.
-Then I get yellowing, burning and tiny brown "holes" (spots) on fan leaves receiving light.
-Continues until all fan leaves on upper 2/3 of plant are dead, then the bud leaves start dying.
-Can't keep the plants alive longer than ~40-45 days MAX after flower starts. Need 60-90 days.
-Weak stems, weak roots, slow growth, small weak buds, main stem is hollow (!) following harvest.
-No sign of pests, including spider mites.

Any and all replies/suggestions/ideas welcome. Thank you.

PICS (taken today 9/6):

One treatment of Cal/Mag wont cure it. And Calcium, and Magnesium should be available at each feeding. Calcium, and Magnesium, are as important as NPK.
And those damaged leaves are never going to recover.
Plants need a complete nutrient ratio. What do you think would happen if you cut Mg, and Ca out of your diet???

jimihendrix1 said:

One treatment of Cal/Mag wont cure it. And Calcium, and Magnesium should be available at each feeding. Calcium, and Magnesium, are as important as NPK.
And those damaged leaves are never going to recover.
Plants need a complete nutrient ratio.

Click to expand...

So the CAL-MAG needs more time to work?

I guess I was expecting something like when you have a N deficiency, say, then you feed more N and like the next day the plants are noticeably greener and healthier.

So you think I should continue feeding cal-mag at the recommended rate? Will it at least prevent damage to the remaining leaves, and how long does it take to kick in?

Thanks again jimihendrix1. You sound very knowledgeable on this subject, so your counsel is very much appreciated.

jimihendrix1 said:

What do you think would happen if you cut Mg, and Ca out of your diet???

Click to expand...

I didn't know people needed Mg but I think if you cut Ca out of your diet your bones would disintegrate? IDK I'm no doctor. It's a good question though.

1. Cal-Mag is a supplement, not fertilizer, just feed it with every watering unless the fertilizer has cal-mag in it.

2. Two days of cal-mag is not enough time to work. Magnesium deficiencies exist 4-6 weeks before any physical symptoms first appear.

3. Why are you still feeding Jacks fertilizer? It seems like the constant input in this death march is the fertilizer. I would try switching to something complete and easy to use. I like GH Flora Nova, 1 bottle for veg, 1 bottle for flower. Cal-mag and everything else included. Mixed to the correct strength and the ph will be balanced as well.

4. Get a good ph meter and use it every time you water. Ph to between 6.4 and 6.8 in soil.

5. Use good, fresh potting soil, especially to repot before you flip to flower. I repot from 1 to 3 gallon, and flip in a few days.

6. Do not expect to rescue the current death march, the leaves will not recover and it's too late to grow new leaves. Just do the best you can and plan a different regimen for the next grow.

7. Please refer to this chart for more information:

Looks like Phosphorus toxicity.

If you're feeding 3 grams of 20-20-20 and 1 gram of 2-34-32 you're feeding about 110ppm of Phosphorus. Anything over 100ppm of phosphorus is in the toxic range. you might be feeding even more than that, im just guessing that 3/4 of a teaspoon is 3 grams and 1/4 is 1 gram.