Help Identifying Black Spot Cause

[demman]

Hi Everyone, first time grower.

Started seeing these black spots when I watered my plants on Saturday, and they've slowly gotten worse. They started off with just the black spots, but as seen in the first picture, they've developed a lighter green/yellow on the outside of the marks now too. This started about two weeks after switching to flowering, and is only happening on one of my two plants. From what I've found of the posts with similar pictures, people seem to be suggesting calcium/manganese deficiency. I'm new to this, and was hoping to get a second opinion. Any help would be appreciated.

Copied this from the readme on the front page.
1. Are you growing from seed or clones?
Clones
2. How old are your plants?
About 5 weeks
3. How tall are your plants?
15 inches
4. What size containers are they planted in?
3 gallon pots
5. What is your soil mix?
2/3 Fox Farm Ocean Forest 1/3 Perlite
6. How often do you water and what type of water do you use?
Every 2-3 days, tap water...
7. What is the pH of your water?
Unknown
8. What kind of fertilizer do you use and what is its NPK ratio?
None
9. Do you foliar feed or spray your plants with anything?
No
10. What kind of lights do you use and how many watts combined? (HPS, MH, fluorescent, halogen, incandescent "plant lights")
200w LED
11. How close are your lights to the plants?
14 inches
12. What size is your grow space in square feet?
4 ft2
13. What is the temperature and humidity in your grow space?
Keep room around 67, unknown humidity
14. What is the pH of the soil?
unknown
15. Have you noticed any insect activity in your grow space?
Been trying to deal with fungus gnats using mosquito dunks, but not much progress
16. How much experience do you have growing?
First time grower

 

[Sh311Sh0ck3d]

Hey. First thing everyone will tell you is you really need to know what the ph of your water is. You really need to read up on that.
That might be nutrient burn from the nutrients in the soil. But without knowing where any of your ph levels are at, it could be as simple as that. I wouldn't worry about it too much just read up on best ph for cannabis, probably around 6.2 but anywhere between 6 and 6.5 is good. Add a table spoon of epsom salts to a gallon of water for next time you water them. Just back of the watering and let the soil dry out, obviously don't leave it too long. Magnesium deficiency usually shows with yellowing of the leaves, its obvious and your plants look fine. Similar to nitrogen deficiency. Don't over do it with the Epsom salts either. Less is more when it comes to plant foods. Its always easier to add more, its very difficult and stressful to the plants when you over do it.
Download a copy of the Cannabis Growers Bible by Greg Green. You can get a pdf free, its like part of the grow room tool kit.

 

[demman]

Hey. First thing everyone will tell you is you really need to know what the ph of your water is. You really need to read up on that.
That might be nutrient burn from the nutrients in the soil. But without knowing where any of your ph levels are at, it could be as simple as that. I wouldn't worry about it too much just read up on best ph for cannabis, probably around 6.2 but anywhere between 6 and 6.5 is good. Add a table spoon of epsom salts to a gallon of water for next time you water them. Just back of the watering and let the soil dry out, obviously don't leave it too long. Magnesium deficiency usually shows with yellowing of the leaves, its obvious and your plants look fine. Similar to nitrogen deficiency. Don't over do it with the Epsom salts either. Less is more when it comes to plant foods. Its always easier to add more, its very difficult and stressful to the plants when you over do it.
Download a copy of the Cannabis Growers Bible by Greg Green. You can get a pdf free, its like part of the grow room tool kit.

Was finally able to get a ph meter, yikes. Water is testing at mid 7.3s out of the faucet. Not sure why this didn't affect the plants until a month into the grow, but I recently started watering them with a larger amount. Maybe that was the tipping point the plant could handle.

The plant has continued to suffer the past couples days, but hopefully this was caught in time. Thank you for the help.

 

[Beachwalker]

Need a picture of those spots in daylight without the purple tint

..also what's your humidity like? (You answered unknown above so I'm guessing that you don't have it controlled, you don't have a hygrometer and your humidity is whatever the ambient is in the tent, so likely high, at least at times)

How much air movement / fans do you have?

It's likely one of two things, but without a daylight picture I'm hesitant to say

 

[Sh311Sh0ck3d]

Was finally able to get a ph meter, yikes. Water is testing at mid 7.3s out of the faucet. Not sure why this didn't affect the plants until a month into the grow, but I recently started watering them with a larger amount. Maybe that was the tipping point the plant could handle.

The plant has continued to suffer the past couples days, but hopefully this was caught in time. Thank you for the help.

No worries. I cannot be certain ph is the cause but anything over 7 is high. 6.2 is perfect but between 6 and 6.5 will do. Any additives you add to the water, fertilizer will affect the ph, and it can change. Most bought soil is 6 but it usually says on the bag and I am sure there are different soil mixes so the soil I buy is 6. Don't waste money on a soil ph kit unless you are getting soil from the yard. Don't get soil from the yard! For all soil costs its worth spending whatever. I pay £18 British pounds for a 50 litre bag of All mix. I buy worm castings and mix some into the soil and make " worm tea" with it.
Its seems odd one plant is affected and the other isn't.
I see Beachwalker has posted as well. I am sure if you provide the photo's and other information he ask for he will be able to provide you with some answers. Very helpful community here.

 

[demman]

Need a picture of those spots in daylight without the purple tint

..also what's your humidity like? (You answered unknown above so I'm guessing that you don't have it controlled, you don't have a hygrometer and your humidity is whatever the ambient is in the tent, so likely high, at least at times)

How much air movement / fans do you have?

It's likely one of two things, but without a daylight picture I'm hesitant to say

Sorry haven't checked here since I posted that last update. I've attached some photos with the lights off, hope that helps. The first two are from the plant that first had spots appear, the last is from my other plant that has began to show symptoms as well.

Still haven't purchased any climate monitoring so humidity is an unknown. I've never opened my tent and felt it was muggy on the inside. Seems about the same as whatever is outside. I have an inline fan leading to a filter to serve all my air pushing needs. I keep a few slots opened a crack on the tent (2x2x5) to support airflow.

The plant that originally started getting the spots has seemed to plateaued at a state of most of the older fan leaves having spots. The younger growth seems to be surviving for now though. The spots also have began to appear of leaves of my other plant, but does not seem to be spreading nearly as fast as it did on the first plant. Hoping the adjusted ph water and added calmag will slowly save the day.

 

[Beachwalker]

So I want you to look up leaf septoria; here is a couple of pictures to give you an idea what I believe you've got going on, it's a fungus caused by high humidity and low air flow. Recommend you read up on it

When I first started growing again five years ago I dealt with & stopped septoria, heres two specific recommendations:
Increase low airflow, and search 'liquid copper fungicide', best wishes and feel free to tag me in if I can help further

Edit: Alternaria is a new one on me and I'm going to be reading up on it later this morning, but it's treatment is likely the same as for the more classic septoria

 

[Beachwalker]

Edit to add: Mix one level tablespoon of baking soda to 1 gallon of water, spray both sides of the Leaves to stop it instantly, but must be repeated almost daily

A better and longer-lasting treatment is liquid copper fungicide which is what I use. Some also use a product called wettable sulfur but I've never used it & know nothing about it

 

[Milson]

Edit to add: Mix one level tablespoon of baking soda to 1 gallon of water, spray both sides of the Leaves to stop it instantly, but must be repeated almost daily

A better and longer-lasting treatment is liquid copper fungicide which is what I use. Some also use a product called wettable sulfur but I've never used it & know nothing about it

Wettable sulfur smells awful but sure does work for mold and mildew. I have had success with it on my wife's tropical plants.

I also wonder if this infection (my guess is @Beachwalker is right) may have come in part from weakness due to running low on K. I might also take a look at adding a bloom nute....five weeks with just ocean forest and 1/3 perlite and stress during the stretch makes me wonder...I would check pH first as course as it's often present but not available due to salts and pH...

 

[Beachwalker]

Wettable sulfur smells awful but sure does work for mold and mildew. I have had success with it on my wife's tropical plants.

I also wonder if this infection (my guess is @Beachwalker is right) may have come in part from weakness due to running low on K. I might also take a look at adding a bloom nute....five weeks with just ocean forest and 1/3 perlite and stress during the stretch makes me wonder...I would check pH first as course as it's often present but not available due to salts and pH...

I've run certain strains for months without feeding Ocean Forest; op's plants look plenty green, what I've found from my own experience is that fungus is caused by crowded plants, low air movement, high humidity &/or big humidity fluctuations

However from my investigation on septoria I agree that plants showing these issues should be fed more aggressively than they might be ordinarily, and I always feed plants when they go into bloom regardless

Regarding sulfur I'm only familiar with sulfur burning which is what I continued after the liquid copper fungicide treatments and it helped eliminated septoria, however you have to be ever vigilant against it!

 

[Flexnerb]

Sorry haven't checked here since I posted that last update. I've attached some photos with the lights off, hope that helps. The first two are from the plant that first had spots appear, the last is from my other plant that has began to show symptoms as well.

Still haven't purchased any climate monitoring so humidity is an unknown. I've never opened my tent and felt it was muggy on the inside. Seems about the same as whatever is outside. I have an inline fan leading to a filter to serve all my air pushing needs. I keep a few slots opened a crack on the tent (2x2x5) to support airflow.

The plant that originally started getting the spots has seemed to plateaued at a state of most of the older fan leaves having spots. The younger growth seems to be surviving for now though. The spots also have began to appear of leaves of my other plant, but does not seem to be spreading nearly as fast as it did on the first plant. Hoping the adjusted ph water and added calmag will slowly save the day.

Just read lil bout this on alchimia. Beach is right. @Beachwalker if i remember i had a disagreement with your opinion to a members leaf septoria issue. I said what i said long story short i had it backwards. It was leaf sep and i believe this is the other disease i was suggesting. I remember reading about it some 4 or so years ago..

Back to the OP! Hey bud, ill post you up the link.

Edit

Alternaria in the cannabis crop

In this post we will explain you about Alternaria, a pathogenic fungi that affects both people as to a large number of plants and agricultural crops. To know what it is, how it propagates itself and what you can do to prevent or control its appearance will be of great help to keep this fungus...

www.alchimiaweb.com

 

[Milson]

I've run certain strains for months without feeding Ocean Forest; op's plants look plenty green, what I've found from my own experience is that fungus is caused by crowded plants, low air movement, high humidity &/or big humidity fluctuations

However from my investigation on septoria I agree that plants showing these issues should be fed more aggressively than they might be ordinarily, and I always feed plants when they go into bloom regardless

Regarding sulfur I'm only familiar with sulfur burning which is what I continued after the liquid copper fungicide treatments and it helped eliminated septoria, however you have to be ever vigilant against it!

This is reasoning behind my guess. I just dealt with a potassium deficiency recently at a similar stage using ocean forest so i thought it might be partially operative. From Cervantes.

Again, I think you're right. Just that this might also be contributing and merits investigation.

 

[Flexnerb]

This is reasoning behind my guess. I just dealt with a potassium deficiency recently at a similar stage using ocean forest so i thought it might be partially operative. From Cervantes.

Again, I think you're right. Just that this might also be contributing and merits investigation.

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Im sure it has a lot to do with K keeping the gaurd cell happy

 

[Milson]

Im sure it has a lot to do with K keeping the gaurd cell happy

I agree with that thought and I bet the spots in the leaves are just begging for an infection if the deficiency progresses. Again idk if it's operative here. Just saying "maybe, here is my thought and source on why."

 

[demman]

Any suggestions on the best nutrient mix to get for this problem? Go for one with a higher k value or stick with a general bloom?

Is the copper fungicide worth the investment over the baking soda mix? Figure I'll try to hit all these points today, thank you for all the advice everyone.

 

[Beachwalker]

B

Any suggestions on the best nutrient mix to get for this problem? Go for one with a higher k value or stick with a general bloom?

Is the copper fungicide worth the investment over the baking soda mix? Figure I'll try to hit all these points today, thank you for all the advice everyone.

Nutrients have nothing to do with why your plants have fungus, I left you a list of causes above

Regarding baking soda if you want to spray it everyday with marginal results have at it; if you want to possibly cure the problem buy the copper fungicide

I guarantee you the problem you have is severe and it will affect every plant before long, good luck.

 

[demman]

B

Nutrients have nothing to do with why your plants have fungus, I left you a list of causes above

Regarding baking soda if you want to spray it everyday with marginal results have at it; if you want to possibly cure the problem buy the copper fungicide

I guarantee you the problem you have is severe and it will affect every plant before long, good luck.

Should I be worried about residual copper in the buds? Been looking at past threads talking about it on these forums, but can't pick out a general consensus. Regardless, just got back with the spray, hopefully this will be the last step.

 

[Flexnerb]

Copper im thinking is a last resort when organics fail

Should I be worried about residual copper in the buds? Been looking at past threads talking about it on these forums, but can't pick out a general consensus. Regardless, just got back with the spray, hopefully this will be the last step.

 

[Milson]

Should I be worried about residual copper in the buds? Been looking at past threads talking about it on these forums, but can't pick out a general consensus. Regardless, just got back with the spray, hopefully this will be the last step.

I think you are early enough to be okay. Just use it thoroughly now and get that air flowing with a fan etc would be my recommendation.

 

[Milson]

Any suggestions on the best nutrient mix to get for this problem? Go for one with a higher k value or stick with a general bloom?

Is the copper fungicide worth the investment over the baking soda mix? Figure I'll try to hit all these points today, thank you for all the advice everyone.

Just get a standard bloom nute. You are not going to fix this problem with nutes but they should be part of your regimen going forward to the end of the grow and I think an imbalance or deficiency may have contributed to the conditions that allowed this fungal infection to take hold. You are losing a lot of leaf mass though so you need to kill this fungus first and worry about the aftermath after that! This is like losing solar panels if you get what I mean and it could go beyond that. Hopefully the copper does the business. Make sure to get lots of air moving and keep humidity down!

Again, you also want to check out pH.