Brown rust spots on leaves

I'm struggling to figure out what these brown spots on my leaves could be.




What I did read is possible burn from spraying the leaves with liquid seaweed while under light? Its only on the older leaves and not the new growth (which I haven't sprayed)

If anyone knows what this is & a way to fix that would be really helpful! Thanks

You should always spray with lights off unless you are using a product like foliar from Optic or similar brands that say you can spray with lights on. What medium are you in (looks like coco)? Are you feeding calmag? My guess off the information you've given would be its not getting enough calmag. Coco needs more calmag than what you would think. What is your PH?

I'm using Canna Terra soil think it's a blend of coco perlite and soil. Stupid I know but I haven't been feeding cal mag still waiting for that to arrive... As for pH I don't currently have a meter but I've been using the pH perfect GMB from Advance Nutrients I know this is not ideal I was a bit eager to start the grow and don't have all of the equipment yet.

So you think feeding cal mag and adjusting pH would be a good fix?

OGFrosty said:

I'm using Canna Terra soil think it's a blend of coco perlite and soil. Stupid I know but I haven't been feeding cal mag still waiting for that to arrive... As for pH I don't currently have a meter but I've been using the pH perfect GMB from Advance Nutrients I know this is not ideal I was a bit eager to start the grow and don't have all of the equipment yet.

So you think feeding cal mag and adjusting pH would be a good fix?

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I thought I saw some dried out coco in the pics, but didn't think that it was a combination of coco and soil. I have never used your specific branded medium, but have grown in soil plenty of times. I imagine that since its soil you should stick to a PH between 6.5-7.0. Honestly tap water is generally fine. Definitely add cal mag when you can. If you can go pick up some epson salt from the store while you're waiting and do a foliar feed @ 1.5Grams per gallon you will be fine until your calmag arrives (quick short-term assistance) - assuming that delivery timeframe is within the week or so. You could also sprinkle some dolomite lime around the base of the plant and water it in (longer-term assistance). That will only last for a few weeks at best, so make sure to keep feeding the plant. You're going to need to amend your soil a few weeks following planting, after your soil's nutrients have exhausted, and continue through your plants life.

Thanks man, I'll go and grab some Epsom salts while I wait. Cal mag should be here by Monday so hopefully it won't get much worse.

Good Luck, man! Just remember to spray with lights off and don't worry about PH'ing the foliar spray. However, I personally would add a wetting agent to the foliar mix e.g. a dash of dish soap.

If all we have to go off of are pics of two leaves one would guess it appears you're short on Ca (Calcium)...and while CalMag will work, it's comprised of two elements Ca and Mg. Calcium Nitrate or another derivative would be your best bet to solve a shortage in Ca. For the record Epsom salt only imparts Mg, not Ca. Also, if it were a result of spraying, I would think the spots would be on all the leaves, but I'm not sitting in front of your grow so it's hard to say. Good luck friend.

CannaCountry said:

If all we have to go off of are pics of two leaves one would guess it appears you're short on Ca (Calcium)...and while CalMag will work, it's comprised of two elements Ca and Mg. Calcium Nitrate or another derivative would be your best bet to solve a shortage in Ca. For the record Epsom salt only imparts Mg, not Ca. Also, if it were a result of spraying, I would think the spots would be on all the leaves, but I'm not sitting in front of your grow so it's hard to say. Good luck friend.

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For the record, epsom salt has mag and sulfur.

CannaCountry said:

If all we have to go off of are pics of two leaves one would guess it appears you're short on Ca (Calcium)...and while CalMag will work, it's comprised of two elements Ca and Mg. Calcium Nitrate or another derivative would be your best bet to solve a shortage in Ca. For the record Epsom salt only imparts Mg, not Ca. Also, if it were a result of spraying, I would think the spots would be on all the leaves, but I'm not sitting in front of your grow so it's hard to say. Good luck friend.

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The reason I suspected spraying was because it only seems to be happening on the leaves that were sprayed when the plant was younger, I realised that spraying under light was not ideal later on so I stopped spraying the leaves after the first week or so and the new leaves aren't affected.

I will look into Calcium Nitrate, thanks for the heads up

How is your plan getting on? I'm having the same issue but is not of spraying.

badeadinho said:

How is your plan getting on? I'm having the same issue but is not of spraying.

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My plants have all been chopped now, I think I managed to fix it temporarily by backing off the nutes and adding calmag. Although I couldn't ever get to the bottom of it and it seemed to give me problems every so often during the grow on my two larger plants.

Good to know. Ive had the same thought today of backing off with nutrients and just add some calmag. My Northern Light even though shoes this brown spots, she is growing a lot but I think is her from her genetic. The two Gorilla that I have, they are slowing the same brown spots and are growing slow. Hopefully I will get it sorted soon.