Disease or Humidity

History. New Room.

size 35 ft/L x 15ft/w x 12ft/h

Lights 15 X1000watt hps, 3 led fixtures about 4ft by 4ft.

Grow medium, Coco and vermiculite mix. Bucket size 4gallon. Top feed run to waste, run -off about 10 to 20%

Ferts, Yara and House and garden. Additional, have four rooms running, none of the other rooms have this issue.

First crop in this room showed no issues until about 2 to 3weeks in flower, then it spread from the back of the room to the front. The plants then all looks like they were covered in rust as it spread till harvest.

The second crop had a humidity issue in vege, dropped to about 30%, Repaired that, the once again have the same issue as before happening.

Thoughts… Humidity too low in veg, Calcium or potassium deficiency. As I’m using the same fertilizers in other rooms it’s hard to believe that.

Also, when humidity was low I moved two plants to another room and within 24hrs they were fine and are still fine in the room.

Actions, Have flushed, added Calcinet Nitrate. Checked pots run-off EC and PH. All seems ok.

Thinking there is an environmental issue. Perhaps a fungus or negative-positive pressure?

General observations.

This is the second crop in this room.

Also, I noticed this begin on the top larger leaves.

Interesting. At first glance I thought it may be ‘rust’ sports. If this is the case you are may have some hiddin pathogen fungus spores somewhere in that room. Once your harvest is done do a deep clean of everything.
I would also think about adding some Bokashi, or something of the sort, to add to your soil blend. It works kinda like little piece to a puzzle. Allowing everything to flow and connect with one another.
Look at your magnesium and calcium. This may also cause this look.

The curling of the outer edges makes me think it has been to warm in the room.

Remember these are simply my observations.
Happy growing…


What kind of lights are you using and how close to the plantd are they? How much heat are they emitting? I usually put my hand under the lights to feel the heat. If it’s too hot I point the fan to disperse heat.


HPS lights emit a ton of heat, especially at a 1000 watts


I’ve checked Ca and Mg. They have had a good feed all last week after a flush. Have never used Bokashi. But use fulvic , humic and seaweeds.

Will run some 20% vinegar over the services tomorrow.

This is really weird.

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HPs 1000 DEs and 3 LED 1000 watt fixtures which are about 3ft from the top of the canopy and the 1000’s are about 2ft from the top of the canopy.

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Have an aircon, plus plenty of air coming in through 3 locations with a manifold at one end of the room. Extraction is 250 Whisper fan at about 4.5m height, Temps seem ok, but can get to 90 f. I have the ability to drop that down easy. Today humidity was 50% at 80 f . So I’m confused here.

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Yeah , We are going to slowly change to Fohse A3i’s going forward.

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I grow outside and use LEDs at night for longer veg time. I’ve had times when my leaves got burned, like yours, except I was using 600 watt LEDs. I’ve also had temperatures go as high as 112 degrees with no issues, even with humidity being 70% at night. The solution I found was more air flow, water had to be at 60 degrees and the lights raised higher.
Sometimes, before the plant gets crispy from light burn, they turn dark green.

I forgot to mention that if you foliar spray the plants, be careful. I’ve had the experience of foliar spraying nutes or insecticide with the LED lights on or around noon when the heat from the sun gets going. Big mistake!!! And you’re using HPS, so be careful.

Both good points.

If i crank the air intakes up I then drop the humidity. Low humidity was an issue in veg. So am unsure about doing that. Currently its 50%.

I have done a few foliar sprays. Need to think about that more. Am well aware of spraying midday etc. So would never do that, either early morning or about 1hr before the lights go out.

Plan for tomorrow will be to make another 200L of calmag, lift the lights higher or turn them down. I’ll take some pics of the room so readers can get a better perspective. Its actually got me buggered.

Might be this. Septoria lycopersici

Septoria lycopersici Septoria leaf spot caused by Septoria lycopersici is one of the most destructive diseases of tomato foliage . It is widely distributed throughout the world and is most severe where wet, humid weather periods persist for extended periods.

So u have the hos at 2 ft above and the LEDs are 3 ft above. To me this should be the opposite as the hos throw off 1000 times more heat than a led light does unless they r the cool tube kind. To me u saying it’s the top leaves basically sounds to me like the lights need to be raised up some not the LEDs. Ut the hos lights. U need to get the phone app and get the dli in check u can prolly have the hos lights like 4 feet above the canopy or noreo. Full tilt. @Hoppiefrog might be able to lead u how far away to keep the lamps he grows some killer trees inside lol. Check him out
Well if u click the blue and it’ll take u there don’t know why it only says and lol


I thought about septoria, but it’s usually blotches of brown spots. Doesn’t seem to be that in your case. Just to be sure get rid of the leaves or wipe them down with a 1:10 mix of hydrogen peroxide:water. The soil may be infected, too, but honestly, it’s gotta be the heat. I’ve had septoria and that doesn’t look like septoria. Septoria and light burn are manageable.

Some argue that cal-mag is unnecessary during flowering

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The reason I’m thinking Septoria is the way it is spreading. From the back right of the room through the room.

But check it out today closer and sort the lights out. Take some pcs.

Appreciate everyone’s comments.

Plants under LEDs use a lot more calmag. Here’s some ratio’s to making your own Calmag.

Calmag mix…

Calcium Nitrate -446gms

Mgs -319 gms

Iron chelates 200 gms

Mix separately, then together.

2.5mls p/L or 5/6 MLS p/g

Just throwing this out there: The initial symptoms of a phosphorus deficiency are darkening foliage and slowing growth. The leaves’ edges on your cannabis plant will lose their vibrant green color – they may even turn brown – and will start to curl in.

…but my bet is heat.

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I just noticed major canoeing of the upper / newer leaves. I raised my LEDs a couple inches, and trying to increase humidity in the closet. RH was below 40%, temps usually upper 70’s. However closed the closet door to keep humidity in but temps climbed to 80 at canopy. Opened door.

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