Brown spots on the leaves, 37 days 12-12 light, DWC

Mich000 · Jan 10, 2022

Hi everyone,

Im in the 37 days of flowering, and some of the leaves add the top of the plant have some brown spots on them/

Its a DWC setup with just 1 plant in a room of 60x60x180cm , with 150 watt quantum led.

this is what im feeding:
- 12 liters of rainwater
- Plagron hydro A+B ( 18ml of both)
- dutch pro calmag 6ml
- Greensensation 6ml

EC = 1700
PH +/- 6

2 days before the brown spots i had some leave tips burned so i placed my light i bit higher.
But now it shows some brown spots on the top leaves.

Not sure what it is , could it be calcium shortage ?

I add 2 liters rainwater a day without adding calmag to it.
Before i replaced all the water every 3a 4 days,
Last time i waited a bit longer ( 6 days) , could this be the problem ?

Thanks!

Growenhaft · Jan 10, 2022

if you only add one cal / mag product to your rainwater, it is very likely that another very important trace element is missing ... boron.
admittedly, both defects look similar and are often confused.
often remain undetected as a boron deficiency because the addition of calcium in turn strongly supports the absorption of boron. However, there is no boron in rainwater ... and in the fertilizer itself there is usually too little boron ... because it occurs in sufficient quantities in the groundwater and thus in tap water.

it would be better if you enriched your water with the complete trace elements ... not just calcium and magnesium. or you can use part of tap water and part of rainwater.

Mich000 · Jan 10, 2022

I have some other brand calmag its Orange CalMag

that one does contain a bit more then just calcium and magnesium . See thw picture.

Would this be better?

troutman · Jan 10, 2022

^^^ Those trace elements will help for sure.

Mich000 · Jan 10, 2022

Oke just changed the water, added the other calmag with the extra stuf in it,
and i also mixed with tapwater around 10%.

and now fingers crossed.

Thanks

TanzanianMagic · Jan 11, 2022

Mich000 said:
Hi everyone,

Im in the 37 days of flowering, and some of the leaves add the top of the plant have some brown spots on them/

The parched spots look like mildew. If it was outdoors, I would say the 3 spots on top of the leaf look like leaf miner damage. However this far into the grow indoors, I'm sure insect problems have been taken care of.

More aircirculation is the solution. And pruning off the affected leaves.

Mich000 · Jan 11, 2022

You mean Powdery Mildew?
i looked up some pictures of powdery mildew and to me it doesnt look like that ad all.
Its realy burned/dryed out.

the brown spots are all on leaves closest to the light.
I just measured with my smartphone how strong the light intensity was, and it shows +/- 75000 max at the height of the buds.

During day time: humidity 45% temp. 23C (73F)
during the night: humidity 50% temp 21C (70F)

I also emailed Plagron if I had to add extra additions to their basic nutrients because I use rainwater that has nothing in it.
The replied that everything is in there Hydro A+B product even when used with rain or RO water.

TanzanianMagic · Jan 11, 2022

Mich000 said:
You mean Powdery Mildew?
i looked up some pictures of powdery mildew and to me it doesnt look like that ad all.
Its realy burned/dryed out.

You're right, it looks more like septoria leaf spot.

https://growersnetwork.org/cultivat...-networks-disease-profile-septoria-leaf-spot/

However the treatment is the same - more air circulation.

f-e · Jan 11, 2022

The tiny spots don't say enough, but I see some larger areas have gone, that actually do resemble light burn. Real light burn. Then I hear it's at the tops. However, light burn don't always mean that less light is the answer. It's often possible to improve the feed to cope.

Has the light level recently changed? If you just turned them up, I would suggest more mag. If however it's crept in, I'm interested in this talk of boron but think the calmag product change looks good.

Mich000 · Jan 12, 2022

When this started I hung the lamp a bit higher because I thought the burnt pieces also looked like light burn, and because the lamp was also very close.
But the brown spots (on the center of the leaf) didn't look like typical light burns to me.
And the started directly after i changed the height of the light.

Add that time the amount of calmag was quite low as I had only been adding rainwater water with hydro A+B without the extra calmag for a few days.

There a just 12 Liters in the system , the plant is using about 2 liters a day.

After i changed the clamag product i didnt see it progressing.

TanzanianMagic · Jan 12, 2022

When a fungus affects the leaves, it limits photosynthesis and the amount of nutrients the plants can take up, which will result in a nutrient deficiency of whatever the plant is using most of at that time.

Leaf Septoria vs Calcium Deficiency In Cannabis Plants
https://kindseeds.net/leaf-septoria-...um-deficiency/

Leaf septoria will appear as yellow blotches on the leaf surface that turn into brown spots with a purplish hue. The leaf may be crinkled and eventually, smaller leaflets near the center of the plant can wilt from lack of nutrients.

In contrast calcium deficiency looks like small holes in between the veins which appears to have been eaten away by insects or some other pest. In this case it is possible you need more nitrogen but if there are no pests present then it could just mean your plants aren’t getting enough calcium overall for proper growth and development so adding a supplement would help correct these problems over time.

I guess closeups of the leaves would help, and of different angles of the plants than just the canopy.