Rust looking brown spots on leaves

Strain; Afghan Feminized
Day 19
PH: 5.8
TDS 610
Indoor 4x4 tent
Light system 1200W LED @24" away
Temps; Day 77, Night 75
Humidity; Day 38, Night 38
Ventilation system; Yes
Co2; No

Hi All,
This is my first grow and I have a problem. 2 out of 4 plants have developed rust looking spots on the leaves. Came on quite suddenly within the day. Can anyone please tell me what this is? I’m growing for Medical purposes only so it is very important that I be successful to the end.
Thank you!


Have you used any nutrients?

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Yes, I’m using Advanced Nutrients Grow, Bloom and Micro and following the instructions. I’m also taking into consideration the TDS out of the tap which is 174.
TDS: 610

Do you know what the make up of your 174 PPM tap water is? That looks like an early mag deficiency to me (but I’m not expert, and I did not stay at a Holiday Inn Express last night, so I can’t pretend to be one either).

You putting any kind of calmag in?


I’ll go to the Water Dept’s website, pull the report and get back to you.

First I would put that very powerful led a bit further away at least 30"

If I were a betting man that sure looks like calcium mag. issues. Led will always tend to create cal/mag issues in grows.


Question…If I were to treat for Cal/Mag and it were not the issue. Could I do more harm?

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I’ll move the lights right now.

Not likely to do more harm. At the size of your plant you’d like only be adding 2ml/gal of calmag to your water. I personally am a huge fan of adding silica during veg as well.

I run DWC in 14 gallon totes and have used 2.5ml of calmag per gallon (I use GH Flora series nutes) the entire grow (I’m on week 7 since the flip).


So it would be a deficiency rather than too much?


Cal-mag and make sure your ph isn’t floating around on you


Yes it’s a deficiency from what you have stated you use for your plant.

I grow with only led so I have gotten used to the trend. I use the following product religiously. I love it because it’s NPK is 0-0-0. Perfect so that you don’t throw off your nutrient schedule.



If you are giving full nutrients according to the manufactures schedule then most likely you have a different issue. @cmichphoto

Are you checking your temps, pH and TDS frequently?



Welcome ti ILGM.

Here is what I believe it to be

Rust is a fungus problem that can affect nearly every green and leafing plant. It’s descriptive, rusty name comes from the reddish, brownish or yellowish color that it causes the leaves to turn, and also for the spores that appear powdery and will rub off on anything that touches the affected leaves and will spread on the slightest air current. Controlling rust and curing plants affected is simple.

Remove Infected Leaves and Stalks

Remove leaves on plants that are infected immediately. If rust infects your turf grass, regular mowing with a bag-style mower will help to do this. Prune away infected plant stalks as soon as the plant has finished its blooming cycle. Never compost this infected organic material. Composting infected organic material can cause it to infect the resulting mulch and loam. Instead, burn the infected plant leaves and stalks to control the spread of the fungus.

Use Sulfur and Fungicides

Use sulfur or other fungicides to kill the surface spores and clamp down on the spread of the infection to other plants. Plants should be treated every 10 days with fungicide. According to Drs. Buck and Williams-Woodward at the University of Georgia, you should change the fungicide that you use periodically to prevent rust from developing a tolerance to it. Sulfur used on a lawn will also help repel insects such as mosquitoes and ticks, but must be reapplied after each rain.

Adopt Preventative Measures

You can stop the spread of rust and help to bolster rust-infected plants by increasing the overall “hygiene” of a plant. Rust is a problem in areas where plants are exposed to moisture for long periods of time, such as hot, humid areas where dew does not dry. Increasing air circulation around and through a plant will help it to dry faster and create conditions where rust cannot thrive. To do this, space plants such as day lilies, roses and fruit trees and bushes farther apart when planting. Additionally, prune plants such as roses and fruit trees and bushes so that air can pass through their center mass more easily. Finally, adding organic fertilizer such as compost or liquid fertilizer in the plant’s water system will help to make a plant healthier. Healthier plants will be able to resist infections of rust and other fungus more effectively than unhealthy plants in the same way that people who take their vitamins are more resistant to the common cold.



Now that I look closer I see the aerated edges on most leaves are turning up, so maybe some heat/light issues going on here too.


The best way to tell is to place your hand just above your plant if the back of your hand feels uncomfortable then so will your plant and all you’ll have to do is lift your light.
Now if the light is ok and it’s hot in your grow it’s best to get your room cooled down.



So you think it’s a rust fungus? @garrigan62


Rust, how many of you have had this and been beaten by it? lots i bet!!!
first, rust is a fungi. it is opportunist. it preys on unwell plants. if something is a miss, rust is a sign. rust has been identified to have 7,000 species. it attacks crops of every description. but we’re only interested in one variety aren’t we?
if rust is present early in a grow, you have problems as it’s an indicator something in your room is a miss. usually ventilation. go through your system and double check things are in place and working properly.
rust is an air borne fungi. if given the opportunity, it WILL take hold. it usually does during flower as this is when the plants immune system is at its weakest as its energies are concentrating on re-production, not survival.
depending on what part of the grow you get it, you can cure/minimize it with either chemical or natural remedies.
it enters the leaf via the stomata and then it’s off and running.
fungicidals used are generally copper based and include; thriram, manzecob, maneb or zineb at 10 day intervals.
baking soda, 1 tea spoon/ quart of water. spray on.
copper sulfate, read labels.
fungicidal soap sprays;
garlic sprays, 1/2 cup minced garlic, 1 quart of water. let sit 24hrs, strain, spray.
sulfur, one of the best natural sprays. it is low in toxicity.
micro kill, a citric based killer. i use this with great success


Hi All,

Did you know there is a restriction on the amount of responses a new person can make? I was locked out for 24 hrs…ridiculous!

Here is what it looks like today. I went to the Hydroponic store yesterday after seeing everyone’s opinion and showed the owner my picture. He thinks it’s Cal/Mag deficient too! Hard to know who is correct. I bought Cal/mag and added it in as I wasn’t using any. I will also try the baking soda and will try to find micro kill.

The temp in the tent is maintaining 77 when the lights are on and drops to 75 when off. Someone noticed the curling happening on some of the leaves. Could this be from a Cal/Mag deficiency too? Temp seems fine.

After seeing today’s picture…what do you think?

Thanks for all your help.