Lets Talk About Rust Fungus & What You Need To Know.

VX420 said:

I would think if you had a fungus you would be able to wipe some of it off the leave. There are ALOT of probelms that look like the OP. Lack of P looks like that.. Not saying its not as claimed, I have had no experance with it myself. I just think if you had a fungus Like all other fungues you could wipe some of it off.

Looks like I have some reading to do.

From the OP Post;

Rust is most commonly seen as coloured powder

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It's most def rust fungus

Twelve0seven said:

I think I have this problem, the only difference between mine and those is they yellow and curl up after the initial rust on the leaf ends. Do you think that would be rust disease or something different?

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Deficiency

its calcium deficiency

My battle with "rust fungus" aka Septoria began with tomatoes. I stupidly watered by spraying the entire tomato plant, which would make some leaves touch bare soil. These leaves that touch the soil are how the fungus gets started spreading across the plant.

Now that I'm growing cannabis, the same issue has come up but I know how to deal with it. Here's my checklist.

Preventative:
1. Don't let soil touch the leaves. Use mulch as early as possible and don't let ANY soil touch your leaves, EVER.
2. If you foliar feed, make sure that it dries fairly quick to avoid providing a humid environment for septoria to spread.
3. Spray diluted copper fungicide once every 2 weeks in veg.
4. If you notice black, sticky spots showing up, that eventually turn into burn marks or holes, you need to handle it ASAP before it spreads. These sticky spots are the giveaway that it's not a nute pH problem.

Cure:
1. In veg, copper fungicide is an absolutely amazing cure. Spray in the mornings.
2. In flower, either use sulfur burners or get ready for a lot of work. Make a bowl of copper fungicide and dip a paper towel, wiping down all leaves but not buds. DO NOT SPRAY COPPER ON BUDS IN FLOWER.

This stuff really works. It will stop spreading immediately, no more black sticky spots. Burn marks don't recover but it's on you to spot this early and use the preventative measures (remember, mulch). Don't let soil touch your leaves.

Here's what I use: https://www.amazon.com/Southern-Ag-Liquid-Copper-Fungicide/dp/B007PJUJG4

Cheers.