Might this be Tobacco Mosaic Virus? OR nutrients, or watering?

[jalapeno]

My 6 plants are growing vigorously in Fox Farms Ocean Forest soil in 2 gal. cloth pots in a grow tent. A few leaves on a couple of them have these brownish splotches, and/or withered looking brown leaf tips. I had been watering them alternately with pH 6.8 water, and with general organics biothrive grow @ 2tsp / gal, also pH 6.8, But at the time these pictures were taken, couple days ago, soil pH using analog soil probe was above 7, so thinking that might be causing a nutrient problem, I flushed them wit pH 6.0 water, bringing soil pH down to about 6.8.

Not sure if that had any affect. Suppose, I should at least pull any weird leaves, and see if I'm getting new ones after a few days.

I just switched them over to bloom 12/12 lighting, took off a few lower branches, and put cuttings in my clone dome for the future. If there really is a virus, then all my clones may be at risk as well, as I did not separate my cuttings by what plant they came from, since all of them are the same strain (ACDC).

[Mr.furley]

Jalapeno,
it could be possible but I think you are looking more look a potassium deficiency probably due to your PH. I would try and round your PH down to 6.5 on your run off. If you have move your light schedule to 12/12 your plant is going to start needing more potassium and phosphorus in a more stable pH environment maybe while you're seeing the sign, do you have flowing nutrition? Do you add any cal-mag?

[Canuck147]

I would say nutrient lock-out. Nutrients are only soluble to your plants in a pH of 5.5 - 6.5. Which means if your water is not within those parameters (either too acidic or too alkaline) the nutrients dissolved in the water precipitate and become unavailable to the plant.

[NebulaHaze]

Yes, I agree it doesn't look like a virus. It reminds me of problems with pH.

PH Problems



Cannabis plants like a slightly acidic root environment. As others have said, in soil the optimum is 6-7 pH, and in a soilless medium like coco (or if you're using a lot of mineral-based liquid nutrients) you are better off at 5.5-6.5 pH. This is because different nutrients take different forms depending on the pH, and your plant is able to absorb some forms but not others.

I think you already took good steps. If I were you, I would continue giving water at 6.0 pH until the runoff pH of your soil starts coming out lower.

Is it happening on all your plants or just a few? If only some, are there any differences between the plants with symptoms and the ones that don't?

[jalapeno]

Thanks! Love your site. Fantastic service to the community, and where I go to learn, learn, learn.

It's helping already. I decided to remove all the affected leaves so it would be easy to tell later if the problem had been addressed, and lo and behold, there were none. The same leaves no longer showed the yellow/brown patches. Our tap water is not only high pH, but has very high alkalinity (very hard). This seems to cause pH to drift back up from an initial reading after treatment with acidic additive. At least that's my experience with our spa water.

So besides making sure that my solution is at the lower end rather than the upper end of the 6-7 range for soil, I've added pH down today to water I will use tomorrow. That way I can check to see if it's still where I want it to be, and adjust further if necessary before I water the plants tomorrow.

Earlier on in my first grow efforts, using the same strain and soil, I had found that runoff was always about the same as whatever I was putting in, so I stopped checking the runoff, and when I added some plumbing, on this, my second grow, I did not properly allow for run off testing. That's been addressed.

All my plants are the same strain (ACDC), same age, same soil, pretty much same history, and close to the same size. Not every plant showed this symptom, and only a few leaves on the ones that did.

I do have an analog probe for moisture and pH, which is how I realized that the soil pH was higher than what I was putting in it.

[NebulaHaze]

Glad to hear your plant seems to be doing better! It sounds like you're really on top of it.