My Basils have spots!

[JRComito]

Our Basil has been growing around our property like weeds. When it goes to flower, we prune and propagate directly in the soil. It has been doing wonderfully until recently. Almost all of our plants have these black spots that look like spider webs. Could this be a pest or some sort of deficiency? The one in the photo came from our AP system, but the ones out in the soil are doing the same thing. Someone on another forum suggested it may be a temperature issue. He claimed that his Basil is the first  to be affected by the cold, but he is in Jersey. We haven't seen 60 yet here, so I wonder what temp might be low enough, if that is the cause. Plus, I have seen these spots for a few weeks now, and it has been warm here.

[JRComito]

So I did a little research and found these links:
http://en.wikipedia.org/wiki/Colletotrichum

http://en.wikipedia.org/wiki/Black_Spot_

Anyone think I'm on the right track?

[Vlad Jovanovic]

Well, it certainly doesn't look like any nutrient deficiency I've ever seen (and I've tried to induce just about all of them one at a time or another in different plants)...

I think you may be right in that a fungal pathogen is probably to blame. 

[RupertofOZ]

Yep fungal... basil are very prone.. especially as the plant nears end of life... and/or temps begin to fall off during the night...

[Chris Smith]

We get the same thing on occasion. It seems to happen to us after a more acidic rain than usual. we like to use kelp extract and compost tea as a foliar spray when we get spot or mold issues. Seems to work for us.

[Vlad Jovanovic]

Chris, what you say about the acid rain makes perfect sense. Fungi seem to thrive and 'bloom' at lower pH levels, yet have a hard time functioning at higher pH levels (to make a gross generalization, above 8.3 seems to give them a hard time). Anything that seems to raise the surface pH of the leaf appears to work. And if you can boost the microbial activity at the same time, like with a good worm tea, so much the better. I bet the bacteria are able to 'out compete' the fungus at the 'higher' pH levels. 

Twice over the last year I've manage to "cure" bouts of pythium in the reservoir of small test systems (once with a basil plant, and once with a hot pepper plant) just by elevating the pH (once with KOH and once with NaOH) to an inhospitable degree. This of course has it's drawbacks (nutrient lock-out...when done in a systems water reservoir, which I attempted to negate by foliar feeding)...but it would appear that anything that raises leaf surface pH and is fish safe (for AP) is worth a shot. Worm tea, wood ash (from hard wood trees) and water (rain or distilled water...giving you 'home-made' KOH), store bought NaOH, and potassium bicarbonate (KHCO3) have all been things I've tried using. They all seem to work well, though I'm leaning towards using the the worm tea/and or potassium bicarb in an AP setting. Which kelp extract have you used for this?

[Chris Smith]

I use an "organic" powdered form. It is MUCH less expensive to use powders rather than liquids when living in the middle of the Pacific Ocean. I forgot the name brand. I was able to get a pound of powdered concentrate for less than two bottles of Maxicrop and it works just as good. Been using the same stuff for more than two years.

[JRComito]

Can I add the worm tea to my gravel bed and not harm my fish, or is there a different technique?

Vlad Jovanovic said:

Chris, what you say about the acid rain makes perfect sense. Fungi seem to thrive and 'bloom' at lower pH levels, yet have a hard time functioning at higher pH levels (to make a gross generalization, above 8.3 seems to give them a hard time). Anything that seems to raise the surface pH of the leaf appears to work. And if you can boost the microbial activity at the same time, like with a good worm tea, so much the better. I bet the bacteria are able to 'out compete' the fungus at the 'higher' pH levels. 

Twice over the last year I've manage to "cure" bouts of pythium in the reservoir of small test systems (once with a basil plant, and once with a hot pepper plant) just by elevating the pH (once with KOH and once with NaOH) to an inhospitable degree. This of course has it's drawbacks (nutrient lock-out...when done in a systems water reservoir, which I attempted to negate by foliar feeding)...but it would appear that anything that raises leaf surface pH and is fish safe (for AP) is worth a shot. Worm tea, wood ash (from hard wood trees) and water (rain or distilled water...giving you 'home-made' KOH), store bought NaOH, and potassium bicarbonate (KHCO3) have all been things I've tried using. They all seem to work well, though I'm leaning towards using the the worm tea/and or potassium bicarb in an AP setting. Which kelp extract have you used for this?