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This is my 3rd attempt at basil on my AP system. 1st was purchased and the other 2 grown from seed. After a couple weeks this black spot infection seems to appear. It also happens on the ones I left in soil. I really love using fresh herbs from my system, and want to add basil to the mix!  Any ideas? 

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It looks it wet? Or is that just glare?

Yea it's wet, been raining here in south florida.  I suspect it might be humidity, which I can't control. 

Molds like damp conditions. High humidity/ poor air circulation is the typical cause; my guess would be that's why those spots are developing.

Damn. Since I can't control the weather, I guess I don't get to grow basil...   Thank you Alex for the reply.

Just put a fan on it and hit it with some potassium bicarbonate Kelly. You can do it!

baking soda spray might help

Fall (less humidity) will help

I've had the same problem but not currently.

Try to get rid of the old leaves

There is a good chance you have bacterial leaf spot (Pseudomonas cichorii) If so it will effect all leafy greens until the conditions improve to prevent the spread of the disease. Sometimes if you buy nursery plants they will carry things you don't want in your system. This is a good page to read Don't do what they suggest with the copper fungicide - it will kill your fish.

The exact same thing happened to me 3 years ago. The best bet is not to grow leafy greens for 6 months and then try again. Try tomato or pepper plants in for the time being.

I did have trouble with purchased plants so I stick to grown from seed. The lettuce and other leafy greens do not seem to be susceptible to this. It happens both in AP and soil, so I'm thinking it might be the humidity.  But I am going to try the baking soda idea to see if I can fight back. (George, what ratio of baking soda do I use?) I may have to wait for Fall, but right now I will experiment to see what helps. I will plant more seeds and try one indoors in the AC without the humidity to test the theory.  I really appreciate the help.  thank you

1 tbs per gal.  

You might might want to get potassium bicarb suggested by Ryan, too.  That along with calcium hydroxide is what I use to raise PH.

I have recently experienced the same problem. I have a very small 2 gallon aquarium system for my herbs. My basil recently developed black spots. I did not notice any of the light green areas around the black spots as displayed in the photo above, but I removed the leaves immediately. The plant is very young and I started it from seedling, other than a black spot here and there the plant is very strong. My plant is not damp it is grown indoors. I will try the air circulation idea and see if that helps and keep you posted on my experience.

If the problem continues I will try the potassium bicarb and calcium hydroxide suggestion. I would like to know if this will harm the fish? With such a small system the only fish I have are a couple of guppies. Any advise would be greatly appreciated. Thanks...

Dear Kelly, This is such a nice picture. I am a  new AP subscriber and this is my first post. I will humbly and carefully respond to the issues you raise. I completed my master gardener cert last year and am now effectively an intern. I also worked as  a plant consultant in a  local big box  store this spring. My contribution was in the area of plant disease and distress. So take what I share along with a  grain of salt. First in response to the thoughts about bacteria, Bacteria will always be a little swishy to the touch.(wash hands with bacterial soap immediately after.) You picture does not seem to show that. A black spot is almost always fungus.  When the outside of the leaves are affected;  for most leaf plants, the problem area is in the roots (too much water or too little oxygen. ) The roots of a   healthy plant need to breathe (5%-20% of the total respiration.)  When the center of the leaf (and working out) is yellow or pale green it is typically a  water shortage, but can be a  nutrient shortage as nutrients are assimilated with the water.

Your spots are on the outside and I would think that the fungus is resident in the roots. Simplest is to gently wash the dirt from the roots, with trickle of water  (with clean scissors) trim the discolored roots.. Then replant it in a mixture designed for propagation (1/3@ sphagnum moss, pot soil, and vermiculite mixed well..) 

When it has nice white root sprouts, re plant it in desired medium. If you have a "Hydro" system, you probably could use an air pump. other wise use some little foam blocks(1/2" foam) to raise the support structure a little higher (than water level) so some of the roots will naturally convert to air source roots. If you have soil medium, water once then let the guy set until it is relatively dry (almost to point of discolor. As the water is used and evaporates, it will draw air into the vacuum left by the water vacation. )

Basil  is typically a dryer climate plant and Florida moisture and air humidity may well stress it. The leaves seem to be  a little larger than I am used to seeing in Texas and that may reflect it's trying to get more  air surface area. Low light will also cause leaves to grow larger than normal.If you have seeds that are naturally adapted to your climate and temperature try them. Other wise limp along until you can make your seed and gradually (5-7) generation, your plant will acclimate itself to your climate. (Each cycle take the first seeds that can be harvested, replant; then repeat until the little guys are all health. ) 

You might find a better answer, but I share the little that I know. And that too is for Texas. If you are not adverse to using chemicals, Bayer Advanced makes a  fungicide derived from naturals, It comes in a  highly concentrated (teaspoon per quart.)  Spray (stream) in the soil on the side of the affected leaf, (within a  30% arc) This will knab the active culture, but the real problem is the moisture. The plant is under stress and this opens the door for the disease. 

 For accurate diagnosis of the particular fungus : They have the capacity to to have a graduate student analyse the exact nature of the problem; then return with an answer. IT IS NOT FREE; BUT THEY ARE very nice.

I have subscribed to your post and hope to find out how the thoughts work.hh

Hi Kelly...bust out your magnifying glass and check the undersides of the affected leaves Beneath the lesions). I'm betting if you check really carefully, you will likely find a slight grey fuzzy growth. If you do you can chalk your problems up to Peronospora belbahrii. 

It's not classified as a true fungus, but rather a type of mold that affect herbacious dicots (of which basil is).

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