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I've been growing this basil plant for a couple of months. I started it from seed in a rockwool cube. Here's its environment:

  • It's under full spectrum lighting for ~15 hours per day, and I recently switched from a 35W fluorescent to a 24W LED, both are designed for horticultural lighting. No sunlight unfortunately.
  • It's been growing in a well aerated deep water cultivation fed by Botanicare Pure Blend Pro (the Grow 3-2-4 formula) at about 5ml per liter of water, as the bottle suggests.
  • The nutrient solution has been completely replaced once, and that was a few weeks ago.
  • It's in an apartment that varies between 22C and 26C, and the nutrient solution reservoir seems to stay between 23C and 24C.
  • Relative humidity varies between 20% in the late afternoon and 80% in the morning.
  • The system's pH is currently just above 5 (tough to get accurate readings with tester drops), which is where I adjusted it to after changing the nutrient solution, so it's steady.

Here's the plant next to its cilantro neighbor:

Cinnamon Basil Plant

It's growing well, the leaves are fragrant and full, and I notice new growth every day. Happy days.

But I've noticed some light spots on the leaves that don't look healthy to me:

light spots

shiny dead spots

The first picture shows small light spots, and the second picture shows small dead spots that are actually a bit reflective/shiny. The affected leaves otherwise appear healthy, with good color and not even slightly wilted. Many leaves on the plant are affected, and the issue isn't localized in any one area of the plant.

I've looked very, very closely at affected leaves, unaffected leaves, the stem, the growing substrate, the surrounding area - there are no visible insects crawling or flying or worming around. I had a good look through some related threads (here, here, and several others that weren't related enough to link to), and decided to actually dissect a couple of leaves to look for leaf miners. But I saw nothing of the sort. Even with a magnifying glass, I saw no sign of anything alive. Nothing that looked like "trails" of eaten leaf. No bumps in the leaf or veins where they might be hanging out. No dark spots or anything that looked like frass.

What else could be causing those spots? Does anything listed in the plant's environment look out of wack?

  • Did you check beneath the leaves? If not, do so, preferably using a magnifying glass – Bamboo Sep 2 '17 at 18:32
  • Hi @Bamboo! I looked closely under several leaves, both affected and unaffected leaves. I even cut a couple apart to look for pests. But I didn't use a magnifying glass, I'll try that now. – kdbanman Sep 2 '17 at 19:53
  • Just had a look at the underside and top side with a magnifying glass. It's not the best glass, but definitely some magnification. I saw no sign of anything alive. Nothing that looked like "trails" of eaten leaf. No bumps in the leaf or veins. No dark spots or anything that looked like frass. I'll toss this in the main post for context. – kdbanman Sep 2 '17 at 20:02
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We'll need more information of course. This could be nutrient deficiency; a few likely suspects are; copper, calcium, manganese, boron or magnesium or...thrips or even a virus. What is your pH? That is critical for your system. It should be 6.5. Lower will cause problems as well as higher for uptake in your system. My initial feeling are thrips...tiny dudes.

I am glad you looked for leaf miners. Do you have your air filtered?

Here is an excellent diagnosis link...it is for marijuana but I use it for everything.

leaf symptoms

  • Howdy @stormy. I had a very close look all over the plant and surroundings for insects with a magnifying glass. I didn't see any thrips, and I was looking for stuff that small. But I think you could be right about pH. My system is currently near 5.0. I don't know how close, because I don't have a digital meter. Basil in soil likes close to 7.0, so adjusting for hydroponics means I should probably try for 6 to 6.5 like you're saying. – kdbanman Sep 2 '17 at 21:39
  • Did you get that link I sent? Super for pH and 'nutrient' uptake and symptoms. 6.0 to 6.5, yes. Read that link and let me know if something jumps out at you, grins! – stormy Sep 2 '17 at 22:58

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