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michael__ames

Ever seen these black dots before?

michael_ames
2 years ago

In the past few weeks I've noticed some recurring black dots — almost like ink spots — on the leaves of my container meyer lemon tree:




They feel completely flat when you rub your finger over the leaf surface, but it is possible to remove most of them with a gentle scrape of a fingernail. They leave no discoloration or injury behind. There are only a few on any given leaf, and only a few leaves at a time appear affected. I'm puzzled.

  • They could be scale, I suppose, but they're very small, perfectly uniform in color, and don't have that characteristic slight dome/shell shape. They also seem easier to remove than I'd expect were it scale. I also don't see any evidence of scale elsewhere on the plant.
  • Images of artillery/shotgun fungus seem close to the mark, but I've read it's impossible to remove without damaging the leaf, which isn't the case here. My plant is also on a 2nd floor balcony far away from any likely sources.
  • My last guess is that's it's some kind of insect frass, but I'm surprised it adheres so strongly to the leaf. I can get it off with effort, but I can't gently brush or wash it off.


Anyone seen this before?

I'll be doing some neem oil spraying over the next few weeks before I bring the tree in for the winter anyway, but I'm quite curious to know what I'm looking at here.

I've seen it on a few of my other plants as well — including a very fleshy-leaved jade plant — so maybe its source is more environmental than due to pests?


Bonus question:

I made a version of Josh's (greenman28) moro mix here: about 4 parts screened bark (I used Orchiata), 1 part washed perlite, 1 part washed black lava rock, and I'm curious to see how it goes. I didn't add any lime or gypsum, but the orchiata bark is supposed to be pre-treated with some dolomite. I use foliage-pro at every watering, but I wonder if I should also be supplementing with other minerals (e.g. Calcium or Magnesium) at any point during the year.

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