Ever seen these black dots before?

5 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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Comments (5)

ken_adrian Adrian MI cold Z5
5 years ago
you seem overly concerned about removing it.. i would not damage leaves trying to do so ...

you have observed such.. now keep observing and see if it gets worse ...

but dont love it to its detriment too fast ... there may be nothing to fix.. lets find out.. before we over react ...

lets make sure there is an ongoing problem .... before we fix it ...

and dont get me wrong research and asking is knowledge.. and knowledge is power ...

btw.. i just used a systemic product in the media of the plants that are outdoors... i want to make sure there is nothing in the media and as it works its way into the plant .. the plant ... i do no surface treat the plants.. as they are not showing any surface issues at this time .... i would hesitate to oil my plants.. when its not needed ...think about that process .. the plant is going to be very stressed just by bringing it indoors.. do we really want to stress the leaves more??? .. on a preventative basis when there may not be anything there that requires such???

ken
michael_ames
Original Author
5 years ago
last modified: 5 years ago
Thanks for this perspective, Ken.

And it's probably the correct one, since it doesn't seem that these spots are negatively affecting the plant at this point.

In truth I was more curious than concerned.

I looked outside the window at the lemon tree this afternoon and noticed a fly land on the railing. With a bit of google searching, I found this image of a fly, which I think solves the mystery: it's some kind of fly excreta (either poop or vomit, I'm guessing). It may be a bit distasteful, but at least it's no danger to the plant!
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Fori
5 years ago
Could be worse...I've got hummingbird poop on my tomatoes. Time to prune back the iochroma tree hard I guess. :)
socalnolympia
5 years ago
I've seen them. They seem to be tiny insect eggs of some sort. I'd remove them. could be a pest that's not good for the leaves. very gently scrape them off with a sharp knife.
Matt Harris
4 years ago
Tree/leaf looks pretty healthy to me. Just leave it, less is more in this case. I have 60 trees outdoors and I’d be jumping for joy if they all looked like that!