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I recently bought a bonsai tree, and today I noticed a white residue on one of the leaves (see photo). Is this some kind of normal plant thing, or is it a disease or fungus that I need to deal with?

Some context in case it matters:

  1. The tree sits in a window that gets a little bit of sunlight (best I could do), with a grow light hanging over it.
  2. I watered it five days ago and have checked the soil daily since, but it hasn't seemed dry enough to warrant further watering. (Could I have overwatered it on that one shot?)
  3. It's a fig tree of some kind.

enter image description here

  • Some people use milk to make fig leaves shiny. From the splashes on the other leaves, it looks like somebody made a mess when trying to do that. – alephzero Oct 26 '19 at 10:42
  • Since it wasn't me, the only other candidate would be the man at the nursery... Is that a thing they do to sell trees? – crmdgn Oct 26 '19 at 13:19
  • Whilst some of the white marks are due to some sort of leaf shine probably applied at the nursery, I'm not so sure about the two leaves on the right. Unfortunately, the picture is not high resolution enough to magnify well so I can't tell what the white deposits on those are, but take a magnifying glass and inspect those areas thoroughly, as well as the underside and stems of leaves. Might be mealybug... – Bamboo Oct 26 '19 at 20:42
  • @Bamboo How will I know? What am I looking for? – crmdgn Oct 27 '19 at 21:06
  • small bugs/insects within the white deposits, especially if the deposits are cotton like. – Bamboo Oct 27 '19 at 21:11
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This is hard water residue or pesticide residue. Wear disposable gloves and use a soft cloth to wipe off. It will not reoccur.

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There are four reasons why you get residue spray from the grower;

They added fertiliser to the sprinkler lines. This salt residue is then left behind on the plants.

If the grower is using well water with out an inefficient filtering system the hard water, as Kevinsky pointed out will also build up on the water.

Some growers will can add various pesticides to the sprinkler line or go in by hand and use a backpack sprayer to spray both the top, under the leaves as well.

***If they are growing crops that are sensitive to burn under the sunlight they add a Calcium Carbonate spray. This spray will protect the plants, but it leaves the WORST residue on those crops. But if the grower has multiple crops with different sunlight requirements in one greenhouse they will use this spray. They don't have a choice, unless they have a state of the art greenhouse that can block sunlight in just one small part. Also woody crops after often pushed out of the greenhouse to sit outside in the blazing hot sun. Those crops need to be protect with something like; Purshade

IF the sight of it bothers you, use a soft microfibre cloth to gently wipe it off all of the leaves. Otherwise it is safe to leave on the plant. Make sure you are gentle, do not try to scrub it clean. If it all doesn't come off try again in a few month. Most of it will come off over multiple wipes, but never force it. Always use a sofy microfibre cloth.

Purshade protecting plants from sunburn

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