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I've had a kumquat tree on two different balconies for about three years. It's put out a few kumquats over the years, and lately started to again. Recently I noticed this white substance growing on some leaves, something I've never seen before. What is it? Is it dangerous - the tree has been looking fine for months, better than ever, even. If dangerous, what can I do about it?

Click any photo for full size

general picture of kumquat with white growth

You can see it on the bottom right of the picture, below the flower.

Here's a close up:

close up

  • We need a picture that is closer to the white substance. – kevinsky Aug 29 '14 at 11:23
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    I magnified the pic and it looks like a sheet of white fluff beneath a couple of leaves - most likely mealy bug infestation, though magnification still doesn't show enough detail. – Bamboo Aug 29 '14 at 12:29
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    I agree it is probably mealy bug but it's more of a guess than certainty. – kevinsky Aug 29 '14 at 14:37
  • I thought citrus trees were pretty resistant to mealy bugs (I've had them before, though, admittedly, not near the kumquat). – Eyal Aug 30 '14 at 8:06
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Update:

I just found a picture of woolly aphids on an avocado branch:

enter image description here

If this is the case, look for individual insects something like:

enter image description here

When you pull the mass apart.

Aphids are easier to control than mealybugs, and you can simply apply a detergent solution, or spray with neem oil. Be sure you properly identify the pest before choosing a control method.

Older diagnosis, still a possibility:

Looks like a mealy bug infestation. You should confirm this before treating, by picking off some, and locating the insect bodies, which look like this. Yours seem to have quite a lot of 'cotton', which is common, but it hides the insects so identification from photo is more difficult. But I'm pretty sure by the groupings and placement that this is what you have.

There are several ways you can control them, but I use an isopropyl alcohol mixture, which dissolves the waxy coating, and then I treat with neem oil, which kills them. It's a one-two punch that has been around for some time. You can apply it with a paint brush or a cotton swab.

I've heard that a detergent solution will both dissolve the wax and kill the pest, but I fell that in that concentration, it's likely to leave burn marks on the leaves.

If you have a small infestation, one thing you can do :) is wipe them off with a damp cloth, and dispose of them. It's very simple, and works well, with a plant with thick, leathery leaves like a kumquat.

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