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The tree In my garden as lots of red cocoons on its leaves, I assume these are insects, do I need to be concerned or are they harmless?

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I don't think those are coccoons. –  JSBձոգչ Jun 8 '11 at 19:36
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Your local extension is probably the best place to go for this. Oh - I see you are not in US - hopefully you have an agriculture office locally you can get advice from. –  Tim Jun 8 '11 at 19:37
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up vote 11 down vote accepted

Here's some Insect advice from Penn State.

In summary, it sounds like you have a mite problem for your tree (take note of the other trees, that looks like a maple leaf to which this insect is characteristic); they are "commonly referred to as eriophyid mites".

  • "these galls are not harmful to the health of a tree. ... Feeding by eriophyid mites appears to stimulate the formation of galls on the upper and lower surface of the leaves... If many leaves on a tree are heavily infested, there may be some reduction in growth."
  • "In general, leaf galls do not seriously affect the normal growth of a tree. Thus, chemical control is seldom suggested. If indicated, the best time to treat an infested tree ... is mid-April, before buds swell"
  • Note that these mites are predated by ladybugs green lacewings, so if you have an infestation of either of those these might be contributing in some way to that.

Gall Mites nymphing it up on a maple leaf

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