Question
QUESTION: I've got a two year old Bloodgood in partial shade that is doing very well. Most of July has been very hot and dry here in Maine, but the last week we've had very humid weather and some heavy rain. I keep the tree well watered and mulched when it is dry and hot. I noticed today that there are small holes and abrasions on the leaves, almost as if a bug had eaten one layer of the leaf and also had eaten through it also. I haven't seen any pests on the leaves. Nearby there is a hosta with small holes that are definitely from slugs. Is there a connection here for the Maple? Any other ideas? Thanks.

Any ideas?


ANSWER: I would not think the slugs on the hostas would effect the leaves on the maple. There are a few insects that eat leaves mostly caterpillar type. One that eats the layers of the leaf is the Maple Trumpet Skeletonizer .
These insects eat the "green" off the leaf leaving the mid vein and ribs. There several of these usually depending on the species of tree it is on. I would guess in your case it is the maple trumpet skeletonizer Which also attacks maple. Here is a web link maple trumpet skeletonizer

http://www.forestpests.org/vermont/mapletrumpetskeletonizer.html
Usually the insect has done it damage before anyone see the problem and has completed its life cycle and therefore can not be controlled easily. If you can find the insect still feeding on the leaf then there are insecticide sprays that can be used to kill it. There are usually two life generations per year--one in early May-June and another in July-Aug. One large tree it is not recommended to spray since the tree will leaf back out and what you usually only have is some growth loss.

There are other caterpillar type insects that also eat the leaves most eat holes in the leaf rather than just the green area.
If the caterpillars are present than you can spray an insecticide like Bt on the foliage and this will kill the insect. With Bt the caterpillar eats the insecticide and dies a day or so later. Bt is good only for caterpillar type insects and will not harm other animals or insects.



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QUESTION: The damage on the leaves is not that extensive and there are no larvae to be seen. I went to a very good nursery in my area and they are also experiencing the same damage on the Bloodgood Maples but not on the finer leaf Japanese maples. They also do not know what is causing it. They doubt it is a fungus. Thanks.

Answer
If it is not extensive the I would not worry about it. If the areas on the leaf do not exceed 50% of the leaves surface than the tree health is not effected. The tree has grown about all it is going to this year so the loss of leaf surface will not affect the trees growth.