September 3 - my friend Sarah sent me the following email:
"What's eating my new rhododendron?! It's got all these little notches chewed into the edges of the leaves, but there's no sign of critters on or under the leaves."
The damage you're seeing is being caused by root weevils. They can also bother Nandina ("Heavenly bamboo") and strawberries, among other things.
They live in the ground, and crawl up the trunk to the leaves during the night. A simple way to stop them is to put a 1-2 inch wide band of Tanglefoot (a very sticky substance made just for this sort of thing) completely around the base of the trunk, up a few inches above the soil - they'll get stuck in it. You need to put it on thick so there are no gaps, and high enough so rain/irrigation isn't splashing lots of dirt onto it, since that'll basically stick to it as well. They aren't very big bugs, if that sort of thing bothers you.
If you don't want to do that directly on the trunk, tightly wrap a ring of thick paper or cardboard around the trunk, and then put the Tanglefoot on that. That'll let you cut away the paper and keep things looking a bit neater - although unless the rhody is quite young, the trunk isn't generally in plain view anyway.
There are probably chemical soil insecticides you can use, but I try to avoid them - they tend to poison both the good and the bad bugs.
For more information, please check out this Oregon State University fact sheet.
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This page was last updated November 18, 2013