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Monday, May 13, 2013

Watch for Grape Leaves Disappearing - Skeletonizer Flying

Q. I just sited my first grape leaf skeletonizer moth. I’ve learned that Bt will control the worms.   I’d like to try and minimize the larvae if I can by eradicating as many moths as possible. Can you recommend the best course of action, if any, to control the moth itself?

Grape leaf skeletonizer adult moth
A. Not a lot of people know what they look like. They are a dark, blue-black moth that resembles a wasp more than a moth. I will post a picture of the moth, eggs and damage on my blog for all to see. If you have grapes, everyone should start looking for these guys.

Grape leaf skeletonizer larva feeding ont he underside of grape leaf. This picture courtesy University of Arizona
and can be found at http://cals.arizona.edu/yavapai/diagnostics/Assets/Images/Insects/grapeleafskeletonizer1.jpg
            The adult only lives for about three days. Pretty much its sole purpose is to reproduce. The damage comes from the larvae eating the leaves, not the moth eating the leaves. The eggs are laid on the bottom of the leaf. The life cycle of the insect is about 60 days (two months). It takes about 7 days for the larvae to hatch from the deposited eggs.

            I know you want to control the adult in an attempt to control the young but it probably is not the best approach since the adult will be hard to kill. Soap and water or insecticidal soap will work IF the soapy water comes in direct contact with the moth. But since the adult does not eat the leaves, you would have to actually spray the adults to kill them.

            The larvae are fairly easy to kill since they eat grape leaves. You must spray it on the bottom of the leaves. Do this by pointing your applicator so it sprays up, on the bottom of the leaves. The Bt (Dipel, Thuricide) has about a one week residue on the leaves.

            Spinosad will also work and has about the same staying power but is a little harder on bees.
A word of caution: These larva are nasty critters. If a larva falls on your skin it will feel like you were burned by a matchhead.

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