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Wednesday, April 8, 2015

Leafhoppers, Hornworm and Skeletonizer Reported on Grapes Now

Leafhopper damage to grape leaf. They are on the undersides of the leaves.
I received an email from a reader who reported leafhoppers already on grape leaves. I had another person report sphinx moths flying now (this moth lays eggs that make the hornworm) and another person reported skeletonizer moths (black or metallic dark blue) flying around the grapes.

Dead sphynx moth on the sidewalk. They lead to hornworms.
This came out of Arizona and southern Nevada but would be relevant for the low and middle desert elevations (500 to 3000 ft). If you had leafhoppers last year you can expect them this year. These are tiny little bugs that hop off of the grape leaves when you walk by them. Some people report that they "swarm" or fly off the leaves. They can't really do this but because they are so small and there are hundreds of them it may seem like it. To find them now you must look on the UNDERSIDES of the leaves.

If they are not controlled early, their numbers will begin to build over the season as they continue to multiply. Once the adults get established they are very difficult to control without using some very harsh conventional pesticides.

Skeletonizer moth.
Leafhoppers don't do a lot of damage to homeowner grapes except for the tiny black dots (feces) they leave behind on fruit and leaves. Commercially this is a problem. But they are a nuisance.

One of the most effective treatments when they are young is a spray of Spinosad. Spinosad is an "organic" insecticide. Even though it is organic, it is rough on bees so never spray if flowers are present. Spinosad is also very effective on the "worms" or caterpillars that you find on grapes. This includes the hornworm and the grape leaf skeletonizer.

I would make two applications of Spinosad to the grapes now and repeat it in about 10 days to two
weeks later. After this time inspect your grapes for these three pests and apply it when you first see them. Use a wetting agent like EZ Wet mixed in the spray. Use a hose end applicator or compressed air sprayer (best) and make sure you spray UP (the bottom of the leaves get wet). Repeat the spray on by spraying down (tops of the leaves). Spray just enough to wet the leaves.

Bt sprays will control the skeletonizer and the hornworm but not the leafhoppers. You must control leafhoppers early.

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