|Leafhopper damage to grape leaf. They are on the undersides of the leaves.|
|Dead sphynx moth on the sidewalk. They lead to hornworms.|
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.
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.