I use Listerine about 20% in sprayer bottle of water with one drop of Dawn. Works for me.

I'll bet insecticidal soap would work too.

Thank you very much! I've already spent an hour today squishing worms but am losing the battle. I'll try anything.

You are welcome. I'm sure you could make a little stronger if needed. I get some ideas from Jerry Baker, but won't use all his methods.
Good luck.

Its probably sawfly larvae worms. I had them eating my hibiscus leaves a couple months ago, and they are small-ish green worms. I used a root fed systemic insecticide, because I didnt want to kill the beneficial insects and praying mantis' etc.... It got rid of them completely. But now we have zillions of Japanese beetles eating the other hibiscus, the Rose of Sharon....As well as the Sand cherries, the dahlia flowers, etc. I keep treating one plant, then they eat another!