Have you tried insecticidal soap. It's environmentally friendly and is great for getting rid of soft bodied insects like caterpillars. Spray them first thing in the morning so the plants can dry before the hot sun hits them or early evening so the plants don't go to bed wet

I forgot to add--spray the caterpillars not just the plant. Insecticidal soap has to land on them to kill them. Diligent spraying should get rid of all of them

Thanks dowlinggram.

I have actually used insecticidal soap and I didn't have much luck. I sprayed the caterpillars and the plant and the next day they were still happily munching away.

I also did an experiment, I got three containers and in each I placed a flower bud with a caterpillar on it. I sprayed the caterpillar in each container with a different pesticide - one with confidor, one with pest oil and one with 'safe insect killing soap'.

I checked them all an hour later and they were all still alive and eating the buds. The next day I checked them and the same thing. It seems these things will survive a nuclear blast.

The next thing I am going to try is Bacillus thuringiensis. Apparently it's a bacteria that kills the caterpillars. Have you had any experience with this? I bought some sachets but I'm unsure if I should use the solution as a surface spray, or mix it in a watering can and water the plants with it.

Hello, I was interested in knowing if you were able to control the caterpillars? I’m having the same Issue!

Hi All, Any luck finding a solution?

I had some satisfaction with a spinetoram based pesticide (Yates Success Ultra). But it requires spraying every few days to keep them under control. I think it depends on your area whether or not you can grow pelargoniums without having caterpillar infestations. Warm summers and coolish winters are an ideal climate for the moth’s life cycle.