That was going to be my next question. I found a 36.8% permethrin solution on amazon.

1/2 oz. of a ~40% solution of permethrin mixed with 1/2 gallon of water will create a ~0.3% solution permethrin.

1 oz. of a ~40% solution of permethrin mixed with 1/2 gallon of water will create a ~0.6% solution permethrin.

I'll let you know how it works.

For what its worth, the internet recommends a 0.25% solution of permethrin for insect control on a vegetable garden.