A insecticide called merit would work on individual
plants. It has the same active ingredient as Grub-X ( imicloprid ) but you can get in in a wet able powder form so all you have to do is water your
plants with it. It makes the
plant inedible to the insects. And it lasts all season long. Other then that all you could do is periodically apply a non selective pesticide, such as Sevin or Malithion, but those will also take out many beneficial insects, and I don't recommend many repeated uses, although it says you can on the label.
Good Luck
We have the same problem here too, but I have grasshopper eating kiddies
who make it their habit not to leave one little green critter undisturbed. They also do a great job on catipillars,snails,toads frogs, small snakes....ect
