That is a tough question but a common one gardeners ask. There is not a really good way to control grasshoppers since new ones are always moving in from surrounding areas.
You could try applying an insecticide to the leaves to kill the insects. However, treating the plants with pesticide may kill grasshoppers that eat leaves, but more will simply migrate in thus rendering that option not so effective in preventing damage. There is a natural spore that is quite effective against nymphs. It is known as Nolo Bait. However there is still the problem of the insects migrating in from an untreated area.
Another option is to cover the plants with a lightweight, spunbound polyester rowcover fabric or some type of fine netting. This can help protect the plants from the grasshoppers. However, during an especially bad invasion last year I spoke with a friend who stated that grasshoppers had eaten their way through the rowcover!
Thanks for the question. Please stop in again soon!
Q&A Library Searching Tips