Thrips or Thysanoptera are small, slender insects with fringed wings. When they attack basil plants it is important to control them with organic methods. It is possible to kill them with insecticides, but the down side is that insecticides kill beneficial insects as well. You have to be careful when treating basil that you don't use something that leaves will absorb, because you use the leaves in food preparation.
Water the basil to keep the area moist. Thrips like to eat plants that are drying out. Mist the basil daily to make it a moist environment.
Put down a 4- to 6-in. layer of organic mulch early in the spring to keep the thrips from laying their eggs in the soil.
Leave a weed border around the basil plants. This may look like you are a lazy gardener, but thrips love to eat weeds. Once the weeds are gone, the thrips have a tendency to move to the basil plants.
Add some shiny aluminium foil strips to the top of your mulch. Aluminium foil tends to disorient the thrips, and they will find a different area to lay their eggs in.
Sprinkle diatomaceous earth around the basil late in the evening or at night. Glass-like, it cuts through their exterior. Diatomaceous earth does not distinguish between good insects and bad, so it will control and kill both.