Isopropyl and water will leave the least residue, natural insecticidal soap, but try not to spray the buds what ever you spray. beneficial bugs of some sort could be a option too. Introduce thrip predators: Insects such as thrips predatory mites, minute pirate bugs, ladybugs Trichogramma wasp and lacewings love to munch on thrips and can help to reduce thrip populations. Use a natural insecticidal soap: These work best for moderate infestations.