Safely and easily make your plants resistant to pests! SNS 209 All Natural Systemic Pest Control provides a barrier for plants to protect them against damaging insects. How it works: SNS 209's unique formula works by allowing the plant to uptake a small amount of rosemeric acid from the rosemary plant. When an insect starts to suck or chew on the plant, it comes in contact with the rosemeric acid and causes the insect to stop eating, move on or die.