Organic Control of Tobacco Hornworms on Tomato Plants

Every summer, tomato gardeners face a familiar foe: the tobacco hornworm. These large, green caterpillars can strip a plant of its foliage in days. If you're tired of hand-picking them, there is an effective organic barrier you can use.

How Diatomaceous Earth Works

Diatomaceous earth (DE) is a powdery sedimentary rock made from fossilized diatoms. Its microscopic sharp edges abrade the waxy cuticle of soft-bodied insects, causing them to dehydrate and die. Lightly dust the leaves and the soil around the base of each tomato plant. The powder must remain dry to work, so reapply after rain or heavy dew.

Application Tips

• Use food-grade DE, not the pool-filter grade.
• Apply in the early morning or late evening when bees are less active.
• Wear a dust mask to avoid inhaling the fine particles.

By mid-summer, rainfall often decreases, reducing the need for frequent reapplication. Combined with regular scouting, DE can keep hornworm damage to a minimum without synthetic chemicals.