Something is stripping my tomato plants bare overnight — what is it?
Tomato hornworms are the likely culprit — 3–4 inch green caterpillars that are nearly invisible against tomato foliage and can defoliate a plant in two or three nights.
Tomato hornworm (Manduca quinquemaculata) is one of the most dramatic garden insects. A fully grown larva is 3–4 inches long, bright green with diagonal white stripes along the sides and a distinctive horn at the rear. Despite its size, it blends so effectively with tomato foliage that many gardeners never see one until the plant looks stripped. Look for large black droppings — about the size and shape of small pellets — on leaves and the ground below the plant. Follow the droppings up the plant to find the caterpillar on a nearby stem or the undersides of leaves.
Evening is the best time to look, when hornworms are more actively feeding and the lower light makes their dark droppings more visible. They're easier to spot with a UV flashlight at night, which makes them glow under the ultraviolet light while leaves remain dark. This technique works reliably if you're having trouble finding them during the day.
Hand-picking is effective. Drop them in soapy water or cut them with scissors. A single large hornworm removed promptly ends the damage cycle. If you find a hornworm covered with small white oval objects attached to its back, those are the cocoons of Cotesia congregata, a parasitic braconid wasp that lays eggs inside the caterpillar. Leave those hornworms alone — the wasps will kill the hornworm as they emerge, and the adult wasps will go on to parasitize other hornworms in your garden. This is a free and effective biological control.
Bt (Bacillus thuringiensis) applied to leaves and stems is effective against young hornworms. Tilling the soil in fall kills overwintering pupae. Hornworm pressure tends to build later in the season — mid to late summer — so an absence early on doesn't mean they won't appear.
- Black RotV-shaped yellow lesions at brassica leaf margins with blackened veins inside — a bacterial disease that moves through the vascular system.
- Blossom End RotDark, sunken, leathery patch on the blossom end of tomato or pepper fruit — a calcium deficiency disorder.
- Brown Marmorated Stink BugSunken, corky dimples on fruit and pods caused by a mottled brown shield bug feeding through the skin.
- Cabbage LooperRagged holes in brassica leaves made by a pale green caterpillar that loops its body as it moves.
- Cabbage MaggotBrassica transplants wilting and dying as white maggots tunnel through roots at or below the soil line.
- I have aphids on multiple plants — do I need to spray everything?Aphids tend to colonize plants under stress and naturally crash when beneficial insects find them — water sprays and patience are often more effective than pesticides.
- How do I deal with cabbage worms on my kale and other brassicas?Bt (Bacillus thuringiensis) spray applied to the leaf undersides is the most targeted control for cabbage worms — hand-picking and row cover are also effective without any spray at all.
- Something is cutting off my seedlings at the base overnight — what is it?Cutworms — fat gray or brown caterpillars that live in the soil and feed at night — cut young stems at or just below the soil surface, and a simple collar around each stem can stop them.