What’s Eating My Plants? I

Tobacco Hornworm

Don’t you just hate this? One day you have a perfectly healthy plant, and the next time you look, the leaves are riddled with holes, or completely gone! Just 2 days ago, I photographed a lovely stand of Nicotiana mutabilis (Flowering Tobacco). As I walked by this morning, I was stunned by totally denuded stalks. On closer inspection, there was a 4″¬†Tobacco Hornworm chomping away, leaving behind a trail of excrement. Not a pretty picture now.

The Tobacco Hornworm Manduca sexta is the caterpillar of a type of Sphinx Moth or Hawk Moth. It differs from the Tomato Hornworm by having a reddish instead of a black “horn”, and you can also tell the difference by its lateral markings. The Tobacco Hornworm has seven diagonal lines, while the Tomato Hornworm has eight v-shaped markings.

The adult female Sphinx Moth deposits her translucent green eggs on the undersides of leaves of plants in the Solanacea family, especially Nicotiana (Tobacco), and take 2-4 days to hatch. During their larval stage, these Hornworms feed on the foliage, flowers and fruit. They can ingest the toxin Nicotine without ill effects, and their voracious appetites allow them to strip even large plants overnight. Their green bodies camouflage well with the plants they feed on.

Control this pest by handpicking the caterpillars. If you have too large a crop for handpicking, you can use a product like Dipel (Bacillus thuringiensis) or Monterey Garden Spray (Spinosad) on the young larvae. Be on the lookout for hornworms with little white “pills” attached. These white attachments are the eggs of the parasitic Braconid Wasp, which feed on and weaken/kill the unsuspecting hornworm. This biological control is a good example of nature keeping everything in balance.

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