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Scouting for Tobacco Hornworms

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Two species of hornworms may be present on tobacco plants, tomato and tobacco hormworms. These species are biologically similar and are managed in the same way.

Hornworm populations may occasionally develop prior to topping, but they are most common post topping in North Carolina.

What part of the plant to scout for tobacco hornworms

Hornworm eggs are round, pale green, and laid on the upper surface of tobacco leaves. Newly hatched larvae are small, appear blueish to pale green with a black horn, and may be on upper surfaces of leaves.

tobacco hornworm egg

John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO,
Creative Commons License licensed under a Creative Commons Attribution-Noncommercial 3.0 License.

Larger hornworm larvae feed within the upper 2/3 of plants, and are often found on the underside of the leaves.

A tobacco hornworm on the underside of a leaf, following the stem of the leaf. Photo: Clyde Sorenson

Tobacco hornworms on the underside of a leaf, following the stem of the leaf. Photo: Clyde Sorenson

How to scout for tobacco hornworms

Hornworms can cause substantial damage to a plant, which is often clearly noticeable. Feeding holes caused by larvae larvae are smooth on the edges and can be very large. Hornworm “frass” or droppings are distinctively barrel-shaped and also indicative of an infestation. Remember, however, that hornworm thresholds are based on insect counts, not damage!

hornworm frass

Whitney Cranshaw, Colorado State University,
Creative Commons License licensed under a Creative Commons Attribution 3.0 License.

Tobacco hornworm thresholds

The hornworm threshold is 1 or more healthy larva per 10 plants, or 10% infestation. Multiple hornworms may be present on a single plants. Five hornworms with parasitic wasp cocoons on their backs are equivalent to one healthy hornworm because they consume approximately 1/5 as much as a healthy, non parasitized larva.

Parasitised hornworm with cocoons protruding from it's sides. Photo: Demetri Tsiolkas

Parasitised hornworm with cocoons protruding from its sides. Photo: Demetri Tsiolkas

Page Last Updated: 10 years ago
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