Scouting for Tobacco Hornworms
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Collapse ▲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.
John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org
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.
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!
Whitney Cranshaw, Colorado State University, Bugwood.org
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 its sides. Photo: Demetri Tsiolkas