Hornworms

Hornworms can be pests of tomato and pepper in field grown crops, but for some reason seem to be

Figure 1. Hornworm feeding on tomato leaves in a high tunnel.

Figure 1. Hornworm feeding on tomato leaves in a high tunnel (photo by Wenjing Guan).

particularly severe in high tunnels. Hornworms are very large caterpillars, measuring up to 4 inches long (Figure 1), and they can consume large quantities of foliage and will also feed on green fruit (Figure 2). In fields, hornworm damage is usually localized and tolerable, although treatment is sometimes required. In high tunnels, hornworm damage, particularly to tomato, is often severe (Figure 3) and will require several applications of insecticides. In field situations, the treatment threshold is one hornworm per two plants. Since the infestations are often localized, it may not be necessary to treat the entire field. In high tunnels, there is no established threshold, so my recommendation would be to treat as soon as you seen caterpillars or their damage. The good news is that hornworms are fairly easy to control. The list of recommended insecticides can be found on pages 137-8 of the Midwest Vegetable Production Guide which can be found at https://ag.purdue.edu/btny/midwest-vegetable-guide/Pages/default.aspx. Not all of these products can be used in high tunnels. See page 42 of the guide for the list of insecticides allowed for use in high tunnels.

Figure 2. Green tomato fruit damaged by hornworm (photo credit: Wenjing Guan)

Figure 2. Green tomato fruit damaged by hornworm (photo by Wenjing Guan)

Figure 3. Severe hornworm damage on tomatoes in a high tunnel (photo credit: Wenjing Guan)

Figure 3. Severe hornworm damage on tomatoes in a high tunnel (photo by Wenjing Guan)

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