Question:
Last year, I encountered more Tomato Hornworms than ever before. I control them by picking them off; however, are there other methods for managing them? Additionally, what do they transform into, if anything?Answer:
- The Tomato Hornworm is the larval stage of the Sphinx or Hummingbird Moth.
- Its life cycle consists of four stages. It begins when the adult female moth lays round, pale green eggs on the leaves of tomatoes. These eggs hatch into small green caterpillars that have a horn-like structure on their backside.
- In the second stage, the caterpillars grow large, reaching up to four inches in length, with one purpose: to eat continuously, twenty-four hours a day. As a result, they cause significant damage in a short period. They feed throughout the summer before entering the third stage of their metamorphosis, the pupal stage.
- The pupae drop to the ground in September, forming a hard brown shell structure. This shell has a narrow tongue that protrudes, resembling a handle on a pitcher, making it easy to identify.
- While underground, the pupae develop into adult moths, completing the fourth stage of their life cycle. In late May or early June, the adult moths emerge from the ground to start the cycle all over again. In addition to hand-picking the caterpillars off the plants, several environmentally friendly methods exist to control Hornworm populations.
- Due to issues from the previous year, I first applied beneficial nematodes to the soil to target the pupae. This treatment isn’t always necessary.
- Beneficial nematodes are tiny, worm-like organisms that hunt and destroy soil pests, including Tomato Hornworm pupae and grubs, while leaving earthworms unharmed.
- They can be found at your local garden center, alongside other beneficial insects like ladybugs and praying mantises.
- Hornworms typically appear in late June or early July, so be vigilant. Early on, they tend to be found toward the center of the plant, primarily on the undersides of the leaves. Look for any chewed leaves, large holes, or black droppings around the base of the plants.
- Two environmentally friendly pesticides that can help control Hornworms are Captain Jack’s Dead Bug Brew and Bacillus thuringiensis, commonly known as Bt. You must make repeat applications every three weeks, as multiple infestations can occur during the ‘Worm Season,’ June through September. This includes Budworm on Geraniums, Petunias, and Nicotiana. The adult moths can fly in from surrounding areas.
- BT is specific to caterpillars and causes them to develop a lethal case of stomach flu. The caterpillars will continue to feed for a while before exhibiting symptoms, which will contribute to further damage. It’s advisable to wait several days for this control to take effect.
- Captain Jack’s Dead Bug Brew is a broad-spectrum pesticide that kills on contact and through ingestion. It is the preferred choice if you need immediate control. I recommend manually removing the worms until the population increases, then spraying with Captain Jack’s Dead Bug Brew.