Hornworm ( Manduca spp. ) - Ask Extension
How do I get rid of tomato horn worms this growing season? How do I get rid of them permanently?
My tomato plants have been attacked by horn w...
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Hornworm ( Manduca spp. ) #875252
Asked June 29, 2024, 2:43 PM EDT
How do I get rid of tomato horn worms this growing season? How do I get rid of them permanently?
My tomato plants have been attacked by horn worms. These are caterpillar insects that are almost the same color as the plant and can range in size from barely visible to 3 inches log. I am not sure but I think that they hatch from eggs in the dirt or clinging to the under side of plant leafs. I think that the eggs look like tiny black dots. When eating the plant they leave droppings of small black balls. I know to pull the visible insects of of the plant and crush or drown them but I do not know how to get rid of the tiny ones and the eggs. What should I do? If I spray the plants with a forcefull spray of water from a garden hose will that knock the tiny insects and the eggs off of the plants and kill them? Is there an insecticide that will kill them? How do I find their eggs in the ground?
This is the second year that I have had this problem. If I leave this area of the garden fallow next year will that eliminate them for 2026 and beyond? Is thers another way to get rid of them for 2025 and still plant tomatos in the same area?
Charles County Maryland
Expert Response
Tobacco Hornworms (the caterpillar more common than Tomato Hornworms on tomato, though that nuance doesn't matter much here) generally do not cause serious damage to tomatoes before they are old enough to spot and remove by hand. (Or the parasitoid wasps will beat you to it, which are good to have around.) The black pellets are frass (insect poop), and their size will correspond to the size/age of the caterpillar. Tiny frass comes from young caterpillars (or just other insects), and large frass comes from large caterpillars. The eggs are not readily visible because they blend in well, being laid on foliage and are small, round, and green. (They are not laid into soil...the only part of the life stage of these insects which does shelter in soil is the pupa.) Our web page Tobacco or Tomato Hornworm on Vegetables provides more detail about the life cycle and management options.
There is no way to permanently exclude them, as moths can always fly back into the area (and leaving a bed fallow won't help much either for that reason), but covering plants until they start to bloom with insect mesh netting can prevent moth visits for a time. (Since bees should be able to pollinate the flowers, it's best to uncover the plants once flowering starts.) Spraying with a garden hose can certainly knock some pests off of a plant, but in this case, it probably won't be enough force to be successful.
Miri
There is no way to permanently exclude them, as moths can always fly back into the area (and leaving a bed fallow won't help much either for that reason), but covering plants until they start to bloom with insect mesh netting can prevent moth visits for a time. (Since bees should be able to pollinate the flowers, it's best to uncover the plants once flowering starts.) Spraying with a garden hose can certainly knock some pests off of a plant, but in this case, it probably won't be enough force to be successful.
Miri
