Few things stir a gardener’s soul like the sight of juicy, red tomatoes ripening on the vine.
And few things harden that soul like the discovery that someone — or something — helped themselves to that late summer bounty, decimating the crop.
“Things will be going along great,” Jim Dill, pest management specialist with University of Maine Cooperative Extension, said. “Then all of a sudden it’s like, what happened to my tomato plants?”
If the evidence presents as chewed or missing leaves, denuded stems or holes in the tomatoes, the culprit is likely the “tomato” or “tobacco” hornworm [Manduca sexta] the caterpillar stage of the sphinx moth, according to Dill.
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Just ask Meg Haskell, who two summers ago found herself battling the garden pest.
“They wreaked havoc on my tomatoes in short order,” Haskell recalled. “They did just a ton of damage.”
Haskell said she had been away from her Stockton Springs home for a few days, and when she returned home she discovered all was not well in the garden.
“We had been paying extra attention to our tomato crop,” she said. “We had this big, beautiful pack of plants begging to bear fruit, [but] when I went out to look at them you could tell from 15-feet away something was wrong.”
In her absence, the hornworms had apparently decided both the time and tomatoes were ripe for an invasion
Haskell described seeing her once-vibrant plants looking bedraggled, stems chewed and the tomatoes that had begun to set gnawed upon.
“That’s what happens,” Dill said. “It’s when they have reached the stage of having voracious appetites that you first see hornworms.”
Scientifically, in the hornworm life cycle, it’s the final instar larval stage, according to Dill, and tomatoes are their food of choice.
Earlier in the summer an adult Sphinx Moth had laid her eggs and, after hatching five days earlier, the caterpillar larvae has grown from a half-inch to up to 4 inches long.
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When the caterpillar is around 5- or 6 days old, it drops off the tomato plant and burrows underground, where it will spend the winter in the pupa stage before emerging next spring as the Sphinx Moth.
The hornworms’ bright green coloration and striped body do give it a sort of beauty, Dill said, but it also acts as a great camouflage.
“They really blend in so can be difficult to see and find on tomato plants,” he said. “I tell people to start looking for frass.”
Frass is the scientific term for insect larvae poop and looks like brown cubes with the end points sanded off.
“If you start seeing frass you need to start looking hard at your plants and removing any worms you see,” Dill said. “Early on they will be quite small but then all of a sudden you see the really large ones.”
For Haskell, who’s been gardening in Maine for 30 years, it was her first experience with hornworms.
Since an infestation of hungry hornworms are capable of decimating a tomato patch in short order, immediate action is needed, which is exactly what Haskell said she did.
“I filled a mason jar with soapy water and went back out and started upping them off the plants,” she said. “We had maybe six plants, and there were hornworms everywhere. I filled the jar.”
The soapy liquid is fatal to the worms and one way to get rid of them.
Dill said gardeners can also pluck the worms and toss them as far away from the plants as possible.
“It’s sort of like catching a woodchuck and relocating it,” Dill said. “They won’t find their way back to the plants.”
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Dill said he’s also heard the hornworms make excellent fishing bait.
Hornworms don’t have natural predators but are hosts for a parasitic wasp that will lay its own eggs on the living caterpillar. When those eggs hatch, the wasp larvae feed on the hornworm, eventually killing it.
They are not dangerous to humans, Dill said, decimated gardens notwithstanding.
Haskell, who did say her tomatoes of two years ago did recover from the hornworm attack and bear fruit, is now on constant watch.
“We’ve not had any since that infestation,” she said. “I’m keeping a close eye out for them because I don’t ever want to see them again and I know what I’m looking for.”
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