Garden Detective: Looking for tomato hornworms? Try black light

Readers continue to chime in on tomato hornworms, including this handy trick for tracking the critters.

“The article about tomato hornworms on Nov. 16 mentions picking them off the tomato plants to destroy them. It does not mention how hard it is to see the critters in among the tomato leaves,” said Dr. Richard Buss of Jackson. “I found that they glow under an ultraviolet black light if you look for them after dark.”

The black light works where the naked eye cannot see the big, green worms, which tend to blend in with their surroundings.

“One day I searched for about 20 minutes and found only four worms on my tomato plants,” he said. “That night, I went out with the black light and found about 20 more!

“Finding that you even have an infestation with tomato hornworms can be hard, until you see your plants stripped of leaves. If you look for the droppings on the ground, which look like little black pills, you can get a jump on them. Then get out your black light and go worm hunting.”

Where to get a black light? “Black light flashlights can be purchased on eBay, or you can get an ultraviolet bulb for a fluorescent desk lamp,” Buss suggested.

Buss is on a one-gardener crusade to teach more bug hunters about the wonder of black lights.

“I have tried to alert the world about this trick,” he said. “I wrote to Mother Earth News about 10 years ago, and they printed my letter. I put it in the Wikipedia article about tomato hornworms, but it has since been modified. But Wikipedia now has a picture of a tomato hornworm glowing under ultraviolet.”

Now for the answer to another mystery. The photo of a larva that ran with the original article Nov. 16 was not a tomato hornworm, as alert readers have pointed out. But what was it? Another kind of tomato pest.

“Your picture of a ‘tomato hornworm’ in the Nov. 16 paper isn’t – it has no horn!” noted Art Shapiro, a professor in the Department of Evolution and Ecology at UC Davis. “It’s the tomato fruitworm, Heliothis zea; a very different bug in a different family – Noctuidae.”

With recent freezing weather, the tomato worms – along with tomatoes – have vanished. But keep an eye out for the pupae hibernating in mulch. If you see them, dispose of them, or you’ll have more worms next spring.