Daily Local News (West Chester, PA)
The big, the bad, and the hungry
Several weeks ago I got an email message from my friend Diana, who also lives in Kimberton and is a bit of a plant geek in her own right. We’ve shared a lot of gardening triumphs and failures with each other. This time Diana had a tale of woe. “Thought I’d let you know I’m going to put up my deer fencing this evening. Some deer walked up the back steps to my deck and ate the upper leaves/blossoms of my tomato plant last night! The browse marks are typical deer and that’s the only animal that is tall enough to get at something four feet high. We will see baif it works.”
An update came three days later, but it wasn’t what I expected. “Well,” reported Diana, “the local deer are off the hook as far as my current decimated tomato plant is concerned. I noticed droppings under the plant this morning, and with the rope across the deck stairs for the last two nights (I didn’t totally trust the deer-proofing fencing) I took a really close look at my plant. I finally saw a tomato hornworm (really big). The darned thing has (had!) eaten every top leaf, all the flowers, and several tomatoes. Big lesson.”
Actually, the important part of this story is this one sentence: “I took a really close look at my plant.” Most insects are small, many are exceptionally wellcamouflaged, and they’re also good at hiding. For preventing the kind of damage that Diana experienced, physically check your food plants at least once a week, if not more. Turn over leaves. And look not only for insects but also for their eggs.
Tomato hornworms (Manduca quinquemaculata) are quite large — up to four inches long and as thick as a finger — but their color blends exactly with the color of tomato plants. You often have to “look with your hands” as well as your eyes, looking throughout the entire plant, to detect them. Defoliation, often toward the top of the plant, is a good give-away. As Diana did, you may also find dark-colored droppings, called frass, below the plant or on lower leaves. Once you find the caterpillars, control is easy: just pick them off and squish them or dispose of them by some other means. Earlier in the season, with a close eye, you may be able to detect the tiny, single, lime-green eggs.
According to the Denver, Colorado Cooperative Extension Office, tomato hornworms avoid direct sunlight, tending to “feed on the interior of the plant during the day and are more easily spotted when they move to the outside of the plant at dawn and dusk.”
The tomato hornworm is the larval stage of the Five-spotted Hawk Moth. Despite the exotic-sounding name, this moth
is drab and insignificant-looking except for a row of yellow dots on either side of its body. The larva feeds primarily on tomato plants, but also on the other members of the Nightshade Family: potatoes, peppers, eggplant, and tobacco.
If you find a hornworm with little white ovals attached to its back, ovals that look like mini cotton-swab tips, that’s a good sign. These white ovals are the eggs of the braconid wasp, which is a parasite of the tomato hornworm.
The wasp lays its eggs inside the hornworm. When the eggs hatch, the larvae begin feeding on the insides of the caterpillar and eventually pop out on the skin as tiny, white cocoons. I’ve counted between 40 and
50 cocoons on the back of a single caterpillar.
By the time the cocoons are evident, the hornworm is pretty much done for. So it makes no sense to remove the caterpillars at this point. Rather, it is better to let the wasps continue their life cycle, thereby insuring continuing protection from hornworms.
Pam Baxter is an avid organic vegetable gardener who lives in Kimberton. Direct e-mail to pcbaxter@ verizon.net, or send mail to P.O. Box 80, Kimberton, PA 19442. Join the conversation at “Chester County Roots,” a Facebook page for gardeners in the Delaware Valley. Go to Facebook, search for Chester County Roots, and “like” the page. To receive notice of updates, click or hover on “Liked” to set your preferences.