Dealing with Hornworms in the Garden

If you’ve gardened before, especially if you’ve ever grown tomatoes, you are likely familiar with that green grinch of the garden, the tomato hornworm. The hornworm (manduca quinquemaculata), is actually the larval stage of a family of hawk moths that include the Sphinx and Hummingbird moth, of the family sphingidae.

The hornworm derives its name from the distinct hook-like horn protruding from its posterior. These hooks are often mistaken for stingers, but in truth, are harmless.

Fascinating little creatures resembling a hummingbird when mature, they are destructive little devils during their multi-stage transformation into caterpillars.

Hard to Spot

Hornworms are masters of camouflage. Although more than four-inches long, their near perfect color-match of your green tomato vines affords them virtual invisibility. You really have to look carefully to see them. Once you do though, it’s almost an aha! moment. But don’t limit your inspection to just tomato plants. These worms also feed upon potatoes, peppers, and eggplants, and can defoliate a plant rather quickly.

Though you may not see a hornworm, look for tell-tale signs revealing their presence. Check any leaves beginning to droop or vines that appear stripped of leaves. Take the time to look your plants over thoroughly because once laid, their eggs hatch quickly, usually within four to five days. Once hatched, these newbies are voracious and destructive eaters. Careful inspection can be the difference between a good harvest and a good cry.

All in the Family

The tomato hornworm isn’t alone when it comes to eating plants and dreams. Its cousin, the tobacco hornworm (manduca sexta), can be just as devastating to its namesake, the tobacco plant. Strangely, both are drawn to plants of the Nightshade family to include tomatoes, green peppers, tobacco, eggplants, and potatoes. So, you may find a tobacco hornworm on a tomato plant and vice versa.

Read also: Nine Vegetable-eating Insects that will Kill Your Garden

While quite similar in looks, the tomato and tobacco hornworms are distinguishable. The tomato hornworm sports a set of white, v-shaped markings along its sides with a black horn on its tail end. The tobacco hornworm displays vertical white lines with a red-colored hook adorning its back bumper.

The pneumonic I use to remember which-worm-is-which is associating the v-shaped markings of the tomato hornworm with V-8 Juice, made from tomatoes.

Both insects pupate underground over the winter months and emerge as moths in the spring. Time is of the essence and reproduction is numero uno on their bucket list. After breeding, the female deposits her eggs on the verso of the leaf. When they hatch, the next four weeks are spent feeding on your plants until reaching maturity, at which time they drop back into the earth to pupate and reset the cycle.

Plant Friendly Hornworm Pest Control

Gardeners wishing to avoid potentially dangerous chemicals have some effective options. Here are some simple home-style remedies for dealing with hornworms.

The simplest time-tested method to rid your plant(s) of tomato hornworms is the hands-on/bugs-off approach. It’s as uncomplicated as it sounds. You manually pluck the hornworm off your plants with gloved fingers. Some use water to blast them off but you run the risk of damaging the plant and besides, it’s so messy.

Read also: Getting Rid Of Bad Bugs with Beneficial Insects

Regardless of method, once removed, you can free-fall the little critter into a container of water and effectively drown him, or simply drop him to the ground and do your best Bigfoot impression.

Spraying Your Tomatoes

Another deterrent to the hornworm and other garden pests is to make up a sprayable solution from a base of biodegradable, liquid dish soap. There are no set-proportions for the recipe. Just add water to a little soap until it’s somewhat soapy then sprinkle in some cayenne powder/pepper. Spray your plants down with this solution. The soap helps the pepper-laden elixir stick to the plant.

This has proven to be an effective treatment. Many garden pests are repelled by the smell and taste of this concoction. As an added benefit, this potion won’t harm your plants. Reapply as needed.

Note: Should you discover a hornworm with a cluster of white eggs attached to its back, give thanks. Those eggs are not the eggs of the hornworm but of a garden-friendly parasitic wasp (Braconid Wasp) that lays its eggs on the back of the caterpillar. When those eggs hatch, it’s role reversal. The wasp larvae become the diners and the hornworm becomes the dinner.

Not to mention you’ll soon have a little army of wasps (harmless to people) that feed on the tomato/tobacco hornworm larvae while helping defend your garden against other harmful insects.

For additional protection, place sheets of plastic on your garden floor. This will help prevent the moth from breaking through the ground come spring. This is also effective weed control.

Nature vs Nature

Other methods of combating hornworms include the use of pesticides. But good ones. Bacillus thuringiensis, or BT as it is also known, is a safe biological pesticide or living organism. It is a soil-dwelling bacterium that kills a variety of garden pests including hornworms. Another perquisite, BT is harmless to vegetation.

Read also: Bacillus Thuringiensis in Horticulture

BT begins to work after an insect has eaten a leaf from the treated plant. Once ingested, a specific protein is produced that causes the insect to completely lose its appetite. We all know what happens when you don’t eat. BT can be readily purchased wherever gardening supplies are sold and even online. Begin treatment early or at the first sign of leaf damage.

And there you have it. With a bit of discipline and a little help from Mother Nature, you too can enjoy a healthy tomato/garden harvest and go from having a little green worm to a big green thumb!