Hornworms and Tomatoes

When I hear the phrase “tomato pest,” the next term which comes to mind is “hornworm.” There are a number of insect pests which bother tomatoes, but I can’t think of any other which is as “spectacular” as the hornworm.

Tomato hornworms are usually hard to spot.

A “newbie” may struggle to find them, as they camouflage extremely well. They blend in and look like nothing more than a slight thickening of the tomato’s stem. As a boy, I learned to look, not so much for the worm, as for its poop. These critters are voracious eaters of tomato leaves, stems and fruit, and as they eat they make lots of poop. Their poop looks like moist greenish little pellets, often sticking to leaves below them.

hornworm damage
Hornworms typically denude the leaves and small sprouts from the tomato’s branches.

Stubby looking branches without leaves are a dead giveaway that a hornworm has been at work. When you find this, start looking for the worm and for its poop. With some years of experience one can train their eyes to spot them quickly.

One can also use a black light to find hornworms, after dark. This works really well!

I have a friend who is a market gardener who swears by this technique.

Some hornworms which eat tomato plants aren’t really “tomato” hornworms.

There are a couple of different species of hornworm. One of the most troublesome for tomato growers is the tobacco hornworm. Frankly, I don’t worry about which is which. If it’s big, fat and eats tomato plants, I need to deal with it!

How can I control hornworms?

tomatoes with insecticide on them, pesticide treated tomatoes, tomatoes with seven on skin

I do not recommend insecticides and here’s why. Besides, who wants to spray poison on their food?!

Most often I simply hand pick them from my plants. (No, they don’t bite.) Most years we only get a few, so I don’t care to do anything costly or really involved. I simply hand pick them and… feed them to our ducks. Our ducks love them. Bacillus thuringiensis (Bt) is a naturally occurring bacteria which can be purchased and used to kill hornworms. It’s definitely safe for humans. The downside of Bt is cost and that it will also kill almost any caterpillar. I much prefer to hand pick. Finally, there is a kind of wasp called a Braconid wasp, which parasitizes and kills hornworms. These are very effective, and I know there was once a way to purchase them. I simply wait until I spot a parasitized hornworm, and leave it alone, letting the little wasp larvae hatch and complete their life cycle. Gardeners up North probably can’t count on these wasps showing up on their own.

 tomato hornworm, Braconid wasp larvae
Tobacco Hornworm with parasitic wasp eggs
by: Paul VanDerWerf
Creative Commons License:
https://creativecommons.org/licenses/by/4.0/

If you should see a hornworm covered in little white cocoons, leave it alone! That worm will not harm your plants, as it is already paralyzed. The wasp larvae will hatch out and repeat the cycle, saving you both time and, possibly money!

Blossom End Rot is another common tomato problem.

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