Hi, Kirsten - I'm kinda the moth person here, having raised both the tomato and tobacco hornworms. Did your caterpillar have a red or black horn? These are distinguishing factors between the two manduca species. Tomato hornworms have a black horn, and tobacco hornworms have a red horn. Both consume plants in the solonaceae family (tomato is a member of this family).

Things like day length and temperature both play into time of emergence. Are you in northern California where it gets relatively cold, or southern California? If southern, it may emerge before springtime because your zone does not get as cold.

Susan

I was just outside looking over my tomato plants. All the fruits get a single little hole bored in them by something. Then I spotted an inch long green spagetti like caterpillar. It was just dumb luck I saw it at all as it was the same color as the tomato plants. Then I started trying to untangle my tomato plants as they had grown into a big mess. It was then that I stood back staring at what I saw. It was the caterpillars mommy! Wow, 3 inches long, same green color but with symetrically patterned white strips, black tiny dots to the sides of the white stripes and one mean looking reddish horn-like thing near the end of its back. And fat as could be on my tomatos. Kinda pretty but I wonder how many more are out there on my plants.

So it's a tobacco hornworm eh?

Can I treat the plants with anything organic to get rid of them?

Hank,

You can treat your plants with Bt, which is Bacillus thuringensis, variety kurstaki, which is a naturally occurring bacteria. It is found in products labeled as caterpillar killers and can be purchased either as a powder or liquid.

The kurstaki strain of Bt kills not only tomato hornworms, but also other garden pests like cabbage worms, cabbage loopers, European corn borers, corn earworms and tomato fruitworms (which I think are the same worm), and both spring and fall cankerworms. There are other forms of Bt available, including the San Diego strain, which kills Colorado potato beetles and the Isralensis strain, which kills mosquito larvae, fungas gnats and black flies.

The downside to using the Bt kurstaki caterpillar killer is that it will kill ALL the butterflies and moths, not just the undesirable ones. For that reason, many people no longer use it. I haven't used it for years, now, since I prefer to have the butterflies and moths around me in the garden.

The fall is an especially bad time to use Bt, as the monarchs are migrating through our state at this time, and the use of Bt threatens their existence.

I have been out in the garden a lot the last few weeks, and it is full of all kinds of moths and butterflies, including the sphinx moths for whom hornworms are the larvae. In a garden that has 40 or so tomato plants still healthy and producing tomatoes, I have seen hornworm damage on only one plant.

Do I like seeing hornworm damage on my tomato plants and fruits? No, absolutely not. However, I tolerate the damage because I love the moths. In fact, I plant other plants like datura, four o'clocks, moonvines, and nicotine specifically FOR the moths.

If the hornworms are doing what you consider unacceptable damage, you can pick them off the plants and squish them.
Bt works, obviously, but the tradeoff is that it will kill all the butterflies and moths exposed to it. Your choice.

Dawn

I grow extra tomato plants I don't count on harvesting tomatoes off of just for the hornworms. They are isolated from the others and any hornworms that show up on my plants get moved to their plants.

randy

I'd pick the worms off if I could see them. Only reason I saw the big one I did was because it was on a stalk where I could see it. Had it been on the other side of that stalk I never would have found it. And the little one was just luck as I was picking a fruit it was getting ready to eat.

Hank

Hank,

They can be hard to see. I usually don't notice them until they have stripped a few branches on a tomato plant.

Randy,

Some years I plant 'extra' or 'leftover' tomato plants specifically for the hornworms, and when I do that, I also move the hornworms to those plants. This year the 'extra' plants were near the garage/barn and they actually performed better than those in the regular garden plot, presumably because they were on higher ground during the heavy May-July rains.

However, I have so many birds in the garden that most caterpillars don't stand a chance anyway, so I see very little hornworm damage on the tomatoes themselves. If I had to guess, I'd say I lost less than a dozen fruit to hornworms this entire year, and I had hundreds of tomatoes, so a dozen or so is just a drop in the bucket.

We seem to have fewer hornworms in the yard/garden/pasture this year, but lots more grasshoppers and crickets than usual.

Dawn

You can make tomato hornworms reveal themselves by spraying the plants with a very fine mist of water. The hormworms will make an audible "click" sound and rear up halfway off of the stem they are on in a defensive posture. I find them this way but since I learned that they are the larvae of the sphinx moth, I no longer kill them but do like Dawn and RAndy and move them to a "spare" plant, usually the earliest variety in the garden which we stop eating when the main varieties come in. But not many remain; I suspect the birds get them too. Dorothy