Depends on how many plants you have and how neat you keep your plants. If you have a hundred overgrown plants then you better spray, if not, chop them up with scissors.

Look for leaf damage and frass (droppings) before you can see the caterpillars. Last year, I found hornworms when they were less than an inch long. Young hornworms eat holes in the middle of the leaves, rather than the edges of the leaves. Look for small holes in the leaves and small black droppings that collect on the leaves below them.

I've heard Bt is good for hornworms, but you have to apply it when the worms are still small. I never use anything other than my fingers though; I pick the worms of as soon as I see them, and bring them inside to rear them (yes, I rear them to adults which will lay more eggs!)

Of course, most people wouldn't want MORE hornworms, so rearing them seems ridiculous when you're trying to save your tomatoes. I guess I've been lucky enough not to have a big enough problem with them, and I like to rear some species of butterflies/moths.

Anyway, try the Bt dust when you suspect there may be baby cats on your tomatoes. I've heard the Bt takes some time before it actually kills the worms, but it will kill them for sure.

I should have mentioned, what I have is 6 potted tomato plants total this year. They are not very large yet but already started producing fruit. They are still small enough that those little buggers did quite a bit of damage to the plant they were on before I found them. It's starting to look like the plants I had last year which looked like sticks with tomatoes hanging off of them. Hopefully it will recover.

Can you give me the full name of BT?

Thanks

Ania

It is called Dipel or Thuricide as brand names. Bonide also sells a liquid form. Hundreds of discussions here on hornworm controls and on Bt in particular that a search will pull up for you to review. There are other brands as well. Just search BT here or on Google.

It's full name is bacillus thurigiensis.

Dave

There are different kinds of BT organisms that produce chemicals which are toxic to different insects.

The BT that we use to kill caterpillars is BT kurstaki. BT israelensis, IIRC, is used to kill mosquito larva in ponds and birdbaths. Those are the ones I've seen most often for non-commercial use.

General info about BT at the link.

Here is a link that might be useful: http://www.nysaes.cornell.edu/ent/biocontrol/pathogens/bacteria.html

Yeah, BT is great stuff. I've never seen my brassicas healthier since I started using it on them -- keeps the cabbage loopers off. It's a bacteria that's highly species-specific. Each variety only affects one order of insects. Var Kurstaki, as missingtheobvious mentioned, is the one you want -- it only kills Lepidoptera (caterpillars, moths, butterflies). And they have to eat it to be killed -- merely landing on it won't do the trick. So unless you spray it on open flowers, you're only going to be killing baddies.

The main downsides to BT are that it doesn't take effect immediately (it takes a day or two after being ingested before the critters stop eating, and longer still before they die) and it only lasts a couple days on the surface of your plants, so you have to reapply it frequently whenever the pests are out.

Bt is great stuff for caterpillars *only* if you apply it before the cats are half-grown.

So, being that you have only 6 potted plants, I suggest you keep a daily watch. Look for the clues already suggested -- frass (aka droppings) that look like small pellets.

I have a lot of peppers too. I think the hornworms attack those as well.

I will keep an eye out and see how it goes just pulling them off and dispatching them for a couple days. I may go get some BT though knowing how bad it can get from last years damage.

Thanks