Horn worms are best controlled by carefully inspecting your plants are removing them by hand. They're pretty good at hiding, aren't they? ;-) If you happen upon any with a crop of little white 'cocoons' all over them, leave them be. They have been parasitized by a teensy wasp, and you want to have plenty of those around your tomato plants.

spray with BT for caterpillers, but if they have the little white cocoons on them leave them alone because nature is going to get rid of them for you...:)

kendra

And if you will do a search here using "tomato hornworms" you can learn a great deal more about them (they come every year). There are many discussions about them, some on this page now that you know their name. You can see several photos and also see a picture and details on why the ones with the white cocoons on their backs need to be left alone. Lots of info!

Dave