This large caterpillar can eat a great many leaves in a single day and is a major pest. Having said that – you don’t spray for this one. You patiently look the plant over – starting with the branches with the least amount of damage (they’re usually the most recent although not always). And you look under the stems.
How do you find them?
You’re going to have to take your time with this one. Start at a damaged area and track the leaf stem back to the main stem. Watch the undersides of the stems/leaves as that’s where they normally are. They eat from the bottom.
I often kneel down beside the plant and look slightly upwards as I track back from the end of each damaged stem to pick them out. They’re not easy to see unless you take your time. And it’s a question of practice. The first few times you try to find them, they’ll be harder to pick out but once you learn to look for that distinctive “bump” on the underside of a leaf/stem that shouldn’t be there, it will become easier.
When you see one, you kill it. You can do it in any way you like – from stomping to dropping in a pail of soapy water. I pull them off the stem but they grab on hard (wouldn’t you if you were about to be dropped into a bowl of soapy water?) 🙂 and it’s often easier and “less gross” to snip off the branch they’re on and drop the entire branch into the pail.
I sometimes get asked, “Why don’t you just spray?”. Bt will work on hornworms but it’s not available on the home scale in Canada. You have to hit them with soap to “kill them” and there are two problems with this. The first is that it’s tough to hit them on the underside of the leaf and the second is that it doesn’t kill them – it just makes them cleaner. Diatomaceous earth works nicely if you coat the entire plant with it.
Some gardeners recommend carrying a pail of soapy water. I don’t carry a pail with me but drag my heel to make a furrow in the garden, drop the caterpillar into the trench, cover it back over and step on it. The soil microorganisms will thank you for dinner and recycling is a good thing.
ADULT FORM OF THE TOMATO HORNWORM
The adult form of this insect is a grey brown Hawk Moth and those with wildlife gardens can plant a tomato in the back in order to support this amazing creature. You won’t get many tomatoes from it but you may see a hovering hawk moth instead.