Connecticut Garden Journal: Spotting Tomato Hornworms
They're back!!! Every year at this time I start searching for the tomato hornworm. It's not hard to see the damage. These caterpillars of the hawk moth start out small on the tops of tomato plants. As they eat, they grow and turn into 4 to 6-inch long monsters! Well, maybe they aren't that scary, but they can cause lots of damage on leaves and fruits.
Once you start seeing some munching of the leaves, start looking for the caterpillars. I look for the dark green, droppings as a sign of their arrival. When you find the droppings on lower leaves, look up. Chances are there's a tomato hornworm right there. Although they're big, their colors camouflage them perfectly among the tomato leaves. Every morning we go hornworm hunting dropping them into a pail of soapy water. You can also feed them to chickens.
If you still can't seem to find the hornworms doing the damage, try going out at night with a black light. The tomato hornworm caterpillars will glow and become very evident.
For big patches of tomatoes you might have to resort to Bacillus thuringiensis or Bt spray. This bacteria kills larvae in the moth/caterpillar families including hornworms. Coat both sides of the leaves with spray and in a few days they'll start dying. Be careful not to spray other plants as Bt will kill all caterpillars, even good ones. If you find tomato hornworms with white protrusions on their back, leave them. That's the cocoon or pupa stage of a braconid wasp that is parasitizing your hornworm. These a good guys in your garden.