The Q&A Archives: Tomatoe Horn Worm

Question: I have plum and beefstake tomatoes in my garden. The question I have is where do tomato hornworms come from. I have found two on my plants that had egg sacs on the top of them, what was those sacs from? I'm also having a problem with my leaves turning yellow. Is this from overwatering or nutrient deficiency?

Answer: Tomato hornworms can be 4-5 inches long at maturity, so you may have gotten to them before they were fully grown. Hornworms are the larvae of a large moth (Manduca, with a wingspan of 3 1/2 - 4 1/2 inches). The adult is attracted to tomatoes, eggplant, peppers, potatoes, dill, and various weeds. She lays her eggs on the host plant, the eggs hatch, and the larvae feed and feed. They have voracious appetities and can denude a tomato plant in a day! The worms with white cocoon like sacs have become hosts for the beneficial braconid wasp. The sacs contain eggs of the wasp which will hatch and destroy the caterpillar. Leave these caterpillars alone so the wasps can do them in. You can destroy those worms without white cocoons. Handpicking is the best defense. You can use the botanical Bt (Bacillus Thuringiensis), which is a bacterium that acts as a stomach poison, and is quite effective against most caterpillars. To keep hornworms away from your tomato plants next year, try interplanting dill. (Hornworms like dill and are easier to see and remove on the wispy dill foliage.)

Yellowing leaves can be a symptom of overwatering or lack of nutrients.

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