Q: We have several different types of trees in our yard that have for the past three to four years been infiltrated by those large green hornworms.Β It is a complete puzzle to us where they come from, as we have no tomato plants or vegetable garden of any kind, and also why they keep showing up every year.
My husband has sprayed the trees with a solution that usually causes the worms to fall to the ground and thereby easy to find and dispose of, but why are we having this problem year after year and what can we do to avoid it? The trees we find them in are ash and willow. Any advice you can give would be appreciated.
A: The hornworm caterpillars you are finding are related to the tomato hornworm but not necessarily the same species.Β Tomato hornworms feed on potato, tobacco, tomato, and other plants in the nightshade family (Solanaceae). Other species of hornworms will feed on other plants such as your trees.
The sphinx or hawk moth family (Sphingidae) to which the hornworms belong includes about 125 species in North America. Around 40 or so of these can be found in Pima County. They are called hornworms due to the conspicuous horn on the back end of their abdomen and that is a clue that helps identify them as members of this family.
The adult moths, which are excellent flyers, lay eggs on their host plants, often at night. These caterpillars are not considered to be pests on trees since trees can handle some defoliation without any adverse affects. The caterpillars are also a good food source for birds so you can leave the pest management to them and save yourself some time and money on the insecticides.
Plus, I am guessing you donβt want the birds to eat caterpillars laced with insecticides. There is no practical way to avoid this situation in the future. You like your trees and the caterpillars have to eat.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed toΒ tucsongardensage@gmail.com
