Gardening questions don’t arise just once, then disappear forever, especially when they involve insect pests or suspected plant diseases. A request from the Gloucester Extension office last week to respond to a query from a county resident about tobacco hornworms on tomato plants sent me back to a 2017 column and a photo, sent to me by fellow Master Gardener Bonnie Bernard, of a large, pale-green caterpillar covered with bizarre projections that looked like grains of rice.

This caterpillar and its cousin are the bane of tomato and tobacco growers. It is a hornworm, and it loves tomato plants. It isn’t crucial for the home gardener to distinguish a tomato hornworm from a tobacco hornworm. This one happens to be the tobacco hornworm (Manduca sexta), recognizable by the red horn on its rear end. The tomato hornworm (Manduca quinquemaculata) has a black horn. Both species are yellow-green in color with seven pairs of diagonal lines along the sides. They can reach 4 inches in length. Ho...