By Lee Oliphant
I carefully selected disease resistant tomato plants this year and they look healthy. But something is chewing on leaves and fruit. What is it, and what can I do about it? Katie, Cambria.
It is difficult to know what is doing damage to your tomato plants unless you catch the pesky critter in the act. Some damaging invertebrates include sucking insects such as aphids, thrips, whiteflies, and tomato russet mites. When there is evidence of chewing as you describe, it is most likely caused by flea beetles, loopers, or the westerns spotted cucumber beetle. Hornworm and the tomato fruitworm can damage both leaves and fruits. Snails and slugs also dine on tomato plants and fruits. Be observant during the daytime and use a flashlight in the evening to try to identify the culprit.
The University of California lists over 20 invertebrates that feed on tomato leaves and fruits on the UC Integrated Pest Management (IPM) website: http://ipm.ucanr.edu/PMG/GARDEN/VEGES/tomato.html. The site describes each insect, its eating pattern, and how you can safely manage it in your garden.
Most authorities do not recommend spraying insecticides in home vegetable gardens. Insects can be hand-picked from the leaves and put in a bucket of soapy water. Hornworms, a common pest of tomato plants, are large green caterpillars with a rear prong that looks like a horn. They are the larvae of the sphinx moth, a nighttime pollinator. Tomato fruitworms are small green or brown-striped caterpillars that eat the leaves and the fruit of tomatoes. You may also have seen them inside the husks of corn, dining on tender kernels.
Practice good IPM methods of control and you'll have few problems with pests on tomatoes. Let predators, parasites, pathogens, and competitors control pests. Reduce pest establishment, reproduction, and dispersal through good gardening practices like keeping your garden clean. When possible, use traps (like yellow sticky strips), instead of sprays. Pesticides are recommended only when needed and in combination with other approaches for more effective, long-term control. Pesticides should be selected and applied carefully and in a way that minimizes their possible harm to people, non-target organisms, and the environment. Regardless of unwelcome visitors, home-grown tomatoes are worth the effort!