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How to attack pesky critters damaging your tomato plants

A tomato fruitworm dines on a ripening tomato.
A tomato fruitworm dines on a ripening tomato.

Q. I carefully selected disease-resistant tomato plants this year and they look healthy. But something is chewing on the leaves and fruit. What is it, and what can I do about it?

Katie, Cambria

A. It is difficult to know what is damaging 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 more than 20 invertebrates that feed on tomato leaves and fruits on the UC Integrated Pest Management website: www.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 tomatoes’ leaves and fruit. You may also have seen them inside the husks of corn, dining on tender kernels.

Practice good pest management methods and gardening practices, such as keeping your garden clean, and you’ll have few problems with pests on tomatoes. Let predators, parasites, pathogens and competitors control pests.

When possible, use traps such as yellow sticky strips instead of sprays. Pesticides are recommended only when needed and combined with other approaches for more effective, long-term control. Select and apply pesticides carefully and in a way that minimizes their possible harm to people and the environment.

Regardless of unwelcome visitors, homegrown tomatoes are worth the effort!

Lee Oliphant is a UCCE Master Gardener.

Got a gardening question?

In San Luis Obispo call 805-781-5939, Arroyo Grande, 805-473-7190 and Templeton, 805-434-4105. Visit us at http://ucanr.org/sites/mgslo/ or email us at anrmgslo@ucanr.edu. Follow us on Instagram at slo_mgs and like us on Facebook. Informative garden workshops are held the third Saturday of every month, 10 a.m. to noon at 2156 Sierra Way, San Luis Obispo. Garden docents are available after the workshop until 1 p.m. To request a tour of the garden, call 805-781-5939.