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How to save your plants from the destructive green spotted beetle

The spotted cucumber beetle likes cool coastal climates.
The spotted cucumber beetle likes cool coastal climates.

Q: I’ve begun seeing insects in my garden that look like little green ladybugs. They’re eating flower petals and leaves. What can I do to get rid of them?

Carol G., Cambria

A: Except for its shape and size, the yellow-green western spotted cucumber beetle (Diabrotica undecimpunctata) is not related to the red “ladybug” or lady beetle (of “Fly Away Home” fame).

The spotted cucumber beetle is a destructive insect that feeds on plants and crops, especially in cool coastal climates. Even its larva is considered a pest as they feed on the plant roots before taking to the air as adults.

Cucumber beetles are difficult to control without endangering coveted beneficial insects such as bees, ladybeetles, parasitic wasps and lacewings. They have few natural enemies except for the tachinid fly — a parasitic fly that lays its eggs in the beetle, eventually destroying it.

There are a few things you can do to reduce the impact these little insects have on your garden.

Knowing its life cycle helps. The cucumber beetle overwinters in the soil around plant roots where it lays its eggs.

Fall clean up and cultivating the soil around shrubs will help rid your garden of the hibernating beetles and its eggs and will disturb root-chewing larvae.

After the eggs hatch in early spring you must go into full attack to reduce the number of beetles and interrupt the life cycle.

▪  Patrol the garden in the early morning. Carry a small container of soapy water and knock cucumber beetles into the bucket. If you do this on a regular basis, you will be surprised with the results.

▪  Heavy mulching, 4 inches or more, may deter cucumber beetles from laying eggs in the ground.

▪  Cultivate the ground around plants in the fall and spring to expose the eggs, but be careful not to damage plant roots.

It is not recommended that you spray insecticides to alleviate the spotted cucumber beetle. Insecticides will often do more harm than good by destroying beneficial insects.

For more information on the cucumber beetle go to IPM Pest Notes at www.ipm.ucdavis.edu/PMG/r116300511.html or call the UCCE Master Gardener helpline if you have additional questions.

Lee Oliphant is a UCCE Master Gardener.

Got a gardening question?

In San Luis Obispo call 781-5939, Arroyo Grande, 473-7190 and Templeton, 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 781-5939.