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Garden patrol: Beetles

This is the time of year that those pesky cucumber beetles show up, and if you are keeping an eye on your vegetable garden, you may find them at your place, too.

Whether striped or spotted, these bugs are only about 1/4 inch long and have a black head. The striped ones are greenish-yellow, with three black stripes. The spotted ones may be mistaken for ladybugs, as the main difference in appearance is that the spotted cucumber beetles are greenish-yellow, not red.

Cucumber beetles do not confine their diet to cucumbers. The larvae will attack roots and stems of all members of the cucurbit family, including melons, pumpkins, gourds and squash, while the adults feast on the blossoms and pollen. And just for good measure, you might find them on asparagus, eggplant, potatoes and some fruits; they have been found in 29 plant families. Heavy infestations will attack corn roots to the point that the corn plant falls over, although that is usually a problem of our more southern neighbors.

To add insult to injury, the adults can also carry bacterial mosaic and wilt diseases. Symptoms of these diseases are the wilting and death of plants.

Knowing more about their life habits, as well as how to rid our gardens of them, will help keep the beetle damage to a minimum. The insects overwinter in garden debris, including piles of dead grass, weeds and extra mulch that has been raked to the side of the garden. This is one more reason to keep a clean garden, especially in the late fall. It's also a good practice at the end of the season to disturb the soil where you've had an infestation to help eliminate any bug motels.

In early spring, when temperatures begin to go above 50 degrees, each female will lay 200 to 800 eggs on the underside of leaves. As the larvae emerge, they will begin feeding on and burrowing into the stems of the cucurbits. Keep young plants well watered, as stressed plants are always easier prey.

In planning the garden, some people have had luck with planting "bait plants" such as zucchini or pumpkins around the perimeter of the garden to help attract the beetles to them, and thus away from the rest of the garden. The beetles don't like nasturtiums, old-fashioned marigolds, radishes, calendula or broccoli, so incorporating those with your cucumber patch may help. Natural predators include bats (the animal, not the ones used in baseball), lacewings, ladybugs (they eat the eggs), praying mantis and parasitic nematodes.

As for what to do if you have cucumber beetles now, the most discouraging thing is that the hard-coated beetle is not easily controlled with insecticides. Using a shop or hand vac or hand-picking them and dropping them into a container of soapy water are more effective. Yellow cups or yellow pieces of cardboard painted with Tanglefoot will help, as well. Try spraying the underside of leaves with Safer insecticidal soap or with soapy water to help eliminate the egg clusters. You will need to patrol your garden daily, as they will not be eliminated with one visit.

Coming up: Winter veggie gardens will be the topic of a class taught by Master Gardener Janet Rodkey from 7 to 9 p.m. on Thursday, July 26. The class will be held at the Southern Oregon Research and Extension Center, 569 Hanley Road, Central Point. The class costs $5. Call 541-776-7371 for details.

Carol Oneal is a past president of the OSU Jackson County Master Gardeners Association. Email her at diggit1225@gmail.com.