Pests in the Garden

By Yvonne Rasmussen, U. C. Master Gardener

The recent nice weather has made everyone more active in the garden, including the insects. Some insects, although large and rather dramatic, are not serious pests in the garden, while other smaller ones can be very problematic, especially if they are new to our area.

The large, white, C-shaped grub with a brown head and gray tail may be big—it measures about one inch long—but it does no harm in the garden. It is the larval stage of a scarab beetle called the masked chafer or, alternatively, the May or June beetle. It generally matures in May or June and is rarely a pest unless it is in your lawn. In lawns, these grubs can cause brown spots where they eat grass roots. In your garden soil, you can ignore them or remove them by hand. Toss them onto a dry surface, where they will dehydrate and die. Often birds will eat them.

On the other hand, the spotted winged drosophila (SWD) is a minute insect that can ruin your fruit crop. First spotted in California three years ago, it is a serious invasive fly. It has since spread to all the fruit-producing areas of California, Oregon and Washington.  It is related to the vinegar fly that likes the overripe fruit on your kitchen counter, but this fly attacks ripening fruit.

The male has two spots on the tip of its wings. The female lays her eggs in whole ripe fruit. This insect is a big concern for anyone growing soft fruits such as cherries, raspberries, blackberries, blueberries, strawberries, plums, nectarines and peaches. It thrives in temperatures from 70°F to 80°F, with high humidity, so coastal crops and early-season fruits are most at risk.

The damage makes it possible for fungi to get into the fruit, which accelerates the rotting process. Only two to three days after the female lays her eggs inside, the fruit will start to collapse and wrinkle. So how can you protect your fruit?

 Here are a few tips for homeowners:

 Set up monitoring traps early in the season, which means now. You can make traps easily from heavy plastic 16-ounce or 32-ounce cups with tight-fitting lids. Drill small holes (1/16 to 3/8 inch) along the top sides. Fill the cup with about two inches of cider vinegar and one drop of dish soap. Place a yellow sticky card (available at many nurseries and hardware stores) loosely arched inside near the top to trap flies. Hang the trap in a tree near the fruit, or place it on the ground in a cool, shady spot. Check traps weekly to collect the flies from the liquid and the sticky card. You will likely catch several kinds of flies; use a magnifying hand lens to identify the SWDs. Even if you don’t identify the flies you catch, you can use these traps to help reduce the fly population around your fruit trees or bushes.

 Use fine netting to keep flies away from fruit before it begins to ripen. You can build a cage around your trees to keep out the flies, but make sure it has no gaps or holes and make sure your netting is very fine.  These flies are really small. The same netting will protect fruit from bird damage, too.

 Pick ripe fruit frequently. Flies attack soft ripe fruit, so harvest several times a week to make sure you get to eat it before they do.

 Clean up and destroy all fallen fruit and do not leave any overripe fruit on the tree or plant.

 A few pesticides are available for home use. Follow the label directions carefully and do not spray when bees are active.

 Napa County Master Gardeners will be hosting two workshops this summer on insects in the garden. On Saturday, June 18, “Debugging Garden Bugs” will offer tips for insect identification. On Thursday, June 23, “Get to Know Your Garden Bugs” will present a more general program designed for families.

For more information on controlling the spotted winged drosophila, visit our website (see below). Look under Napa County Programs for Master Gardeners, then under Seasonal Topics for the information on SWD, or come by our office for complete information.

Master Gardeners are volunteers who help the University of California reach the gardening public with home gardening information. Napa County Master Gardeners (http://cenapa.ucdavis.edu) are available to answer gardening questions in person or by phone, Monday, Wednesday and Friday, 9 a.m. to Noon, at the U. C. Cooperative Extension office, 1710 Soscol Avenue, Suite 4, Napa, 707-253-4221, or from outside City of Napa toll-free at 877-279-3065. Or e-mail your garden questions by following the guidelines on our web site. Click on Napa, then on Have Garden Questions?

U.C. Master Gardener TV is broadcast weekly on Napa Public Access Cable Television Channel 28, and ATT U-Verse Chanel 99, at 11 a.m. on Thursdays and 7 p.m. on Saturdays. You can also watch it online at www.napavalleytv.org. .

Garden Tour: Save Sunday, May 15, for “Down the Garden Path,” the Napa County Master Gardeners’ garden tour. The tour will showcase seven unique Up Valley gardens owned and maintained by local Master Gardeners. For tickets and more information, visit http://cenapa.ucdavis.edu.

Mobile Help Desk: Bring your gardening questions to the Napa County Master Gardeners mobile help desk on Saturday, April 23, at Mid-City Nursery in American Canyon; and Saturday, April 30, and Sunday, May 1,  at DJ’s Growing Place in Napa. Master Gardeners will be available to answer questions at these locations from 10 a.m. to 2 p.m.

Open Garden Days: Napa County Master Gardeners welcome the public to their demonstration garden at Connolly Ranch on the first Thursday of every month, from April through October, from 10:30 a.m. to noon. Master Gardeners will be on hand to answer questions. Connolly Ranch is at 3141 Browns Valley Road in Napa.

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