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In a strawberry patch next to an apple orchard, technicians David Roys (left) and Cathy Peters and entomologist Tom Unruh inspect plants for strawberry leafrollers.

In a strawberry patch next to an apple orchard, technicians David Roys (left) and Cathy Peters and entomologist Tom Unruh inspect plants for strawberry leafrollers.

A rose garden to help the leafroller parasite Colpoclypeus florus survive the winter should be close to the orchard, but not so close that pesticides will drift on it. It should be in a place that is easy to irrigate.

Dr. Tom Unruh, entomologist with the U.S. Department of Agriculture in Yakima, Washington, recommends planting a strip or two of roses about 30 to 60 feet long. Wild roses, such as Rosa woodsii or Rosa nutkana (the Nootka rose) are available from nurseries that specialize in habitat restoration. Alternatively, they can be dug from wild patches in approved locations. It is best to dig them in the early spring, before bud break.

To prepare the bed, lay down a black weed cloth to cover emerging weeds. Cut openings to plant the roses two to three feet apart. Bring water to the site, using black tubing spliced into the irrigation lines. Keep the soil around the plants damp, especially during the first year. Within a couple of years, with plenty of water and fertilizer, the roses will grow aggressively and keep the weeds down.

Roses and strawberries

Unruh said the rose bed can be a more effective overwintering site for the parasite if it includes strawberry plants, which are a preferred host of the strawberry leafroller. Studies have shown that although Colpoclypeus is twice as likely to parasitize a strawberry leafroller when it’s on a rose plant, there are ten to twenty times more strawberry leafrollers on strawberry plants.

A mixed planting of roses and strawberries can be difficult to manage, as the roses will eventually shade out the strawberries and kill them. The ideal is to establish separate gardens of roses and strawberries with a dry patch between so that they don’t grow into each other, Unruh said.

Strawberry leafrollers will need to be released into the roses and strawberries. They can be found in wild roses on hillsides and along ditch banks in the upper Yakima Valley, and along roadsides near Ellensburg.

There is also a large patch on the hillside below WSU’s Columbia View research orchard north of Wenatchee. In early to mid-June, the leaves of infested roses will be folded in half, taco-like, with the yellow larva inside. Infested terminals can be cut from the bushes and tucked into the plants you want to infest.

For more information on planting wild roses and strawberries to enhance biological control of leafrollers, check the Web site at www.ars.usda.gov/Research/docs. htm?docid=14646.