Surrounded by sagebrush? Leave it there. Spot buckwheat nearby? Let it be. Come across some stinging nettles? Don’t touch it, but don’t remove it either.
“If you have a patch of stinging nettles around, don’t just chop it down if you don’t need to,” said David James, Washington State University entomologist in March at the WSU Fruit School, a two-day conference in Wenatchee, Washington.
With his presentation to a room full of dozens of tree fruit growers, James shared his list of favorite native plants that attract beneficial insects to vineyards.
That’s right, James specializes in wine grapes but believes many of his portfolio of plants would also work in orchards to attract parasitic wasps, lady beetles, green lacewings and other insects that keep pests at bay.
Granted, vineyards require less irrigation and don’t have as many critical pests as tree fruit, but James says the lessons still work.
The principles are the same, and they’re pretty simple. Most beneficial insects, those that prey on pests or help pollinate, have adapted alongside native plants, so it stands to reason that native plants in and around an orchard or vineyard will attract those insects.
James has data to back it up. Since 2010, he and his research colleagues at WSU’s Irrigated Agricultural Research and Extension Center in Prosser, Washington, have studied how many beneficial insects are attracted to trial plots and commercial vineyards populated with native plants.
The answer: more than those without native plants.
For example, in 2013, his team counted nearly twice the mean number of beneficial insects in four “habitat-enhanced vineyards” — those with native plants in rows and elsewhere — than in four conventional vineyards.
Pests, on the other hand, were about a third of their mean population per leaf between the enhanced and conventional vineyards.
“So, it seemed to work,” he said.
For growers looking to try this for the first time, he suggested yarrow. In damp climates, the erect flowering plant can take over and become a weed, but in the deserts of Washington tree fruit and wine grape regions, it stays low and in control.
What’s more, it’s durable as a ground cover when it’s mowed, walked on and driven over. It had a 97 percent survival rate in his trials and attracted nearly three times the mean number of beneficial insects per trap than his control block.
Another one of his favorites is buckwheat, a broad classification of about 10 species of native flowering plants commonly found near hiking trails of arid hills. They grow low, tolerate drought and attract a broad diversity of beneficial insects, such as lady beetles, predatory thrips and parasitic wasps.
One of his biggest surprises is sagebrush. “In terms of sheer numbers of individual beneficial insects, and they’re mostly parasitic wasps, then sagebrush is the king,” he said.
Several growers at the workshop liked the sound of that. Many of them have new orchards carved out of shrub-steppe habit, where sagebrush dominates. They simply have let it grow close to the exterior blocks.
Mauro Sito, a manager at the Foreman Fruit Co., said he planned to ask around for more information about planting native plant seeds in organic orchards.
“I just recently graduated from WVC (Wenatchee Valley College), and a lot of that stuff is being taught and touched upon, yet at least where I’m at, I don’t really see it implemented much,” Sito said. “And I personally think it would help, especially in organic areas.”
Luke Davies, a 30-year-old, third-generation grower in Orondo, Washington, would like to try native plants and plans to pitch the idea to his father, Paul. “I’ve got to make a pretty strong case in order to sell it,” he said.
The family has just started transitioning some of its 90 acres of tree fruit to organic to capitalize on growing demand and the premium prices. Pest management concerns are the main reason they waited so long.
James’ list went on. Pepperweed is best for attracting lacewing, northern buckwheat for lady beetle, gray rabbitbush for a variety of parasitic wasps.
Nearly all the plants he discussed are available as seed from native plant vendors.
However, he urged growers to ask for native species as opposed to nonnative ornamental versions that won’t have the same insect effect.
He also suggested irrigating them only to get them started, but then leaving them alone; they are adapted to desert climates and don’t need much water.
Overall, he has made use of about $100,000 in research funds from numerous organizations, including the Washington Winegrowers. His work is ongoing because he still has unanswered questions.
He does not know if any of the native plants harbor diseases and hasn’t determined in all cases which plants are easy to establish from seeds.
He also hopes to add a fruit quality analysis to his research to determine if the presence of native plants does any good or ill to the crops.
He has studied 120 different native species. So far, he has narrowed down his research trial plots to 15 different plants and plans to try about six of those on a larger scale, perhaps an acre or two each.
He envisions eventually coming up with recommended mixtures of native seeds and perhaps a field guide to native plants and their use in fruit crops. •
David’s Delightful Dozen
Washington State University entomologist David James provided this list of 12 plants native to Central and Eastern Washington’s tree fruit and viticulture regions that would attract and harbor beneficial insects. “If you have those plants around, then you can be assured that you’re doing some good for beneficial insects,” he said.
—Yarrow (Easy to start from seed and may tolerate the heavier irrigation of tree fruit compared to vineyards.)
—Rabbitbrush (Rivaled sagebrush in sheer number of beneficial insects but attracted a wider diversity.)
—Buckwheats (About 10 different species of them. Plant a variety and get flowers through multiple seasons.)
—Coyote Mint (Attracts the big-eyed bug geocoris, a mite predator.)
– by Ross Courtney