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Ornamental cherry trees throughout South Sound are in decline because of a tiny moth whose larva tunnels and feeds beneath the bark of the tree.
It’s called cherry bark tortrix, an invader from British Columbia that appeared in Whatcom County about 20 years ago and has been pushing steadily south and east since.
“Here in the Olympia … we’re definitely seeing increased populations and pressure on trees,” noted Eric LaGasa, chief entomologist with the state Department of Agriculture. “It’s disconcerting because it can lead to the death of trees, and it’s moving into other fruit trees as well.”
LaGasa said one of the most glaring examples of an infestation in a public setting is the Bicentennial Grove of 13 Yoshino Japanese flowering cherry trees planted in 1976 on the Capitol Campus near 11th Avenue and Capitol Way. Several of the trees have dead and dying main branches.
The Department of Enterprise Services has yet to determine a course of action for the flowering cherry trees, department spokesman Jim Erskine said.
Lawn and landscape companies are seeing increased numbers of infested trees among their customers, who often don’t detect the subtle signs of an infestation until tree limbs and trees start to die.
“We’re currently treating hundreds of trees and getting lots of calls on rapidly declining trees,” said Evan Ogden, a senior plant health technician for Wolbert’s, a South Sound landscape-maintenance company.
Late September and early October is the best time to use a prescribed pesticide to control an infestation, Ogden said. That’s when the larva is doing some housecleaning, pushing small deposits of reddish-orange larval waste out their tunnels to the bark’s exterior, usually in the cracks and crevices of the trunk and main branches.
Ogden sprayed the trunk of a stately ornamental cherry tree at the west Olympia home of Paul Felver after showing the homeowner the hard-to-see sign of the larvae on the trunk of the tree.
“I don’t want to lose that tree,” Felver said.
“The larva is mining its way around in the bark, but we’re catching it in time,” Ogden said.
Organic options for controlling the pest include relying on parasitic wasps to prey on the larvae or covering areas of cracked and damaged bark with a Kaolin clay spray to keep the insects from penetrating the tree bark, according to Sound Solutions, a Seattle-based organic pest-management company.
The larvae feed on the bark and outer sapwood and tunnels between the bark and tree’s cambium layer, interfering with the tree’s ability to transport nutrients to the roots. A cherry bark tortrix infestation can also weaken the tree, making it vulnerable to bark beetles, fungi and frost damage.
The Washington State University Extension Service encourages tree owners to consult the most recent Pacific Northwest Insect Management Handbook, contact the local cooperative extension office or go to pep.wsu.edu/hortsense.
John Dodge: 360-754-5444 jdodge@theolympian.com
