Ornamental cherry trees throughout the 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 through Pierce and Thurston counties and east since.
“It’s disconcerting because it can lead to the death of trees, and it’s moving into other fruit trees as well,” said Eric LaGasa, chief entomologist with the state Department of Agriculture.
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 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.
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 tunnel between the bark and the 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
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