PORTLAND, Ore. (KOIN) – An invasive insect has caused noticeable damage to Oregon’s white oak trees in 2022, the Oregon Department of Forestry said.
The oak lace bug, scientific name Corythucha arcuata, has been in Oregon since 2015, but the damage it’s causing is on the rise, according to officials.
The insect is native from southern Canada to the eastern, central and southern United States. In Oregon, it’s mostly a problem for urban oaks, but it can also infest native trees.
Adult oak lace bugs are about an eighth of an inch long and transparent. They look similar to non-native azalea lace bugs that have been attacking azaleas and rhododendrons in Oregon in recent years.
The Oregon Department of Forestry said lace bugs occur on the underside of leaves. They suck plant juices from plant cells that contain chlorophyll and cause the leaves to turn yellow.
Anyone who thinks they’ve spotted a leaf that’s being attacked by lace bugs should look at its underside to confirm. They might see adult lace bugs, cast skins of nymphs and black droplets of excrement.
Forestry officials do not recommend treating plants for the insect because they are typically only an aesthetic pest that does not persist year after year. White oaks that are damaged will drop their leaves in the fall and reflush the next year as normal.
“It’s fairly common in fall to see yellowing and browning leaves on Oregon white oak. The color change can also be due to normal attacks from other insects, such as gall-making flies and wasps, leaf-mining caterpillars and flies, which come to an end when cold weather arrives,” the Oregon Department of Forestry said in a press release.
Brown leaves can also be damaged from squirrels digging at twig gall grubs, the department of forestry said.
Experts said oaks and other Oregon trees have been stressed this year by ongoing droughts and hot weather. This can be another reason for their leaves to turn brown earlier than normal.
Fertilizing trees will not “green up” the damaged leaves, the Oregon Department of Forestry said. Sometimes fertilizing a tree not only provides more nutrients to the tree, but also to the insects that attack it.
The Oregon Department of Forestry said oak lace bugs can bite, although their bites usually only cause a mild sting. They do not seek out humans, but can fall from trees onto humans and may bite them.