Aspen trees in Fishlake National Forest, Utah, August 5, 2021 | File photo by Ammon Teare, St. George News
NS. GEORGE – Oyster shell scales, an invasive insect that can weaken and kill aspen trees, was recently confirmed in native forests in Utah, and experts advise caution when removing trees for firewood.
Oyster shell scales cover the bark of an aspen in Arizona, date not given | Photo courtesy Utah State Extension, St. George News
According to a press release from the Utah State University Extension, the insect has been in the United States since the 18th century. However, the USDA Forest Service’s Forest Health Protection program only recently opened its presence in the Uinta-Wasatch-Cache National Forest in Pole Canyon east of the Provo- Area confirmed.
“The quaking aspen is the most widespread tree species in North America and adds an important component of biodiversity, wildlife habitat and fall color to the Utah landscapes,” said Darren McAvoy, assistant professor of forestry at USU Extension, in the press release. “This pest poses a significant threat to the health of our Utah forests, and management options are limited and require further research.”
According to McAvoy, young trees are particularly susceptible to oyster shell scales, which is a particular challenge because young trees are important for replacement and many forests in Utah are already lacking younger aspen trees.
“In the past, other invasive species in the United States have practically wiped out certain tree species, including the American chestnut and western white pine,” he said. “The oyster shell scale is known to have killed large groups of native forest tree species in several eastern states. It is currently causing significant damage to aspen trees in northern Arizona, where it has been active for the past decade, weakening and killing aspen trees below 2,200 feet. “
McAvoy said that oyster shell scales are a tiny sap-sucking insect that ripens over the course of the summer to develop a waxy outer shell that looks like a tiny oyster or clam shell attached to the bark of the tree. Insects tend to cluster on the shady side of trees and branches and avoid direct sunlight. Initially, they attack a small part of a tree, but can eventually encrust entire branches and cause the branches to die, which leads to the tree’s death.
The crown of an aspen in Arizona dies after being attacked by oyster shell scales, date not given | Photo by Justin Williams via U.S. Forest Service, St. George News
“Because of this, it is important to be extremely careful not to bring any firewood infected with the insects into a forest,” he said.
Although there are more than 100 known oyster shell host species, it is best known for its effects on ash, aspen, willow, poplar, and boxelder in Utah. Although strategies for management are limited, the first step is to monitor its spread.
“Applying fire to the affected landscape seems like the most promising management strategy for controlling oyster shell spread, but we are just beginning to learn about it, so more research is needed to understand this relationship,” said McAvoy.
Managers can help with surveillance by sending confirmed sightings of oyster shell scales, including a GPS location, photo, and an affected host species, to Justin Williams, USDA Forest Service, Forest Health Protection Ogden Field Office.
Click here to preview the magazine article on Oyster Shell Scale by Conner Crouch of the Northern Arizona University School of Forestry.
Written by JULENE REESE, USU Extension.
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