KETCHIKAN - Spruce aphids have been on the rise throughout much of Southeast Alaska, and now the U.S. Forest Service is trying different methods for controlling the pests.
Alaska Region entomologist Mark Schultz said Tuesday that the Forest Service is testing three different treatment methods on aphid-ridden Sitka spruce trees around Craig, Sitka and Juneau. The methods include a soil treatment, a liquid injection method and "ace caps," which are powder-containing capsules that are driven into the trunks of trees.
Schultz said all three treatments appear to be effective. None will kill all aphids on a tree but they can reduce the aphid population enough to keep the tree alive, he said.
While there are records of spruce aphids in Southeast as far back as the 1930s, the pest didn't become a concern until the 1990s when numbers rose, Schultz said.
"It's been going on continuously since then," he said, with the same trees getting attacked year after year.
Schultz said it appears that certain Sitka spruce trees have fewer natural defenses, and therefore are easier targets for the spruce aphid. Those trees also could have a higher nutritional content for the bugs, which suck sap directly from the needles.
While spruce aphids are not a forest-wide problem, they are a concern because the trees that are attacked most often are along the coast, where eagles nest and where people visiting the forest easily can see the damage.
While insects that prey on aphids, such as ladybugs, can help, he said, aphids remain a problem for some trees. A tree that has spruce aphids generally will start to get brown from the bottom up, and the needles will thin over several years.
People who want to treat their own trees can purchase ace caps, which are safer for humans to handle than other treatments, according to the Forest Service. The capsules contain the aphid-killing compound in plastic sleeves that aren't punctured until the sleeves are pounded into a hole in the trunk. The compound is then released, and travels through the tree's system to the needles.