State agriculture inspectors found slugs in six of 60 shipping containers of Christmas trees arriving over the past weekend in Hawaii and held them.
Last year, 50 percent of containers were infested with slugs and other pests.
The Oregon Department of Agriculture increased its monitoring this year over the harvesting, handling and shipping of Christmas trees to Hawaii, the Hawaii Department of Agriculture said in a news release.
Oregon agriculture inspectors are in Hawaii to watch the inspections.
In October, two Hawaii agriculture inspectors traveled to Oregon to observe harvesting and packing of some of the trees that arrived this weekend.
The state will use hot water to treat the trees contained in shipping containers being held for pests.