Arnold Hara next to his tree disinfection chambers

Arnold Hara of the University of Hawaiʻi at Mānoa College of Tropical Agricultures and Human Resources’ Department of Plant and Environmental Protection Sciences discovered that Christmas trees remain fresh and green when given hot tap water to absorb. Tree stems can absorb hot water more readily than cold. This discovery came about from the department’s goal of protecting the islands from a banana slug infestation through tree disinfestation.

Drenching floods in the Pacific Northwest, where the majority of Christmas trees imported to Hawaiʻi are grown, are the reason Hara’s plant disinfestation spray chambers were needed for this year’s shipments. The ground became so soaked that banana slugs slithered into the trees to escape from drowning, and when the trees were cut down and shipped over, the slug came over as well.

This isn’t the first year they’ve been discovered in tree shipments, but banana slugs are far more numerous than ever before, infesting at least half the containers. The bright yellow slugs may be carrying rat lungworm disease and are not welcome to the islands. Banana slugs aren’t found here yet and the Hawaiʻi Department of Agriculture’s Plant Quarantine division and Hara intend to keep it that way.

Hara’s disinfestation chamber, which is usually employed to keep coqui frogs from leaving the Big Island, is constructed from ordinary shipping containers lined with pipes and spray nozzles. The chambers are deceptively simple and extremely effective. Fifty to seventy trees are piled inside and bathed in 118-degree water for eight minutes and the water is even recirculated and reused.

Slugs aren’t the only pests sheltering in the branches of the Christmas trees—a Western fence lizard, a salamander, wasps and frogs have also been found in this year’s shipments. The state has no other feasible method of disinfesting the trees besides manually shaking each one, making Hara’s invention not only ingenious but critical to the biosecurity of the islands.