Oregon’s frantic Christmas tree harvest is winding down. In just a couple of weeks, seven and half million trees are cut and shipped to retail yards around the world. Only 8 percent of those harvested remain in Oregon. This is a busy time for Oregon Department of Agriculture (ODA) inspectors and their counterparts in receiving states and countries. All of them are doing their best to ensure that pests and diseases are not hitchhiking on the trees.
Before coming to Oregon, I was an inspector in Bermuda, and I often looked at Christmas trees on the docks in the sunny, warm Hamilton harbor. Truck drivers there traditionally take a small branch from the first Christmas tree shipment and insert it in their truck’s grill. Bermudians smile when they see that little reminder of the approaching holidays (Christmas & Boxing Day).
Every one knows Christmas trees vary a lot in shape and desirability from a consumer’s point of view. None of that matters to inspectors. They focus on insects, slugs, tree frogs, Swiss needle cast, and other potential hitchhiking invasive species. From my days in Bermuda, I remember trees from Canada being the cleanest and trees from the Southeast United States being the buggiest. Whether or not there had been a hard frost prior to harvest made a big difference. Oregon trees were always lush and green, but if they hadn’t been exposed to a frost, they were carrying hitchhikers. We’d thump the trunks on the pavement and look for potential pests among the critters that dropped out.
Bermuda, like many islands, has been severely impacted by harmful invaders, including a scale insect that nearly wiped out the endemic Bermuda cedar. They have good reason to be careful with imported plant material.
So far, 2011 has been a good year for Oregon Christmas tree exports. A total of 99 percent of the trees that were certified for export also passed their import inspection at the other end. The few that didn’t included five truckloads rejected at the Mexican border (yellowjackets, weevils), one container turned back in Japan (strawberry root weevil), three fumigated in Guam (spiders), six held in Hawaii (slugs), and one held in Columbia (unidentified bug). Yellowjackets, slugs, and weevils are all known invaders; hats off to the sharp-eyed inspectors that found them.
Inspections are important in the fight against invasive species, but they are not a panacea. As with other commodities, only a small percentage of Christmas trees are checked on either end. The reason is simple; there are a lot of trees and only a few inspectors. Oregon has 10 inspectors working full time on Christmas trees in the fall. That seems like a lot, but if we estimate that 6,900,000 trees are exported (92 percent of total harvest) and the entire harvest happens over 20 working days, each inspector would have to look at 1.2 trees per second to inspect every tree! The best they can do is look at a sample and catch the obvious problems.
What the world really needs is a way to “pasteurize” Christmas trees. Traditionally, trees were shipped straight from the field “as is”. Many growers now use mechanical shakers to remove dead needles and surface hitchhikers. That helps, and some markets now require shaking. Unfortunately, no one has developed a standard, thus the efficacy varies depending on the speed and duration of the shaking. Starting this year, Mexico required 15 seconds of shaking at 700 rpm as well as an insecticide spray prior to harvest. That seems like overkill. Spinning, bouncing, and blowing have also been tried, but no one has tested the efficacy of these methods.
This year ODA started testing different shaking and spray regimes. It is a first step toward developing standard best management practices that will reliably remove potential pests from these famous holiday icons.
In my dreams, we would offer substantial monetary prize for the first person to develop a fast and economical way to “pasteurize” Christmas trees. We could name the process after the developer, ______(your name here)-ize, so Louis Pasteur could quit turning in his grave, and we could eliminate Christmas trees as a pathway for introduction of invasive species. Wouldn’t that be nice?
None of this matters to Oregonians if they cut or choose locally grown trees. We’re lucky to live where Christmas trees are beautiful, inexpensive, and abundant. For us, the best practice is to thump the trunk in the driveway a couple of times before bringing the tree inside. Your kids might enjoy looking for native bugs among the dead needles, and you won’t bring these annoying Christmas guests inside!