Noble fir, the iconic tree of holiday greenery, is under attack by a disease known as purple needle eater. The mysterious disease attacks new growth, causing needles to turn purple and die.
“A bough harvesting contractor wants to be able to go into a stand of trees and cut boughs like crazy without worrying about disease,” said Christmas tree expert Gary Chastagner. “In some cases, the needle cast problem is so bad there’s virtually no usable boughs at all.”
Wet spring encourages disease
Chastagner, a plant pathologist at the Washington State University Puyallup Research and Extension Center, said that in some areas needle cast disease has caused significant reductions in the production and quality of noble fir boughs as well as some Christmas trees in the Pacific Northwest.
In the past few years, purple needle eater has severely impacted a major source of noble fir boughs at high elevations near Mount St. Helens in Washington, but in 2014 a similar looking disease was detected at low-elevation sites.
Chastagner said that 2014 was a particularly bad year for some sites – where 95 to 100 percent of noble fir boughs had the disease – because the conditions – prolonged, wet spring weather during new growth – were optimal for the disease. It will take two to three years before the damaged boughs have enough growth to harvest.
Diseases new to Pacific Northwest
Initial testing of stands at both elevations revealed a complex of pathogens that includes two that have never been detected before on noble fir in the Pacific Northwest.
The particular pathogen that’s behind the purple needle eater name, Delphinella abietis, has been reported on other conifers and has been found on noble fir in Europe but not in the Pacific Northwest.
“The only place we’ve seen purple needle eater before is in high-elevation stands,” Chastagner said. “Seeing it impact low-elevation Christmas trees is new.”
Some new fungicides to control this disease are available in Europe but not in the United States.
The other new pathogen that has been found on some high-elevation trees, Phacidiopycnis, is the same as one that’s commonly found among apples held in storage after harvest. This fungus was only previously found on conifers in China and on Pacific madrone in the Pacific Northwest.
Help for growers, harvesters
It’s unclear why the disease is showing up now at low-elevation sites and why growers haven’t been able to control it. Normally, applying fungicide in spring just after growth emerges from new buds is an effective treatment.
Chastagner is conducting research to get a better understanding of the diseases, their prevalence and location as well as which fungicides are most effective. The research is designed to help growers and harvesters manage the problem. It is funded by a grant from the Washington State Department of Agriculture Specialty Crop Block Grant Program.
Given the increasing reliance on noble fir grown at low elevations, Chastagner and his research team will also study how well boughs from these locations hold up after harvest. The industry favors boughs from higher elevations for the dark bluish green color and needle retention.
Increasing demand, diminishing supply
Most noble fir boughs in Washington have been harvested from trees planted at high-elevation sites around Mount St. Helens 35 years ago after the volcano erupted. As these trees become too mature to harvest, the industry is looking to former Christmas tree plantations at low elevations as a source of the holiday greenery.
For Christmas tree plantations, growing boughs also serves as a buffer against the boom and bust cycle of Christmas tree production.
“Growers can ship it to processors or make products themselves,” Chastagner said. “They’re sort of vertically integrated.”
The Pacific Northwest leads the nation in the production of Christmas trees and boughs, a multimillion-dollar industry. Noble fir represents nearly half of the production of the region’s Christmas trees. Demand for noble fir has increased in recent years, in part because the region is known for high quality boughs and Christmas trees.
Gary Chastagner, WSU Department of Plant Pathology, 253-445-4528, firstname.lastname@example.org
Source: Washington State University Puyallup Research and Extension Center