PPO > Christmas Trees

Christmas Tree Research Program

Introduction

The Pacific Northwest produces close to one third of the Christmas trees sold each year nationally.

The goal of our research program is to provide growers and retailers with research-based information that creates a high-quality Christmas tree products for consumers.

We strive to accomplish this goal by conducting applied research focused on reducing the impacts of pests and pathogens and increasing the longevity of trees after they are harvested.

the base of a tree with small cankers showing on the stem
conifer twigs showing rusty red blotches

2022 mortality at Christmas tree farm caused by drought and Armillaria root rot

Grower Resources

PNW Handbook Resources

WSU Extension Documents

Click on the links below to visit the WSU Extension publication website. These resources are available to download for free.

Developing Quality Christmas Trees in the Pacific Northwest

link to "Developing quality christmas trees in the pacific northwest" above

Growing Christmas Trees in the Pacific Northwest (pdf)

link to "Growing christmas trees in the Pacific Northwest" above

Identifying and Managing Christmas Tree Problems

link to "Identifying and Managing Christmas Tree Problems" above

Weed and Vegetation Management in Christmas Trees

link to "weed and vegetation management in Christmas trees" above

Recent Research Projects

Douglas-fir Twig Weevil

a small christmas tree with arrows pointing to the discoloration cause by insect damage
Christmas tree damaged by twig weevil

The Douglas-fir twig weevil recently emerged as a important pest of true firs in the Pacific Northwest. Outbreaks of this pest have impacted the tree export market by causing load rejections in markets with neighbor countries such as Mexico. The damage from these twig weevils also affect the quality of trees for the domestic market.

Our program, in collaboration with Oregon State University Extension, aims to:

  1. Reveal the diversity of twig weevils associated with different Christmas tree species.
  2. Increase our understanding of their life cycles to identify critical stages for control.
  3. Develop a guide for growers to identify and control twig weevil populations.

Feel free to contact us for more information.

Heat Treatments for Imported Seed

Turkish and Nordmann fir seedlings are often grown from imported seed because of limited domestic sources. However, the importation of these seeds is often restricted and limited because of contamination by Megastigmus larvae.  For example, a substantial amount of seed is destroyed each year following the detection of these larvae because there are no currently approved treatments.

Therefore, a priority research topic for our program is to evaluate the potential of heat treatments to eradicate Megastigmus larvae in infested Turkish and Nordmann fir seeds. This research is made possible through support from the Christmas Tree Promotion Board and USDA APHIS.

a small shiny yellow-white ribbed worm with a faint black spot inside a cut-open conifer seed
Larva emerging from Noble Fir tree seed

Ongoing Research

Much of our pest and disease research has focused on the following topics:

  • the development and management of Annosus root rot,
  • the development of effective methods to reduce insect populations that restrict export markets,
  • and the identification of sources of trees with resistance to common diseases and insect pests such as:
    • Phytophthora root rot,
    • current season needle necrosis,
    • Grovesiellia canker,
    • spider mites,
    • and twig aphids.

Our postharvest research has focused on the identification of sources of true firs with superior needle retention by testing detached branches.

needles of two branches showing some discoloration and yellowing
two attached twigs, the left a rusty brown and the right greener, both with apparently healthy tips
a branch with needles curling and turning brown at the margins
green needles with rough yellow balls growing off the stem
closeup on needles with small black dots indicating disease
needles whose discoloration starts suddenly part of the way up each needle
needles growing thickly off a branch. approximately half the needles are brown
closeup on needles. some are sickly light green with darker brown spots and blotches
bright green needles turning yellow to red and brown in uneven patterns
small branches with obvious bulgy growths on the bases and ends
closeup on the space between branches on the stem of a conifer. the needles coming off the stem are bright red-brown and show evidence of tiny webs
closeup of a deformed branch with yellowing needles sticking out of corky red growths

Christmas tree foliar symptoms

Publications and Reports

  1. A Survey of Phytophthora spp. Associated with Abies in U.S. Christmas Tree Farms. K. M. McKeever and G. A. Chastagner, Plant Disease 2016 100:6, 1161-1169
  2. Postharvest Quality of Noble and Nordmann Fir Christmas Trees. G. A. Chastagner and K. L. Riley, American Society for Horticultural Science, 2003: 38:3.
  3. The Christmas Tree: Traditions, Production, and Diseases. G. A. Chastagner and M. D. Benson, Plant Health Progress 2000 1:1
  4. Christmas Tree Diseases, Insects, and Disorders In The Pacific Northwest: Identification and Management.1997. WSU Extension Publication MISC0186.

Christmas tree foliar symptoms and stem canker

green needles that turn suddenly red and white
three apparently healthy twigs branch off from a spot with many reddish brown needles
closeup on needles. some have turned light brown and gone wavy
small tree with thick green needles. white shows through the needles and the light shows that some of the twigs are entirely wrapped in something white
closeup on a twig with tiny cankers growing out of the bark. one red needle can be seen at the top.

WSU Puyallup Research & Extension Center
2606 West Pioneer, Puyallup, WA, 98371-4998 USA
Last updated 9/24/2025