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Washington State University
WSU Puyallup Ornamental Plant Pathology

Christmas Tree Research Program


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.

Grower Resources

PNW Handbook Resources

WSU Extension Documents

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

Recent Research Projects

Douglas-fir Twig Weevil

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.

Do you suspect twig weevil on your trees?

Click here (PDF) for more information on symptoms and how you can request we sample for this pest.


Contact Us

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.

<i>Megastigmus</i> larvae emerging from 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 that have superior needle retention by testing detached branches.

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.