Boxwood blight, cause by the fungi Calonectria henricotiae and C. pseudonaviculata (syn. Cylindrocladium buxicola), is not native to the US. The pathogen was most likely transported to the US on boxwood from nurseries in Europe.
- First known find in Pacific Northwest: At a nursery in Washington County, Oregon in December 2011.
- Found in the eastern US: At nurseries in Surry County, North Carolina and Carroll County, Virginia, and at a residential landscape in Middlesex County, Connecticut in October 2011.
All boxwood species may be susceptible to blight, however American boxwood varieties appear to be particularly vulnerable. The boxwood family Buxaceae and a member of this family, Sarcococca, have been shown to be susceptible to the fungus C. buxicola.
Symptoms
- Light or dark brown circular leaf spotting
- Black longitudinal or diamond shaped lesions on stems
- Results in defoliation of leaves and an overall straw colored appearance of the plant
Disease transmission is increased in moist environments, making host plants in greenhouses particularly susceptible. The fungus can form resting structures (chlamydospores and microsclerotia) that can survive for years on host organic debris in the soil. Mortality most often occurs in seedlings, but may also take place in older plants, especially if infected with a secondary pathogen.
Geographic distribution
Boxwood blight has been reported throughout Europe, the United Kingdom, and New Zealand. In the US, 16 states have reported boxwood blight: Alabama, Connecticut, Delaware, Georgia, Kentucky, Maryland, Massachusetts, New Jersey, New York, North Carolina, Ohio, Oregon, Pennsylvania, Rhode Island, Tennessee, and Virginia. In Canada, it has been found in British Columbia, Ontario, and Quebec.
Nursery Cleanliness Program for Boxwood Blight
This voluntary program of inspections and best management procedures is designed to help a nursery provide clean boxwood nursery stock to their customers with more confidence. Please contact your Nursery inspector or nursery@oda.oregon.gov for more information on how to enroll. The compliance agreement and audit checklist below will be used during an on-site audit for program participants.
Approved training options for nurseries in 2023:
Please note that we encourage a "Teach the Teacher" philosophy with mangers and supervisors participating in greater levels of training to learn techniques to successfully scout for and recognize boxwood blight. Supervisors should then use that knowledge to train their staff in these skills. All staff who touch boxwood plants (trimming, propagating, etc.) need to, at minimum, be shown the boxwood blight poster so they can recognize boxwood blight symptoms while in the production areas (your nursery inspector can provide you with a weather-resistant poster).
Training Option 1 (Most in-depth): any training provided by Dr. Luisa Santa Maria, OSU Extension Agent. She can provide virtual courses in English and Spanish as well as visit your nursery to meet with the staff. She covers topics such as scouting, identifying symptoms, sanitation, and customizing best management practices for your nursery.
Training Option 2 (Moderately in-depth for scouting): this video produced by the Boxwood Blight Insight Group (BBIG), and presented by OSU's Dr. Jerry Weiland, is an excellent tool for scouting managers and scouting teams to watch. The video is around 5 mintues long and is available in both English and Spanish.
Training Option 3 (minimum requirement for field staff, insufficient option for supervisors): OSU's Luisa Santamaria has produced a weather-resistant (corrugated plastic) poster showing symptomology of boxwood blight infections with descriptions in English and Spanish. The minimum training requirement is for all staff who handle boxwood to be shown this poster by their supervisor so that they can easily refer to it as a guide. These posters are currently provided for free by the ODA, please contact your nursery inspector to get one or more copies.
Training Option 4: If your nursery already provides in-house training for boxwood blight, your program may qualify for the training requirement in lieu of the first two options. Please contact Kara.Mills@oda.oregon.gov to discuss your training program.
Boxwood Blight Cleanliness Program Participant list 2022-2023
- Bailey Nurseries Inc. (Dayton, Sauvie Island, Yamhill)
- Eshraghi Nurseries LLC (Hillsboro)
- Iseli Nursery (Boring)
- MS Growers – Instahedge (Canby)
- Russell’s Nursery (Aurora)
- TSW Nursery Sales Inc. (Aurora)
- Wandersleben (Lebanon)