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Nursery Cleanliness Program for Boxwood Blight


A new fungal disease of boxwood was identified in the United States this past year. Cylindrocladium buxicola (syn. C. pseudonaviculatum), commonly known as boxwood blight, was identified on boxwood at a nursery in Washington County, Oregon in December 2011. This is the first known find in the Pacific Northwest. A couple months earlier, the pathogen was found in the eastern United States (October 2011) at nurseries in Surry County, North Carolina and Carroll County, Virginia; and at a residential landscape in Middlesex County, Connecticut. The pathogen was most likely transported on boxwood from nurseries in Europe, where it is known to occur. Boxwood is not native to the United States. 
C. buxicola is a fungus of the boxwood family, Buxaceae. Although all boxwood species may be susceptible to blight, American boxwood varieties appear to be particularly vulnerable. Sarcococca, another member of Buxaceae, has also been shown to be susceptible to the fungus. 
Symptoms on boxwood include light or dark brown circular leaf spotting and black longitudinal or diamond shaped lesions on stems. Progression of the disease 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.

The Program
In cooperation with the National Plant Board, the nursery industry, and many other state departments of agriculture, ODA has initiated the Nursery Cleanliness Program for Boxwood Blight. This is a voluntary program of inspections and best management procedures designed to help a nursery provide clean boxwood nursery stock to their customers with more confidence. To meet the requirements of the Nursery Cleanliness Program for Boxwood Blight, the nursery shall meet the following eight steps.

The Steps
1. Register compliance agreement with the ODA.
2. Adopt the following practices for host plant buy-ins.
  • Purchase buy-ins from nurseries that have been officially inspected and found to be apparently free of boxwood blight or from nurseries that are participants in an official boxwood blight cleanliness program.
  • Inspect buy-ins at the time of delivery.  If symptoms are observed, call the ODA.
  • Isolate buy-ins from other Buxaceae plants on site for a minimum of 30-days.  Buy-ins must be located a minimum of 3 meters (10 feet) from all other Buxaceae plants (including landscape).  Alternatively, a physical barrier or other isolation method approved by the ODA may be used.Position the isolation area so as to prevent water run-off into potting media and host production areas. The isolation area should have a surface that can be easily cleaned of plant debris.  Plant debris shall be removed on a weekly basis. Buy-ins must not be treated with fungicides during the isolation period. Inspect buy-ins for suspicious symptoms weekly and note inspection results on an inspection form.  The inspection form may follow the standard format for the nursery.
  • Plant returns must be treated like buy-ins.  Do not allow plants returns that have been commingled with host plants from another nursery. Trucks delivering buy-ins must be free of plant debris before entering the nursery.  The trucks must unload directly into the isolation area or, if a common loading dock is used, the loading dock cleaned of all debris after unloading. Maintain records of buy-ins (quantity and sources), location of isolation area, and inspection records for a minimum of 12-months.

3. Adopt the following practices for host plant nursery stock on hand. 

  • Train nursery personnel on appropriate worker sanitation, inspection, and sample collection procedures.Personnel working with host plants must be trained on the cleanliness program requirements.  
  • Maintain training records, including names of attendees and trainer, date, and subject matter, for 12-months.  Training materials are available from the American Nursery and Landscape Association (www.boxwoodblight.org).
    • Scout stock frequently for the disease.  The fungus is active between 41° and 90° F; optimal temperatures for disease expression fall between 64° and 77° Fahrenheit.
    • Host plants in production areas must be inspected monthly. Samples must be collected from plants exhibiting suspicious symptoms and tested for Cylindrocladium pseudonaviculatum by a laboratory acceptable to the Department.
    • Records of test results must be maintained for 12-months from the time of issuance.
    • Separate blocks of host plants by a minimum of 2-meters (6-feet).  The 2-meters may be open space or plants of non-host genera and species.
    • Maintain copies of all pesticide applications as required by the Federal Pesticide Recordkeeping Regulations from the 1990 Farm Bill.
4. Adopt the following practices for sanitation.
  • Remove and destroy leafy debris at least monthly from blocks of host plants, including debris from pruning.
  • Sanitize pruning tools and other equipment regularly between cultivars or blocks of plants.
  • Avoid overhead watering to minimize leaf wetness.  Alternatively, conduct watering so as to allow leaves to dry before nightfall.
  • Minimize standing water in the isolation area and host plant production areas.
  • Monitor host plant debris in water run-off.  Minimize water run-off out of the host plant productions areas.
  • Remove all crop debris and disinfest the production area, machines, and tools after every crop production cycle .  Use new, sanitized, or thoroughly cleaned containers for host plant production.  Do not re-use potting media unless it has been sterilized.


5. Agree to perform the following should C. pseudonaviculatum be detected within host plants located on the nursery. 

  • Report positive detections to the ODA. 
  • Use trained workers to determine the extent of the infestation and to remove and destroy infected plants as described below.
  • Remove and destroy infected plants and healthy-appearing host plants located within 2-meters (6-feet) of the identified infected plants.  This is the destruction block.  
  • Destruction must be by burning to ash or deep burial. Remove and destroy as described above any host plant debris from areas where infected plants have been found. Surface sanitize the soil under infected plants.  Alternatively, and after removing as much plant debris as possible, the nursery may put a new weed barrier in place and cover the weed barrier with a minimum of 4-inches of new gravel. 
  • Sanitize pots/containers, trays, benches, propagation and production areas, tools, and equipment before re-use. Monitor all host plants located within 10-meters (30-feet) of the destruction block weekly for suspicious symptoms.  These plants must not be treated with fungicides active against Cylindrocladium species and may not be moved.  Plants that remain free of disease symptoms for 30-days following plant destruction may be moved. 
  • Record all activities on an inspection form.  The inspection form may follow the standard format for the nursery.  Maintain records of all activities for 12-months from the time of plant destruction.
6. Maintain shipping records, including dates, quantities, plant shipped, and destinations, for a minimum of 12-months.
7. Allow the ODA access to the nursery to conduct inspections and, if necessary, collect samples to test for the presence of C. pseudonaviculatum.  Samples will only be collected if suspicious symptoms are observed.  The nursery will be responsible for all fees related to testing of officially collected samples.
8. Allow ODA to audit all necessary records and protocols to ensure compliance.  Interviews of employees may also be conducted to ensure compliance with training requirements.

If your nursery is interested in participating in this compliance program or you require additional information, please contact the ODA, Plant Division, Nursery Inspection Program (503-986-4644) or your area ODA Horticulturist.