Boxwood Blight
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Boxwood Blight

Updated 12/5/2018

Boxwood blight is a disease affecting several host plants including all Buxus species to varying degrees, with B. sempervirens being more susceptible. Other hosts include plants of the genera Pachysandra and Sarcococca. It is caused by Calonectria pseudonaviculata, a soilborne pathogen.

The pathogen that causes boxwood blight can be transmitted

  • through the movement of infected plant matter, including cuttings, leaf debris and whole plants
  • through contaminated landscape and garden tools and workers
  • through rain or irrigation splash

Boxwood blight has been confirmed in 27 states. Two states, Pennsylvania and Tennessee, have established boxwood blight quarantines. In most other states, boxwood blight remains a disease of great concern. Several Oregon nurseries have been greatly impacted by boxwood blight.

We have assembled this collection of resources for member growers so they can be informed about boxwood blight and have tools available for dealing with this disease threat, should they produce or handle any of the named host plants at their facilities.

The Oregon Association of Nurseries (OAN) asks for your assistance in identifying high-priority research needs aimed at helping the nursery industry to produce and ship disease free plants. If you have ideas, please contact Jeff Stone at jstone@oan.org.

Primary Resources:

Articles:

Here are some useful articles on boxwood blight and box tree moth aka box tree caterpillar. If you become aware of other articles that are worth sharing, please send the link to Curt Kipp, OAN director of publications and communications, at ckipp@oan.org. Information will be shared here at OAN's discretion.

» Pacific Northwest Plant Disease Management Handbook: Boxwood Blight — Comprehensive guide including description, symptoms, scouting and control measures.

» Disease hitting boxwood shrubs in Oregon gardens, by Kym Pokorny, Oregon State University Extension Service. June 2015.

» An invasive moth is reported in Ontario, Canada for the first time

Web

» Status of Boxwood Blight in Oregon — Video by Oregon State University Extension Service. Presented by Dr. Jay Pscheidt and Cassie Bouska. Part of the 2017 Oregon Master Gardeners Advanced Training series. Boxwood blight continues to be a problem in more landscapes and nurseries in the PNW. Learn about where this fungal disease has moved to, how to recognize it from other disease problems and run a model to determine when it might show up. Master Gardeners are our first responders to help limit the impact of this threat to our boxwood plantings. 50 minutes.

» National Plant Board: Plant Protection Laws and Regulations — Online resource listing current plant regulations, laws and quarantines. Searchable and updated regularly.

» ODA Boxwood Blight information page — Web page with information about boxwood blight.

Downloads

» Boxwood Blight Resource Sheet — Basic primer on boxwood blight, produced by AmericanHort and the Horticultural Research Institute (HRI). February 2018. Two pages. (PDF)

» Boxwood Blight Best Management Practices — Voluntary measures growers can take to manage the risk of boxwood blight introductions, and respond if the disease is confirmed on nursery grounds. Produced by AmericanHort, the Horticultural Research Institute and the National Plant Board. Revised September 2017. Four pages. (PDF)

» Beware of Boxwood Blight! — This concise publication from Oregon State University Extension gives useful information for homeowners, master gardeners, and professional landscapers about the boxwood blight disease: its symptoms, sanitation measures when it is discovered on a property, and preventive measures. Four pages. (PDF)

» ODA Fact Sheet: Boxwood Blight. — Brief rundown of symptoms, transmission and geographic distribution. Two pages. (PDF)

» Exporting Plant Material Out of Oregon — A list of current plant quarantines imposed by other states, compiled by the Oregon Department of Agriculture Plant Division. Revised February 2018. Four pages. (PDF)

» ODA Boxwood Blight Cleanliness Program — The Oregon Department of Agriculture (ODA) has a boxwood blight cleanliness program offering voluntary practices to prevent spread of the pathogen. The program results in certification for shipping into other states, particularly those that have quarantines in place. Tennessee is one such state. If you have questions, contact Gary L. McAninch, nursery and Christmas tree program manager with ODA, at 503-986-4644, or talk to any ODA horticulturist. Program information: Four pages. (PDF)

» Boxwood Blight in Commercial Nursery Production — Poster that prints up to 24 x 36 inches. (PDF)

» Susceptibility of Commercial Boxwood Cultivars to Boxwood Blight — Study from North Carolina State University Cooperative Extension. Three pages. (PDF)

Meetings:

On October 30, 2018, the Oregon Association of Nurseries (OAN) hosted an informational meeting on boxwood blight at its office in Wilsonville, Oregon. The presenters included representatives from the OAN, AmericanHort, the USDA Agricultural Research Service, and the Oregon Department of Agriculture. They discussed the current boxwood blight situation in Oregon and nationally. Below are summaries of the presentations. Watch this page for information about any future meetings regarding boxwood blight, or read the OAN Member Update to stay apprised.

Gary L. McAninch
Nursery and Christmas tree program manager, Oregon Department of Agriculture, Plant Divison
503-986-4644, gmcanininch@oda.state.or.us

Boxwood blight was first discovered in North America early in 2011 in North Carolina and Virginia. The first Oregon detection was made at a Washington County nursery in November of 2011. Each year since 2011, a limited number of Oregon nurseries and landscapes have been found infested with boxwood blight. Eradication procedures were enacted at each infested nursery.

The Oregon Department of Agriculture (ODA) is routinely asked to conduct "trace-back" inspections at Oregon nurseries that shipped boxwood plants to other states and these plants were subsequently found infected. In some cases the trace-back inspections do find that the Oregon nursery is the source of the infections. In many cases, ODA inspections do not find the disease at the nursery of origin in Oregon. The source of the infection remains unclear in these cases.

In 2012, the ODA imitated a Nursery Cleanliness Program for Boxwood Blight. The program's goal is to assist nurseries in shipping boxwood blight stock that is free of the disease. The programs best management practices are designed to:

  • void introduction of the disease onto the nursery,
  • detect the disease early if introduced onto the nursery. This is accomplished through timely inspections conducted by trained nursery staff.
  • minimize the spread of the disease at an infested nursery, and
  • eradicate the disease from infested nursery.

There are currently 35 Oregon nurseries participating in the Nursery Cleanliness Program for Boxwood Blight. Better disease detection tools for field use are needed.

Jerry Weiland
Research Plant Pathologist
USDA Agricultural Research Service, Corvallis, Oregon

My USDA-ARS research program is based on identifying soilborne pathogens of the nursery industry and improving methods for disease control. I have a horticulture background with an emphasis in woody plant production, as well as extensive experience in plant pathology. I am based in Corvallis, Oregon and am looking forward to helping out the industry address their concerns about boxwood blight.

There is a perception that Oregon is a source of infection for the boxwood blight pathogen. What research needs to be conducted to solve this problem? How do we conduct and report research results responsibly? For initial research I recommend the following:

  1. The first major issue is to find out whether there is asymptomatic (latent) infection of Oregon boxwood. In other words, is the pathogen present on Oregon boxwood, but not causing disease? How do nursery managers and inspectors know if there is a problem if there are no symptoms? How should we be sampling for this disease if there is latent infection? I would like to visit nurseries and sample plant material this coming fall/winter to begin to answer these questions.
  2. Are our boxwood blight pathogen strains different than those present in the eastern part of the U.S.? This may help answer whether Oregon is a potential source of the pathogen (or whether Oregon received the pathogen from other states) and how the pathogen might move through interstate trade.
  3. Does our Oregon environment (warm, dry summers with cooler nights) prevent disease from becoming as severe as in the eastern U.S. (hot, muggy summers)?

What other research is important to boxwood growers?
What else can we do to show that we are being proactive?

Jill Calabro
Science and research programs director, AmericanHort and the Horticultural Research Institute
202-789-0683, jillc@americanhort.org

Some 27 states and the District of Columbia have confirmed positive diagnoses of boxwood blight. The disease spread is facilitated by movement of infected plant material. The possibility of latent infections is unknown with boxwood blight and needs to be explored.

Diagnosticians are reporting record number of boxwood blight finds in 2018. This could be due to conducive weather conditions and/or heightened awareness of the disease. The industry could benefit greatly with a researcher positioned in Oregon to act as a resource.

HRI has started a new project aimed at creating a standardized testing protocol for boxwood blight and then to compare cultivars in terms of their level of tolerance or susceptibility. The first round of cultivars (18) has begun. The research is being conducted in Connecticut.

On a related note, the box tree moth may have been found in the Toronto area. It would be the first finding in North America, but it remains unconfirmed at this time. The industry needs to be on alert.

A related pest concern: box tree moth

» New Pest Response Guidelines — A guide to screening, control and management of the box tree moth (Cydalima peerspectalis), an insect pest that is hosted by boxwood species (Buxus spp.). The pest has become established in Europe but not the United States. There was a sighting in Ontario, Canada in September, 2018. Published by the USDA Animal and Plant Health Inspection Service (APHIS) Plant Protection and Quarantine program. First Edition published 2017. (PDF)