Restoring Gardens Affected with Boxwood Blight

One of the most common questions gardeners and landscapers face after having dealt with a Boxwood Blight infection is if it is safe to re-plant boxwood? Because there are many factors to consider, it can be a tricky question to answer with certainty. Luckily NewGen® had the opportunity to partner with a research team from Virginia Tech on a project to determine how more resistant boxwood cultivars may perform at a recently infested landscape site after diseased plants and debris have been removed.

Blighted boxwood shrubs, January 2019.

The property where the experiment is currently taking place is a 30-year-old residential garden located outside of Richmond, Virginia. This garden had over 400 well-established boxwood, mostly American (Buxus sempervirens) and English (Buxus sempervirens ‘Suffruticosa’). Some boxwood were surrounded by perennials and ground covers such as Pachysandra, another known host for Boxwood Blight. The garden borders a native forest with large trees, leading to deer and other wildlife regularly moving throughout the property. 

The connection between the homeowner and the researchers at Virginia Tech began in late 2015 after the homeowner came back from vacation in August to find some of her boxwood infected with Boxwood Blight. After speaking with an Extension agent to confirm the disease, the agent connected her with Dr. Chuan Hong, Professor of Plant Pathology at Hampton Roads Agricultural Research Center.

Dr. Hong and his team have since performed a series of research projects to better understand Boxwood Blight. Of the most practical were mulching trials. Those trials were essential to extending the benefits of mulch for Boxwood Blight mitigation.

Gated garden where the trial took place. Dark black spots are location where previously infected boxwood existed and have since been removed and the ground flamed to reduce soil inoculum.

In early 2019, Dr. Hong began a new research project focusing on restoring the boxwood garden with more resistant cultivars as a major component, along with several other innovations. Bennett Saunders, Dr. Hong, and others evaluated the site in early March of 2019 to make plans for the “New Garden” project which would take place in a gated section where all large boxwood shrubs were destroyed.

Bennett Saunders, Dr. Hong and the research team evaluating the site in March of 2019.

A truck load of NewGen Independence® ready to be planted in May of 2019.

Later that month Dr. Hong and his team began the clean-up step. This included removal and burning of aboveground parts of the plants, followed by flaming fallen leaves and debris with propane torches and then digging and removing all stumps. In May of that same year, the garden was replanted with NewGen Independence® along four sides of the central square, and NewGen Freedom® along the fence. Immediately after replanting, soil surface underneath and surrounding each NewGen boxwood was mulched to prevent the Boxwood Blight pathogen moving from the soil onto plant foliage by water splash. A weather station, plus two soil moisture probes, were also installed to gather on-site environmental data to determine whether preventative fungicide sprays were needed. When needed, every other Independence boxwood was sprayed preventatively, while the other boxwood were left as nontreated control plants.

Layout of New Garden trial.

Although the experiment is still on-going, early results have been very promising! As of September 2020, all the plants have been through the better part of two Boxwood Blight seasons and are showing no symptoms of Boxwood Blight regardless of fungicide protection. All plants are evaluated regularly, and fungicides are only sprayed when weather conditions are very conducive to the disease.

NewGen Independence® showing no symptoms of Boxwood Blight a year and a half after being planted.

NewGen® believes that the future of boxwood combines best management practices and more resistant boxwood cultivars. Early results of this trial confirm that message! The future of boxwood is bright, and this beloved shrub will continue to grace landscapes and gardens for generations to come.

A clean NewGen Freedom® continues to perform in the landscape, showing no signs of Boxwood Blight.

Cleaning Up Boxwood Blight in the Landscape

Late summer through mid-fall is the most likely time to see Boxwood Blight in landscapes.  Shorter days, splashing rains, ideal temperatures from 60°-77° F, and slower drying create an environment in which the disease thrives. Be on the lookout!

Since 2011 when Boxwood Blight was first discovered in the United States, there has been a great deal of research and much has been learned regarding control and living with the disease. The earliest assumption was that any landscape infected by Boxwood Blight would need to be destroyed, however; research has shown there are many steps that can be taken to clean up Boxwood Blight properly. If certain steps are taken early, many landscapes of Buxus sp. can survive and even thrive after Boxwood Blight.

Rubber boots are easily cleaned after being worn in landscapes containing boxwood.

If Boxwood Blight is suspected:

• Take samples to testing labs and limit access to the area until results are obtained.

If you suspect the disease in the landscape, you should take great care in collecting samples by double bagging them and taking them to the local Extension office or another testing lab. The area should be roped off or temporarily fenced off until the results are obtained.

If Boxwood Blight is confirmed:

• Take great care not to further spread disease.

• Do cleanup on dry, sunny days when foliage is dry.

• Consider fungicide applications before and during cleanup to control spread.

• Wear rubber boots and disposable clothing during cleanup to lessen contamination of clothing and shoes.

• Cut and place the infected plants in a plastic bag and take care to minimize leaf litter.

• Clean up as much leaf debris as possible. Roots are not believed to carry Boxwood Blight.           

• Debris should be burned or taken to landfill with care to not let leaves escape.

• After cleanup, wash skin, launder or dispose of outer clothing, and wash boots.

• Increase airflow in and around remaining plants by thinning and removing lowest limbs.

• Do not bury debris as the disease can survive in the soil for long periods of time.

• All tools and equipment should be thoroughly cleaned when moved between different gardens or areas.

• Mulch to lessen the splashing of spores.

• Replant with cultivars that are more resistant to Boxwood Blight.

• Monitor boxwood in times of optimal conditions for new infections and flare-ups.

Crews at Saunders Brothers, inc. wear disposable clothing to help avoid introduction of Boxwood Blight that may enter the nursery on their clothing.

If Boxwood Blight is confirmed, you must be diligent and careful in cleanup. Extreme care should be taken to avoid infecting other plants. Choose a time to cleanup when it is sunny and when foliage is dry. The plant is less likely to be sporulating when foliage is dry. Consider applying fungicides to any area where you are working to kill any spores that are present.

Always wear some sort of disposable suit, like disposable Tyvek® coveralls, and rubber boots as they can easily be cleaned. If possible, put a plastic bag over the infected plant and cut the plant off at the base. Take care to catch as much leaf litter as possible. Then, clean up any leaves that fall before disturbing the soil as you do not want to incorporate diseased debris into the soil. After all debris is cleaned up, remove the roots. All debris should be bagged or covered to eliminate the possibility of it blowing or falling out. Do not compost the debris. Burning the debris is the best possible option.

The most effective way to sterilize soil is to burn any debris around the base of the infected plant.

After the cleanup is complete, remove outer clothing and launder or dispose of it. Laundering with detergent and hot water will kill spores. Boots should be thoroughly washed, and all tools and equipment should be carefully cleaned as well. Prune any other boxwood in the landscape to increase airflow to maintain dry foliage. Remove any limbs that touch the ground and might get rain splash, and be sure plants are properly mulched. Continue to monitor the boxwood during environmental conditions conducive to infection.

If planning to replant with boxwood, be sure to choose cultivars that are more resistant to the disease. Saunders Brothers, Inc. and Saunders Genetics have tested and trialed boxwood in search of varieties and cultivars that prevail against Boxwood Blight.  Buxus sempervirens ‘Suffruticosa’ (English boxwood) is the most susceptible cultivar, whereas Buxus microphylla, Buxus insularis, and Buxus harlandii species and cultivars tend to have more resistance. It is difficult to completely define groups based on species as we have found exceptions based on plant architecture and structure. Open, more upright plants tend to be less susceptible while short, compact cultivars seem to be more susceptible. NewGen Independence® and NewGen Freedom® offer strong resistance to Boxwood Blight as well as fantastic landscape appeal.

Once the landscape is cleaned and replanted, diligently monitor plants to catch any early signs of re-infection. With a combination of careful clean up, replanting with resistant cultivars, and best management practices to avoid Boxwood Blight, landscapes of Buxus sp. can continue to flourish after Boxwood Blight.

NewGen Freedom® in the field.

Feb. 2020: Third International Summit on Boxwood Challenges

The NewGen™ and Saunders Brothers teams at the Third International Summit on Boxwood Challenges, hosted by the American Boxwood Society.

Last month the American Boxwood Society hosted its Third International Summit on Current Boxwood Challenges. Over 140 people heard from researchers and growers from Europe, Canada and the United States who discussed the latest research on Boxwood Blight and the Boxwood Tree Moth. This one-day event was hosted at the National Agricultural Library in Beltsville, Maryland.

Although the Boxwood Tree Moth has not been found in the United States, it has devastated boxwood production in Europe. The morning session of the event began with research on the biology of the moth, determining the invasive pathways that introduced the moth to Europe, concluding that the pest was originally introduced from eastern China to Germany in 2007 and has since spread significantly over Europe. Most of the spread has been from the transport of infected plant material, with some movement through native boxwood forests. The moth was found in the United Kingdom in 2008 and has since spread around the southern parts of the country. Chris Poole, the Chairman of the European Boxwood & Topiary Society, shared management strategies being utilized in the United Kingdom and around Europe against the moth.

The morning session finished with speakers from North America, focusing on what the Canadian industry is doing to monitor and prevent the spread, and how the U.S. can prepare against the moth. First identified in Ontario in October 2018, OMAFRA (similar to U.S. Extension) has diligently been monitoring and treating the pest as it appears. Using many of the same tactics that have been effective in Europe, most infections are low to moderate, with less than 10% considered severe. In the United States, using pheromone traps for detection and diligently spreading the word about this potentially invasive species can aid in catching the moth early. In the event that it is found, there are methods of control already available. Researchers are aware of the pest and are focusing efforts to learn from those already affected in order to prevent the introduction of Boxwood Tree Moth to the United States.

The afternoon focused on Boxwood Blight starting with a recap of what is known about the disease and ways to treat and prevent it. Mary Ann Hansen, who works in the Plant Disease Clinic at Virginia Tech, has many years’ experience identifying Boxwood Blight. She shared information about the biology of the disease, how to identify it, and how to clean it up in the event of an infection. There are many tools available to the public about Boxwood Blight, including the Virginia Boxwood Blight Task force website.

The event finished with several presentations on further research being done around the U.S. There are many projects in the works focused on learning new and effective control strategies. Projects range from breeding programs to biocontrol studies to thermotherapy, all being done at many universities around the U.S. There is still no silver bullet in preventing or treating Boxwood Blight, but the is a light at the end of the tunnel as much of the research proves positive. One of the recent studies showed a decrease of Boxwood Blight lesions by 97% just from adding a layer of mulch. You can read more about that study here. As research continues, we only get more positive that as an industry we can overcome this challenge.

If you’d like to learn more about events like these, check out the American Boxwood Society’s website.

Dec. 2019: Boxwood Blight Update

A field of boxwood affected by Boxwood Blight.

Since its introduction to the United States in 2011, boxwood blight has been found in 26 states. Its affects have been seen from the Mid-Atlantic to the west coast in varying degrees. One of the biggest contributing factors to the prevalence and spread of this disease is climate. Boxwood blight requires specific environmental conditions which vary year to year. This fungal disease spreads by spores that move by water splashing, physical contact, or on debris. Infections occur during humid, warm periods, and can spread quickly when conditions are ideal.

The map above shows states with reported cases of Boxwood Blight by year.

Characteristic symptoms of Boxwood Bight include dark streaking on the branches, leaf spots, and defoliation.

As many growers recall, 2018 was a devastating year, especially in the Mid-Atlantic. With record breaking rainfall and extended periods of warm, wet weather, many growers, landscapers, and homeowners saw more cases of the disease than previous years. Mary Ann Hansen, who oversees the Virginia Tech Plant Disease Clinic reflects, “In 2018 when we had so much rain across the state, the VT Plant Disease Clinic received 188 boxwood samples that were positive for boxwood blight. This amounted to over 11% of our sample total.”

Bennett Saunders next to the Tye River at record high levels in September 2018 after another heavy rain storm.

In Piney River, VA we saw over 90 inches of rain throughout the year, compared to the annual average of about 45 inches. Reports of flooding and extended rain events throughout the spring, summer, and fall were followed by reports of infection.

Juxtaposed to the previous year, 2019 has been uncharacteristically dry, leading to fewer cases. Mary Ann from Virginia Tech reports, “In 2019, we only received 44 boxwood samples that were positive for boxwood blight, and this amounted to less than 3% of our total samples. The number of samples received by the Clinic doesn't necessarily represent the amount or severity of the disease across the state, but in this case, I think it probably did. The weather in 2018, especially in the fall, when boxwood blight tends to be a problem, was very conducive to boxwood blight, whereas the long drought and high temperatures in many areas of the state in 2019 were not conducive to boxwood blight. The fungal pathogen, Calonectria pseudonaviculata, does best at moderate temperatures with extended periods of leaf wetness.”

It is important to keep in mind the effect the environment can have on the spread of plant diseases. For more information on Boxwood Blight and how to prevent it, check out the Virginia Tech Boxwood Blight Task Force website or read more about it here.

Tips and Tricks for Growing Cleaner Plants

Creating a phytosanitary plan doesn’t have to be a daunting endeavor. There are many simple steps you can take to grow cleaner plants. Saunders Brothers has worked with many researchers and Extension agents to establish protocol to help prevent the introduction and spread of Boxwood Blight at their nurseries. Although this plan was designed with Boxwood Blight in mind, these practices will help growers produce cleaner, more successful plants.

Foot mats/baths:

Foot baths are located at every walkway leading to the Saunders Brothers office.

One of the first and easiest steps to take is the inclusion of foot mats/baths for sterilizing shoes of anyone entering a growing area. These can be placed in greenhouses, worker common areas, and near offices. Having foot baths as a first line of defense minimizes the introduction of new pathogens to your growing area. Saunders Brothers uses foot mats at the entrance to all of their office and worker areas. Saunders Brothers uses Zerotol® 2.0, but a 10% bleach solution is also effective.

Disposable pant/boot covers:

Crews in the field nursery wear disposable suits when they are working on larger plants.

Crews wear rubber boots that can be easily cleaned and disposable pants when moving between growing areas.

An example of plastic pant and boot covers in the field.

Disposable pants and boots serve as a physical barrier between one’s clothing and the plants they are working in. If there are any spores or pests on the clothing, it is less likely they will migrate to the plants. Saunders Brothers employees wear disposable, plastic pant and boot covers while working in boxwood houses. Boxwood Blight spores can stick to tools and clothing moving from location to location, so instead of worrying about having fresh clothes, disposable pant/boot covers are the perfect solution.

This is also a great tool for landscapers that may visit many sites in a day. Instead of having to change or sterilize clothing, wearing disposable pant and boot covers greatly reduces disease or pest movement from site to site.

Sterilizing tools/equipment:

Pruning crews as Saunders clean their tools with alcohol between each house.

Even large equipment like digging machines are cleaned with sterilant between fields.

Sterilizing tools and equipment is an easy, practical step to take towards growing cleaner plants. It is a good practice to carry around a spray bottle of isopropyl alcohol. Research shows that a 50% isopropyl alcohol solution is effective at killing most plant diseases. Alcohol spray can be used to clean any handheld tools such as pruners, shovels, or trimmers. Other options of sterilants are a 10% bleach solution or Lysol® spray. Many researchers also recommend hydrogen dioxide products such as Zerotol® 2.0. Make sure to always check labels before you use any products. Most of these products are very user-friendly and are labeled to clean tools, equipment, or even surfaces.

Dragging a hose through a bed of infected plants and then moving it through a healthy bed could spread diseases. Taking an extra minute to spray the hose down with a sterilant could avoid a bigger cleanup in the future.

Cleaning Stations/Sectioned growing areas:

Cleaning stations in the field nursery.

Cleaning station in the container nursery.

This tip takes a bit more planning than some of the other suggestions, but might have the biggest pay off if you ever run into a disease or pest problem. Saunders Brothers has set up both their field and container nurseries in sections. In the container nursery, boxwood are grown in specific locations separated by roadways. In the field nursery, areas are sectioned based on geography. Each section has a cleaning station that all employees must visit at they enter and exit. Cleaning stations are stocked with:

• Disposable pant/boot covers

• Trashcan

• Boot bath and brush

• 70% Isopropyl alcohol spray/liquid hand sanitizer.

• High pressure water hose (field)

Crews using a cleaning station to rinse off their shoes and equipment.

Upon entering and exiting the area each employee must:

Entering:

• wear rubber boots, easily washed boots, or disposable boot covers

• step in boot bath/wash boots

• put on disposable pant covers

Exiting:

• remove and trash disposable pant covers or spray pants

• step in boot bath/wash boots

• wash hands/ use hand sanitizer

• rinse off tools, then spray with alcohol

This is an example of the sectioned boxwood production areas are at the containers nursery at Saunders Brothers.

The perks of setting up these sectioned areas is that in the event of an infection, you can quarantine one area, and continue production from the other locations. Consequently, each time a person or a crew enters a new area, they are cleaning off any potential pests or diseases.

Establishing cleaner growing protocol doesn’t have to be a daunting task. Taking some steps early on in production can help set you and your plants up for success while combating common pests and diseases. Consider these tips and find what works for you.

The Story Continues

The Saunders Family

Growing up a Saunders predisposes you to have a certain affection towards boxwood. In our previous post we told the story of Paul Saunders and how he turned his passion for boxwood cultivation into a successful family business. Saunders Brothers Nursery began growing boxwood over 70 years ago and this was just the beginning. As the business has transitioned to a new generation of leadership, Paul’s sons, Robert, Bennett, Tom, and Jim reflect on their memories from sticking boxwood cuttings to earn an extra penny, to the discovery of Boxwood Blight in the United States and, to the creation of the NewGen™ program.

From an early age, the sons participated in every part of boxwood production around the farm. Bennett Saunders, General Manager of Saunders Genetics, remembers, “As kids, we would get paid a penny apiece for each boxwood cutting we stripped and stuck. This is how we would earn our extra spending money.” As the boys grew, they continued to play an essential part in the daily farm responsibilities. “I remember spending most weekday evenings at the nursery loading trucks with boxwood from March to May,” recalls Bennett. “At the time, boxwood were about 40% of the plants we grew.”

Boxwood Decline affecting English boxwood in a landscape

One of the first setbacks in boxwood production came about in the 1970s with the advent of Boxwood Decline. Up until this point, most of the boxwood market was made up of English boxwood (Buxus sempervirens ‘Suffruticosa’). As Boxwood Decline became more prevalent, the company began to move towards a wider selection of boxwood cultivars that were more resistant to the disease. Robert Saunders, General Manager of Saunders Brothers remembers, “In the spring of either 1981 or 1982, I was in high school and I got a note from the principal’s office saying I needed to call home. I called and my dad explained that he wanted me to come home to see an experiment he was doing. He was planting in an area just outside the yard at our house, a test garden of new varieties of boxwood. At that time, we grew only English and American boxwood, but my dad thought we should try some new ones.” Robert was dumbfounded for two reasons, “Number one, I hated plants, so I did not want to have anything to do with it. Number two, why did we need new varieties of boxwood? Little did I know I would end up working in the middle of it. From those trials, an evolution of perspective began and, we soon found Green Beauty, Green Velvet, Green Mountain and many other varieties. Most importantly it taught us about life beyond our small boxwood world.”

The exploration into new varieties of boxwood began to shed light on another lurking boxwood pest. “There was a field planting of Buxus sempervirens ‘Elizabeth Inglis’ that had just been eaten up with Boxwood Leafminer,” Bennett remembers. “It had never been sprayed and was just covered in blistered leaves.” Deciding this might be something worth exploring, they planted some other varieties near the host plant to see if different cultivars showed any natural resistance to the pest. Early observations showed that there was some hope for these different cultivars which encouraged Saunders to pursue more formal research.

Boxwood Leafminer larvae causing the boxwood leaves to swell and blister.

Dissecting boxwood leaves to count larvae.

In the early 2000s, Boxwood Leafminer incidences started to become more prevalent, coinciding with a general desire to reduce the use of pesticides, particularly the neonicotinoids. Saunders Brothers recruited retired nematologist Bob Dunn from the University of Florida to help them set up a replicated plot to collect data. They began by planting a test block where host plants infected with Leafminer were planted alongside many different cultivars of boxwood. Since the fall of 2006, thousands of leaf samples from the test area have been collected. Each leaf was dissected, and larvae were counted. The collection of this data over a decade showed a strong variation of cultivars’ natural resistance to Leafminer. This in turn meant a reduction in the use of pesticides and an increase in the value of boxwood in today’s gardens.

Bob Dunn, retired nematologist, working on Boxwood Leafminer research.

Boxwood Blight affecting a field nursery.

Then, in the fall of 2011, Bennett recalls that, “we began to hear horror stories about a disease called Boxwood Blight which was devastating boxwood nurseries in North Carolina and Connecticut. We called a meeting the Monday after Thanksgiving to decide what to do. We decided we needed to go to Europe before the MANTS show to have more information to better answer customers’ questions. We immediately bought tickets for a team from Saunders to go to Europe the week before Christmas. My wife was not happy, but it was something we had to do.”

Researcher in Europe showing examples of Boxwood Blight.

Bennett Saunders loading a truck with sample plants for NCSU trials.

Since the disease had been prevalent in Europe since the mid-1990s, members of the Saunders team spent time in Belgium and the United Kingdom to learn tactics to combat it. European researchers mentioned that they had seen that genetic tolerance for the disease varied among boxwood species. Saunders realized that trials could be performed, similar to the Leafminer trials, to discern genetic tolerance. In 2012, Saunders Brothers teamed up with Kelly Ivors at North Carolina State University to begin trialing different boxwood species and cultivars. Thanks to years of collection, many different boxwood cultivars existed at the nursery in Virginia, so Saunders sent samples of these varieties to be part of the trials. This research proved to be so insightful that after the research was completed at NCSU in 2015, Saunders continued the trials privately. It was clear this was a challenge that could be overcome.

Kelly Ivors (middle) and team at NCSU.

NewGen Independence® in field trials.

 Since learning about the disease, enormous resources have been dedicated to learning about Boxwood Blight. Saunders Brothers has donated thousands of plants, given input into multiple research projects, and made every attempt to better educate themselves and the growing community about this disease. Teams have traveled domestically and internationally to better understand a disease that many once thought would be the end of boxwood. Working with researchers from state and federal agencies, as well as international groups, the continued message was apparent that through a greater understanding of the disease, the battle with Boxwood Blight will be won with tolerant varieties and best management practices.

NewGen Freedom® in production.

Holding on to that message of hope, and after years of trialing, certain cultivars continued to outperform many of the popular varieties on the market. Two of those cultivars were chosen because they stood out from the rest. “These plants showed up and made us smile and think ‘We’ve really got something here’ that we can share with the industry,” remembers Robert. The discovery of these beautiful plants characterized by their superior resistance to Boxwood Leafminer, high tolerance of Boxwood Blight, and WOW factor in the landscape led to the creation of the NewGen™ brand. You can read more about that story here.

From one 13-year-old boy’s love of a charming little evergreen grew a family business dedicated to innovation and looking for solutions. Saunders Genetics, LLC was created to become a resource for all boxwood enthusiasts for generations to come. With over 70 years’ of experience and a passion for boxwood, they are excited to introduce a new generation of boxwood to the industry.

Paul Saunders and his wife, Tatum, at their home.

Fungicide Recommendations for Boxwood Blight in Virginia

By: Dr. Keith Yoder - Retired Plant Pathologist, Virginia Tech

Following the severe boxwood blight year in the Mid-Atlantic region in 2018, nursery growers and landscape care professionals should diligently follow prescribed Best Management Practices (BMPs) as a first line of defense to avoid introducing the boxwood blight fungus or, where blight is already present, to manage it most effectively while reducing the risk of spreading it to new locations.

Fungicides are an essential part of the BMPs. They protect boxwood and reduce the spread of blight by preventing germination and infection by the fungal spores. Examples of protectant fungicides listed in the Virginia Tech Nursery crops Pest Management Guide (PMG, page 5-7) are chlorothalonil (Daconil Weather Stik, 1.4 pt/100 gal) and mancozeb (Dithane 75DF Rainshield 1.5 lb/100 gal). Some fungicides are locally systemic (within the leaf) and offer specific modes of action. Recommended examples, also listed in the PMG, include fludioxonil (Medallion WDG2-4 oz/100 gal), thiophanate-methyl (Cleary 3336 WP 1.5 lb/100 gal), boscalid + pyraclostrobin (Pageant 12-18 oz/100 gal), and tebuconazole (Torque 10 fl oz/100 gal). Because the systemic classes of fungicides tend to be at risk for development of resistance, it is generally recommended (and often specified on the label) that they should be alternated and tank-mixed with broad-spectrum protectant fungicides such as chlorothalonil or mancozeb. Spectro 90WDG (1.5 lb/100 gal) is a combination product that contains both chlorothalonil and thiophanate-methyl. The above list is provided as recommended examples. We feel these can be blended into an effective season-long program, but this list is not meant to exclude similarly labeled formulations and other effective products.

In practice, a rotational schedule of very effective fungicides containing both protectants and systemic products that would have minimal chance of developing resistance might look something like this:

Week 1: Chlorothalonil (Daconil Weather Stik, 1.4 pt/100 gal).

Week 3: Mancozeb (Dithane 75DF Rainshield 1.5 lb/100 gal) + Tebuconazole (Torque 10 fl oz/100 gal).

Week 5: Chlorothalonil (Daconil Weather Stik, 1.4 pt/100 gal).

Week 7: Mancozeb (Dithane 75DF Rainshield 1.5 lb/100 gal). + Pyraclostrobin (Insignia 8-16 oz/100 gal).

Week 9: Start back with the Week 1 rotation. If need be, there are other classes of systemic fungicides that could be substituted into the rotation.

Fungicide applications should begin in the spring when conditions become favorable for infection: Infection periods occur at temperatures of 60-77°F with extended wetting and high humidity. The residual activity of fungicides is affected by amount of rainfall, weathering and degradation, and must be reapplied at regular intervals while the risk of blight infection is present. However, they must not be applied more frequently than recommended treatment intervals, or applied in excess of rates specified on the product label. Always read and follow product labels for safety instructions regarding mixing, handling, compatibility with other chemicals, application methods, re-entry intervals and limitations on amounts of product per acre per year.

Because blight spores can stick to tools, equipment, spray hoses, etc., sanitize all equipment, shoes, gloves, etc., used in tending and treating boxwood to prevent spread of fungal inoculum to healthy plantings. For a list of sanitizer recommendations, refer to the Boxwood Blight Task Force website. It is recommended that vehicles that may have been exposed to the boxwood blight fungus be thoroughly washed of debris (e.g. cleaned at a carwash) to avoid spreading the fungus from one planting to another.

A note about spray equipment: At Saunders Brothers we spray our nursery blocks with an “air-assisted” sprayer (pictured above). We chose this sprayer and like it because it gives good penetration of the spray by spraying straight down into the plants. Many airblast sprayers are characterized by the strong sideways airflow, which could blow detached leaves and plant debris from row to row, possibly spreading disease.

To be noted: While Saunders Genetics has worked with nursery growers who have successfully used the pesticides listed above, we make no guarantees or promises, nor express any opinions, concerning the effectiveness or safety of these or any other pesticides.  Always read the labels and other product information from the manufacturer and discuss the proper use and application of products with appropriate company representatives or acknowledged experts.

Basic Biology and Management of Boxwood Blight

Since Boxwood Blight was found in the United States in 2011, researchers and growers have been diligently working to understand this pathogen. Although the disease has spread to 28 states since its initial identification in North Carolina, there have been many breakthroughs in the understanding of the biology of the disease and how to control it.

Map of states with known cases of Boxwood Blight as of 2018

Boxwood Blight is a fungal disease caused by the pathogen Cylindrocladium buxicola (syn. Calonectria pseudonaviculata). The pathogen attacks the foliage of boxwood, first appearing as black or dark brown spots on the leaves. In a few days, those spots will develop yellow to brown rings around them and cover the leaf. Infected leaves fall off the plant in a matter of a week or so, and stems near infected leaves will develop streaked black lesions or cankers.

The disease is most prevalent when environmental conditions favor warm temperatures between 60° - 80° F and high humidity. Leaves that are continually wet from constant irrigation, prolonged rain, or high humidity are prime targets for the pathogen. When conducive conditions subside, the fungus will go dormant in the form of black streaks in the limbs of affected plants or debris. The fungus can lie inactive for long periods of time and reappear when conditions become conducive again.

Here you can see the north side of the plant getting the disease first. There is almost an exact line because the north side gets less sunlight and dries more slowly.

The Boxwood Blight spore is heavy and sticky, and is typically introduced through contact with infected plants, debris, tools and equipment, clothing, animals, water splash, or other means of direct contact.

Currently, the only known hosts of the pathogen are members of the Buxaceae family, Buxus sp. (Boxwood), Sarcococca sp. (Sweetbox), and Pachysandra sp (Spurge).

With a better understanding of the disease lifecycle and its optimal conditions, there are many practical ways to prevent and control the spread.

Because the spores can spread from plant to plant on clothing, tools, or splashing water, anyone working around boxwood should start with clean clothes, shoes and tools. Make sure to properly clean tools and equipment with disinfecting agents like alcohol, bleach, or Lysol before and after use in boxwood. If you are a landscaper moving from site to site, you should use a disinfectant on clothing and shoes, or use disposable pant and boot covers between sites. Starting with and maintaining clean equipment can remove the pathogen from ever entering a new site. 

Spores of the pathogen can also spread through water so it is best to avoid overhead irrigation when possible. Facilitating an irrigation schedule that allows just a 3 hour period of dryness for the leaves can significantly reduce the spread of the disease. When there are periods of dry foliage, the leaves are far less likely to become infected, even if the spores are introduced. Never use overhead irrigation in the late afternoon because leaves will remain wet all night. Maintain good air flow when planting and pruning the plants to ensure leaf drying. Recent studies have also shown that mulching every two years or so with at least an inch of mulch around the base of the plant can lessen water splashing.

Studies have shown that, when tested in a lab, all boxwood cultivars show some susceptibility to blight. However, many field tests have shown significant differences in tolerance between cultivars. We have observed certain cultivars, particularly the microphylla, insularis, and harlandii species show strong tolerance compared to those with sempervirens genetics. Shape and structure of the boxwood also affect each plant’s tolerance. Open, more upright plants tend to be more tolerant while short, compact cultivars seem to be more susceptible. We believe this is because the shorter plants that are close to the ground get more water splashing on them. Research is ongoing to discover additional cultivars that will be tolerant to boxwood blight. 

A photo of Buxus ‘SB 108’ NewGen Independence™ next to an American Boxwood, planted on the same site for 3 years.

The exciting results we have seen with varietal tolerance inspired us to create the NewGen™ Boxwood brand. We believe the combination of tolerant varieties and best management practices like those we have outlined are the future of an industry that doesn’t fear Boxwood Blight. For more information check out our education page on Boxwood Blight and subscribe for monthly newsletters filled with the most relevant and up-to-date information and research on boxwood.

 More examples of Boxwood Blight damage and examples on how the pathogen moves:

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Who is NewGen™?

Easily one of the most recognized garden plants, boxwood (Buxus sp.) have been gracing formal gardens for thousands of years and are considered one of the oldest ornamental plants. As slow-growing evergreen shrubs, these plants have always been a symbol of a gardener’s commitment and investment to a green space. Boxwood have held their reputation for many years because they are low maintenance, provide structure to a garden, and have few pests and disease pressures.Unfortunately, this reputation took a hard hit in 2011 with the introduction of Boxwood Blight in the U.S. and many growers became concerned about the beloved plant.

Saunders Brothers in Piney River, VA, a family-run nursery with a rich history of boxwood production, responded to this threat by investing in research to find a solution. Their experience in trials for resistance to Boxwood Leafminer, helped them to work with researchers and universities to begin testing for varietal tolerance of Boxwood Blight. After testing over 150 varieties, it was clear certain varieties excelled. Saunders Brothers was excited to have found solutions to a potentially devastating disease. They felt they needed to share these genetics with the industry. This sparked the creation of NewGen™ Boxwood.

NewGen™ aims to be the standard bearer of a distinctively better family of boxwood. This new generation of plants promises better tolerance of Boxwood Blight, better resistance to Boxwood Leafminer, and a WOW factor in the landscape.

“To meet the threat of rising pest and disease pressures, as well as maintain boxwood as the foundation of the landscape, we felt we needed a new approach,” says Bennett Saunders, General Manager of Saunders Genetics. “We’ve focused our attention on new and improved genetics, more thorough testing methods and protocols, partnering with like-minded growers, and establishing a distinguished brand identity. We believe NewGen™ represents the future of boxwood for the industry.”

By maintaining bio-secure testing methods and standards, we hope to continue making introductions of superior plants that maintain brand standards. We aim to establish a regional network of premier licensed growers and propagators to share these plants in landscapes all over the United States. We will dedicate 2019 to introducing the program to the industry and its customers, building production on our two initial selections. Plants are scheduled to be available for sale in the spring of 2020. At this time, we are partnering with 4 growers to distribute the product line: Overdevest Nurseries, NJ; Prides Corner Farms, CT; Saunders Brothers Nursery, VA; and Willoway Nurseries, OH.

NewGen™ Boxwood intends to raise the bar for boxwood to meet the changing dynamics of a new generation of the American garden and gardener.

Pictured is the NewGen™ team, Lindsay Day (left) Marketing Coordinator and Bennett Saunders (right) General Manager of Saunders Genetics.