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Best Management Practices forBoxwood Blight in the VirginiaHome LandscapeThis Best Management Practice document is a set of guidelines for homegrowers of landscape boxwood to avoid introduction of the boxwood blightpathogen into a landscape or, if the disease is already present in a landscape,to manage the disease in the most effective manner and avoid spread of thedisease to new locations.What is Boxwood Blight?Elizabeth Bush, Extension Plant Pathologist,Department of Plant Pathology, Physiology andWeed Science, Virginia TechMary Ann Hansen, Extension Plant Pathologist,Department of Plant Pathology, Physiology andWeed Science, Virginia TechNorm Dart, State Plant Pathologist, Office ofPlant Industry Services, Virginia Department ofAgriculture and Consumer ServicesChuan Hong, Professor and Extension Specialistof Plant Pathology, Hampton Roads AgriculturalResearch and Extension Center, Virginia TechAdria Bordas, Extension Agent, VirginiaCooperative Extension, Fairfax CountyT. Mike Likins, County Agent, ChesterfieldCounty ExtensionVersion 2, September 2016PPWS-29NPwww.ext.vt.eduProduced by Communications and Marketing, College ofAgriculture and Life Sciences, Virginia Tech, 2016Virginia Cooperative Extension programs and employment are open to all, regardlessof age, color, disability, gender, gender identity, gender expression, national origin,political affiliation, race, religion, sexual orientation, genetic information, veteran status,or any other basis protected by law. An equal opportunity/affirmative action employer.Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Instituteand State University, Virginia State University, and the U.S. Department of Agriculturecooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech,Blacksburg; M. Ray McKinnie, Interim Administrator, 1890 Extension Program, VirginiaState University, Petersburg.VT/0916/PPWS-85NPBoxwood blight (also known as box blight), caused by the fungus Calonectria pseudonaviculata1, is a serious fungal disease of boxwood that results indefoliation and decline of susceptible boxwood. In Virginia boxwood blightwas first identified in a nursery location in Carroll County in 2011. By thefall of 2013 it was found in other commercial nursery/retail operations andlandscapes in several counties in Virginia. Once introduced to a landscape,boxwood blight is very difficult and costly to control with fungicides. Themajor means of spread of this disease is by movement of contaminated plantmaterial (e.g. container or field-grown boxwood, boxwood greenery usedfor holiday decoration), but boxwood blight spores can also be spread onpruning tools, clothing, equipment and anything that might have contactedinfected plants. Home growers can best protect their boxwood by following the measures listed below to avoid introduction of the disease to theirlandscape.Symptoms of Boxwood BlightThe most characteristic symptoms of boxwood blight on susceptibleboxwood cultivars arebrown leaf spots (Fig. 1)that lead to defoliation(Fig. 2 on page 2) andblack streaking on boxwood stem tissue (Fig. 3on page 3). Some cultivarsof boxwood can harbor theboxwood blight pathogen,yet show no symptoms;these cultivars are considered partially resistant2(also referred to as “tolerant”) cultivars (Table 1 onpage 2). Fungicides canalso mask symptoms of Fig. 1. Leaf spots are typically circular and brownthe disease on susceptible and develop a dark brown border (photo by M.A.Hansen).cultivars.1Synonyms: Cylindrocladium pseudonaviculatum, Cylindrocladium buxicola2Currently there are no boxwood cultivars available that are immune to boxwood blight; however,cultivars possessing various levels of resistance to the disease have been identified and researchis ongoing to rank cultivars according to their level of resistance or susceptibility.
Other plant hostsPachysandra terminalis (Japanese spurge), Pachysandra procumbens (Allegheny spurge) and Sarcococca species (sweetbox), which are in the samefamily (Buxaceae) as boxwood, are also susceptibleto boxwood blight and infected plants of these speciescould introduce the disease to a landscape. Symptomsof the disease on P. terminalis are brown leaf spots.New host plants may be identified as researcherslearn more about this disease, but hosts will likely belimited to members of the Buxaceae family.Avoiding introduction ofboxwood blight to a landscapeFig. 2. Defoliation on boxwood in the planter and the matureplants in the foreground (photo by A.Bordas, VirginiaCooperative Extension).Because the boxwood blight pathogen is not welladapted to long-distance spread by long-distance aircurrents, the most likely entry point for the diseasein a home landscape is by accidental introduction ofinfected plant material and/or contaminated tools,equipment or other items. Home growers who haveboxwood in the landscape should carefully adhereto the following recommendations to avoid inadvertent introduction of this devastating disease to theirlandscape:Table. 1. Susceptibility of 23 commercialboxwood cultivars to boxwood blight(Compiled from research by Ganci, Benson and Ivors,North Carolina State University, 2012. Refer to latestcultivar trial results s/)HighlysusceptibleB. sempervirens ‘Suffruticosa’B. sinica var. insularis ‘Justin Brouwers’Susceptible B. microphylla var. japonica ‘Morris Dwarf’B. microphylla var. japonica ‘Morris Midget’B. sempervirens ‘Jensen’B. sempervirens ‘Marginata’Buxus X ‘Glencoe’ (Chicagoland Green)B. sempervirens ‘American’B. sempervirens ‘Elegantissima’ModeratelysusceptibleBuxus X ‘Green Mound’Buxus X ‘Conroe’ (Gordo)B. microphylla ‘Green Pillow’B. microphylla ‘Grace Hendrick Phillips’B. microphylla ‘Jim Stauffer’Buxus X ‘Green Mountain’ModeratelyresistantB. microphylla ‘Winter Gem’B. sempervirens ‘Dee Runk’B. sempervirens ‘Fastigiata’Buxus ‘Green Gem’B. microphylla ‘John Baldwin’MostresistantB. microphylla ‘Golden Dream’B. harlandii(recommendedB. sinica var. insularis ‘Nana’for newplantings)B. microphylla var. japonica ‘Green Beauty’Fig. 3. Dark streaks on stems (photo by M.A. Hansen).www.ext.vt.edu2
When purchasing boxwood plants for transplantingto a landscape, ask nursery personnel if theirboxwood are from producers participating in theBoxwood Blight Cleanliness Program. Productionnurseries participating in this program adhere to strictmanagement practices that minimize the chance ofintroduction of this disease to their nurseries and areinspected by the Virginia Department of Agricultureand Consumer Services (VDACS) for the presence ofboxwood blight. A link to information on the BoxwoodBlight Cleanliness Program and other useful links canbe found at the Virginia Boxwood Blight Task Forceweb site al-horticulture/boxwood-blight/).What to do if boxwood blight issuspected in a landscapeVirginia growers should submit suspect plant samplesfor diagnosis to the local Virginia Cooperative Extension (VCE) office (http://www.ext.vt.edu/offices/).VCE can send samples for confirmatory diagnosis tothe Virginia Tech Plant Disease Clinic. Collect symptomatic boxwood samples (stems withblack streaks, leaf spots, or defoliation) and doublebag in sealed plastic bags before transporting to yourExtension office.- Plant samples should be accompanied by acompleted plant diagnostic form (456-097),available at the county Extension office. Prior to purchase, carefully inspect plants forsymptoms of boxwood blight. Confirmatory diagnosis of this disease by a plantdiagnostic lab is important because other problemson boxwood could be mistaken for boxwood blight.Additionally, to reduce spread of this serious disease,it is important for VCE to know where outbreaksof the disease occur and identify the source of anyboxwood blight-diseased plant material.- Be aware that partially resistant cultivars ofboxwood (Table 1) could act as a “Trojan horse”in a landscape because partially resistant cultivarsmay harbor the boxwood blight pathogen, yet notshow obvious symptoms.- Be aware that fungicide treatment can suppresssymptom development.What to do if boxwood blight isdiagnosed in the landscape Monitor established boxwood and newly plantedboxwood on a regular basis for any symptoms ofboxwood blight.Since boxwood blight cannot be effectively controlledonce the infection begins, prompt removal of any diseased boxwood is recommended to help prevent spreadof disease to healthy plants. Associated leaf debrisshould also be removed. Be aware that removing diseased boxwood and leaf debris will not eradicate theboxwood blight pathogen from the location, sincethe pathogen produces long-lived survival structuresthat can persist in the soil for 5 to 6 years. These survival structures can infect susceptible replacement boxwood planted in locations where the disease has beendiagnosed. Therefore, replanting susceptible boxwoodcultivars or members of the Buxaceae family in a location where infected boxwood has been removed is notadvisable. Partially resistant boxwood cultivars (Table1) could be used as replacement plants, but repeatedfungicide applications will be necessary to protect anysusceptible boxwood cultivars that remain in the landscape. Boxwood cultivars with a high level of resistance(termed “most resistant” in Table 1) will not require fungicide treatment. Be aware that boxwood greenery used for holidaydecoration could harbor the boxwood blight pathogen.- To minimize risk of introducing the disease by thisroute, do not use boxwood greenery near landscapeboxwood.- When disposing holiday greenery, double-bag it insealed plastic bags and dispose of it in the landfill.Do not compost boxwood greenery. The boxwood blight fungus can be spread fromone property to another via contaminated sprayhoses, pruning tools, wheelbarrows, tarps, vehicles,clothing, shoes, or anything to which the stickyspores of the boxwood blight fungus might adhere.In fact, boxwood blight was reported to have spreadfrom boxwood in one landscape to another landscapein North Carolina on a spray hose used to applyinsecticides for boxwood leafminer control.www.ext.vt.edu3
After removal of diseased plants and debris, different management approaches should be considered,depending on the particular landscape situation. Thetwo different scenarios outlined below illustrate tworecommended, but different, management approaches:infection and spread, so any time temperaturesare over 60 F and rainfall is expected, apreventative fungicide spray program shouldbe in place.2. Monitor boxwood weekly during the growingseason for symptoms of boxwood blight. Removeany symptomatic plants/debris/soil as outlinedabove.Scenario 1A landscape contains highly valued boxwood that aresusceptible to boxwood blight, symptoms of boxwoodblight were observed in the planting, and the diseasewas confirmed by a plant diagnostic lab (e.g. the VCEPlant Disease Clinic).3. Boxwood debris should never be composted. Bagand dispose of in the landfill OR bury 2’ deep in alocation away from boxwood plantings.4. When working in boxwood plantings, minimizethe chance of spreading boxwood blight inoculumthat could be present on shoes, gloves, clothing,equipment and tools by sanitizing between plants/plantings (Table 3).Immediate Actions Recommended1. Remove diseased boxwood and leaf litter promptly.Remove leaf litter from soil surface by vacuuming,raking, orsweeping. If leaf debris has beenincorporated into the soil, removing soil to a depthof 8” to 12” may help eliminate fungal inoculum ofthe pathogen. Diseased boxwood, leaf debris, andsoil should be bagged and removed to the landfillOR buried 2’ deep in soil away from boxwoodplantings. Do not compost boxwood debris orplant material.5. Implement the suggested cultural practices in thesection below: “Cultural Practices Recommendedto Minimize Chance of Boxwood Blight.”Scenario 2A landscape contains boxwood plants that developedsymptoms of boxwood blight and the disease was confirmed by a plant diagnostic lab (e.g. Plant DiseaseClinic); however, the boxwood in this landscape are nothighly valued specimens. In this situation the simplestapproach would be to replace boxwood blight-susceptible boxwood with boxwood cultivars that possessa high level of resistance (termed “most resistant” inTable 1) purchased from a nursery in the BoxwoodBlight Cleanliness Program (Table 1). This will allowthe grower to enjoy the beauty of boxwood plantingswithout the significant burden of repeated fungicidesprays to susceptible boxwood over the lifetime of theplanting.2. Because the fungal spores can stick to tools,equipment, etc., sanitize all tools, equipment, tarps,shoes, gloves, etc., used after removing plants toprevent spread of fungal inoculum to healthyboxwood (Table 3).3. Promptly begin a preventative fungicide sprayprogram on any susceptible boxwood in thelandscape to prevent further disease outbreaks.4. Be aware that pets, children, and other animalscan also potentially move the sticky spores of thisfungus to new locations.1. All susceptible boxwood should be removed,including the roots. Infested plant debris shouldbe removed by raking, sweeping, or vacuuming,then bagged and taken to the landfill. Alternatively,debris can be buried 2’ deep in soil away fromlandscape plantings. Do not compost diseasedplant material. Be aware that removing diseasedboxwood and leaf debris will not eradicate theboxwood blight fungal pathogen from the location,since the pathogen produces long-lived survivalstructures that can persist in the soil for 5 to 6 years.Long-term Actions Recommended1. Repeat fungicide applications (7- to 14-dayintervals, according to product label) to susceptibleboxwood throughout the growing season for thelife of the boxwood plants.a. If temperatures warm after the growing seasonhas ended, additional fungicide applicationmay be warranted. Warm temperatures plus leafwetness are very favorable for boxwood blightwww.ext.vt.edu4
3. Fungicides labeled for use by home growersare protectant fungicides and must be usedpreventatively.2. If boxwood leaf debris has been incorporated intothe soil, removing soil to a depth of 8” to 12” mayhelp eliminate survival structures of the pathogen.Dispose of soil and leaf litter as recommendedabove for diseased plant material. Do not compost.4. An effective preventative fungicide sprayprogram will require repeated applications (at 7to 14-day intervals, depending on product labeland environmental conditions) of fungicidesthroughout the growing season.3. Sanitize all tools, equipment, tarps, shoes, gloves,clothing, etc., used when removing plants toprevent spread of fungal inoculum that can causeinfection on healthy boxwood (Table 3).5. Post-growing season: Warm temperatures withleaf wetness results in high boxwood blightdisease pressure, so if temperatures are over60 F and a rain event is expected, a preventativefungicide spray should be in place post-season aswell.4. Replant with boxwood cultivars that possess ahigh level of resistance (termed “most resistant”in Table 1) purchased from nursery producers whoare in the Boxwood Blight Cleanliness Program.Fungicide management of boxwoodblight in the home landscape6. Thorough fungicide coverage of boxwood foliageis difficult, yet necessary for protection from thedisease.Important considerations for home growers whendeciding whether to implement a preventative fungicide management program for boxwood in the homelandscape are:Currently, effective fungicide options for home growers are limited; however, professional applicators inthe home landscape have more product options. Futureresearch may lead to development of effective controlof boxwood blight for home growers with fewer fungicide applications. For a list of specific fungicideslabeled for control of boxwood blight in the landscapefor use by non-professional applicators, refer to Table2.1. Fungicides cannot eradicate the disease frominfected plants.2. Once boxwood blight is present in the landscape, itis very difficult to control. Fungicide applicationsthat are begun after the disease is already present donot provide acceptable disease control, accordingto the latest research results from North CarolinaState University.Cultural Practices Recommended toMinimize Chance of Boxwood Blight Purchase boxwood from nursery producers in theBoxwood Blight Cleanliness Program.Table 2. Products containing the active ingredient chlorothalonil have been shown to be veryeffective in management of the boxwood blight pathogen, if used preventatively.Active ingredientBrand name and manufacturerchlorothalonil- Broad Spectrum Landscape & Garden Fungicide (Ferti-lome)- Vegetable, Flower, Fruit and Ornamental Fungicide (Hi-Yield)- Fung-onil (Bonide)- Ortho Max Garden Disease Control or Ortho Disease B Gon (Scotts)Note: Read and follow label directions for all products. Commercial products are named in this publication for informational purposes only. The authors do not endorse these products and do not intend discrimination againstother products that also may be suitable.www.ext.vt.edu5
Minimize leaf wetness and promote good aircirculation in boxwood plantings to minimize diseasepressure. Examples include:of introduction of boxwood blight if the tippersvisit multiple boxwood plantings and do not followgood sanitation practices.- Choose cultivars that have a more open-growthhabit (e.g. Buxus microphylla cultivars as opposedto B. sempervirens ‘Suffruticosa’).- If you hire landscape professionals to spray orotherwise maintain landscape boxwood, discussyour concern about boxwood blight with them tolearn about management practices they may havein place to avoid movement of boxwood blightfrom one client’s landscape to another. Then youcan decide if their approach is acceptable to you.- Avoid overhead irrigation.- Ensure good air circulation in plantings byproviding adequate spacing between plants. Ingeneral, growers may want to avoid close spacingof boxwood and, therefore, hedges.RecordkeepingKeep accurate records of boxwood cultivar namesand locations on your property and where and whenplants were purchased (or otherwise obtained). Keeprecords on location(s) of any diseased boxwood thatare removed. Keep records of fungicide applications,including product information and date of application. Mulch boxwood plantings to reduce the spread ofboxwood blight inoculum to foliage by splashingwater. Avoid working in boxwood plantings when thefoliage is wet and fungal inoculum is more likely tobe spread.New Landscape Plantings Practice good sanitation practices to avoid movinginfested soil or plant material to landscape locationswhere boxwood are located.Purchase boxwood from nursery producers in the Boxwood Blight Cleanliness Program. When consideringnew boxwood plantings in the home landscape, consider installing boxwood blight cultivars that possessa high level of resistance (termed “most resistant” inTable 1), which have the glossy green, evergreen foliage and growth habits valued by many Virginia homegardeners. The boxwood blight pathogen can live andproduce spores on these partially resistant cultivars,but cultivars with a high level of resistance, even ifinfected, will thrive and do not show noticeable symptoms of the disease.- Sanitize pruning tools and other tools/equipment/clothing/tarps between boxwood plantings and alsobetween other members of the Buxaceae family.- Bag and dispose of all boxwood debris (includingholiday greenery) in the landfill or bury 2’ deep insoil away from boxwood plantings.- Be aware that allowing boxwood tippers onto yourproperty to collect greenery may increase the riskTable 3. Sanitizers for equipment/tools.Follow label directions and precautions on all labeled products. Surfaces must be free of soil and other organicmatter for sanitizers to be effective. The highest label rate is recommended. For best efficacy, at least 5-minutecontact time with sanitizing agent is recommended for tools; for pots or other surfaces, at least 10 minutes. Theseproducts are corrosive, so oil tools after treatment.Active ingredientBrand Nameso-Benzyl-p-chlorophenol (1.25 oz/gallon)Lysol Concentrate Disinfectantsodium hypochlorite (1 part bleach: 9 parts water)Clorox, other brands of household bleach (must beprepared fresh)Note: Read and follow label directions for all products. Commercial products are named in this publication for informational purposes only. The authors do not endorse these products and do not intenddiscrimination against other products that also may be suitable.www.ext.vt.edu6
2 www.ext.vt.edu Fig. 3. Dark streaks on stems (photo by M.A. Hansen). Other plant hosts Pachysandra terminalis (Japanese spurge), Pach- ysandra procumbens (Allegheny spurge) and Sar- cococca species (sweetbox), which are in the same family (Buxaceae) as boxwood, are also susceptible to boxwood blight and infected plants of these species
