Boxwood Blight Task Force

Boxwood Blight

The Virginia Boxwood Blight Task Force provides leadership in safeguarding and protecting the ornamental horticulture industry, historical gardens, and landscape plantings from boxwood blight.

The following BMPs are guidelines for boxwood growers to avoid introduction of the boxwood blight pathogen or, if the disease is already present, to manage the disease in the most effective manner and avoid spread of the disease to new locations. Each BMP is specialized for individual boxwood growing situations.

Best Management Practice Situation
Best Management Practices for Boxwood Blight for Virginia Landscapes, Public Grounds and Historic Gardens professional landscapers, public grounds and historic garden situations
Best Management Practices for Boxwood Blight in the Virginia Home Landscape residential boxwood growers
Best Management Practices for Boxwood Blight in Virginia Production Nurseries WITHOUT Boxwood Blight commercial nursery production
Best Management Practices for Boxwood Blight in Virginia Production Nurseries WITH Boxwood Blight commercial nursery production
Best Management Practices for Virginia Retail Nurseries WITHOUT Boxwood Blight retail garden stores
Best Management Practices for Virginia Retail Nurseries WITH Boxwood Blight retail garden stores
Best Management Practices for Boxwood Blight for Boxwood Greenery Producers boxwood greenery producers (i.e. used for holiday greenery) and boxwood tippers

This decision guide is a general starting place for anyone who has landscape boxwood that have been diagnosed with Boxwood Blight. For
further details to guide your management decision we recommend 1) reading the "Expanding on the Boxwood Blight Management Decision
Guide" and 2) reviewing additional information on the Virginia Boxwood Blight Task Force website (https://ext.vt.edu/agriculture/commercialhorticulture/
boxwood-blight.html).

picture of decision options

* This alternative approach was proposed in response to reports of growers who rejected the option of removal of very large
American boxwood. However, there is not enough research at this time to know how efficacious this approach will be over time in
Virginia and this approach poses risks. It is important to keep in mind that although visibly diseased branches may be pruned out,
pruning out affected branches will not eliminate the Boxwood Blight fungus from American boxwood. Further sporulation of the
fungus on the American boxwood is likely and these spores can serve as a source of inoculum for uninfected boxwood in the
landscape. Also note that weather conditions in Virginia are generally favorable for development of Boxwood Blight and repeated
fungicide sprays may be necessary for much of the year on a 7-day to 2-week schedule, depending on product label directions and
weather conditions. Additionally, it can be difficult to keep up with the sprays required, particularly under prolonged rainy weather.
English boxwood (Buxus sempervirens 'Suffruticosa') is extremely susceptible to Boxwood Blight; therefore, no one is suggesting
using this approach on infected English boxwood.

 

Expanding on the Boxwood Blight Management Decision Guide

Boxwood blight is a serious and contagious boxwood disease.  Management decisions will influence the disease progression.  Although boxwood blight is serious and spreading in many communities in Virginia, boxwood remains a valuable landscape ornamental. Successful and sustainable landscaping with boxwood currently requires knowledge, attention and care.

 

Option 1—Do nothing

  1. Infected susceptible boxwood will decline and eventually die.
  2. Disease will spread in landscape and locally (e.g. neighborhood, town).

 

Option 2—Remediation after confirmatory diagnosis of boxwood blight

  1. Remove diseased, susceptible boxwood promptly OR, if American boxwood, consider alternative approach for American* (below).
  2. Remove leaf litter from soil surface (e.g. raking/sweeping, vacuuming, or by using a burn torch/agricultural flamer.
    1. Diseased boxwood, leaf debris and soil should be double-bagged and removed to the sanitary landfill OR buried 2' deep in soil OR burned (if allowed in your locality).
    2. Do not compost boxwood debris or plant material and do not place curbside for brush pickup, since this will spread the disease to new locations via wind-blown leaves and/or municipal mulch.
    3. Because the fungal spores can stick to tools, equipment, etc., sanitize all tools, equipment, tarps, shoes, gloves, etc., used after removing plants to prevent spread of fungal inoculum to healthy boxwood. For a list of sanitizer recommendations, refer to the Boxwood Blight Task Force website at https://ext.vt.edu/agriculture/commercial-horticulture/boxwood-blight.html. It is recommended that vehicles that have been potentially exposed to the boxwood blight fungus be thoroughly washed of debris (e.g. cleaned at an auto spa).
  3. Mulch soil surface under existing boxwood and/or replacement boxwood to a depth of approximately 2”. (In research studies, a 2”- to 4”-inch mulch layer effectively prevented splash dispersal of boxwood blight spores to lower leaves, but a shallow mulch layer is a better cultural choice for boxwood.)
  4. If leaf debris has been incorporated into the soil, removing soil to a depth of 8" to 12" may help eliminate inoculum of the pathogen, but this is often impractical.
  5. Apply preventative fungicides, as recommended on the product label, to the infected and non-infected boxwood in the vicinity whenever weather conditions are favorable for disease development. (Note that weather conditions in Virginia are favorable much of the year.)
    1. Products containing the active ingredient, chlorothalonil, and labeled for use on landscape ornamentals, have been shown effective when used preventatively (before the disease is present) on boxwood. Professional landscapers have additional active ingredient options. Refer to the fungicide information on the Virginia Boxwood Blight Task Force website for more fungicide information.
    2. Favorable weather conditions for development of boxwood blight: Applications should be made in spring when daytime temperatures reach 60F and prolonged rain is predicted. You can stop spraying when daytime temperatures are regularly above 80F in the summer. Begin sprays again in the fall when temperatures drop below 80F and prolonged rain is predicted. In winter when temperatures regularly stay below 60F you do not need to spray, but pay attention to forecasts for prolonged periods of mild winter weather and rainfall when fungicides might need to be in place.
  6. Monitor other boxwood, pachysandra, and sweetbox in the landscape for development of boxwood blight symptoms. (Other plants in the boxwood plant family, Buxaceae, including Pachysandra spp. and Sarcococca spp., are also susceptible to the disease and should be monitored for boxwood blight. Since they can harbor inoculum for new infections on susceptible boxwood, they should be removed if susceptible boxwood are also in the landscape.)
  7. For recommendations on replacement shrubbery and/or boxwood refer to information in “Option 3” below.

 

*Alternative approach for American boxwood (Buxus sempervirens): Currently some researchers are suggesting that while American boxwood is very susceptible to the Boxwood Blight fungus, it may recover (i.e. produce healthy new growth) during dry weather conditions. Additionally, there have been reports of reluctance of home growers and/or landscape professionals to remove very large American boxwood. For this reason, we have provided an alternative approach for infected American boxwood:

  1.  Prune and remove diseased branches on American boxwood.

                                         i.    Because the fungal spores can stick to tools, equipment, etc., sanitize all tools, equipment, tarps, shoes, gloves, etc., used after removing plants to prevent spread of fungal inoculum to healthy boxwood.

                                        ii.    Follow Steps 2 through 6 (above).

  1.  Precautionary note: This approach may be an acceptable alternative to complete removal of infected American boxwood. However, there is not enough research at this time to know how efficacious this approach will be over time in Virginia. Also, keep in mind that although visibly diseased branches may be pruned out, pruning out affected branches will not eliminate the fungus from American boxwood. Further sporulation of the fungus on the American boxwood is likely and these spores can serve as a source of inoculum for healthy, susceptible boxwood in the landscape and neighborhood landscapes. Also note that weather conditions in Virginia are generally favorable for development of boxwood blight and repeated fungicide sprays will be necessary for much of the year on a 7-day to 2-week schedule, depending on product label directions and weather conditions. English boxwood (Buxus sempervirens 'Suffruticosa') is extremely susceptible to Boxwood Blight; therefore, no one is suggesting that this approach be used on infected English boxwood.

 

Option 3—Replace susceptible boxwood with tolerant (resistant) boxwood cultivars and/or shrub species not susceptible to boxwood blight (Currently there are no boxwood immune to boxwood blight; however, there are boxwood cultivars that are “tolerant” (also termed “resistant”) to boxwood blight. The boxwood blight pathogen may sporulate on tolerant cultivars, but tolerant cultivars do not develop noticeable symptoms of the disease and are not negatively affected by boxwood blight.

 

  1. If replacing susceptible boxwood with boxwood blight tolerant (resistant) cultivars:
    1. It is advisable to purchase replacement boxwood from nurseries that participate in the Boxwood Blight Cleanliness Program (BBCP). A list of participating BBCP nurseries is available at http://www.vdacs.virginia.gov/plant-industry-services-boxwood-blight.shtml . Home growers who want to buy boxwood produced by nurseries in the BBCP will have to do some work to identify a retail store/nursery that sells such boxwood. It is advisable to identify a retail operation that exclusively sells only boxwood produced in the BBCP to minimize the chance of introducing the disease into a landscape.
  2. Only plants in the Buxaceae family (e.g. boxwood [Buxus spp.], pachysandra [Pachysandra spp.] and sweetbox [Sarcoccca spp.] have been reported susceptible to boxwood blight in the landscape. If you are considering replacing susceptible boxwood with other shrub species, refer to the Problem-free Shrubs for Virginia Landscapes (http://pubs.ext.vt.edu/450/450-236/450-236.html) Virginia Cooperative Extension fact sheet to avoid species of shrubs commonly afflicted with disease problems in Virginia.
 

Webinar Title and Presenter

Date      

 Boxwood Blight and Rose Rosette Disease
Webinar presented by Dr. Chuan Hong   
11/16/2017
Boxwood Blight
VCE Master Gardener webinar presented by Mary Ann Hansen
2/3/2017
Boxwood Blight Video Series
VCE Master Gardeners
Various
   

Videos

Date

Boxwood Blight

Chesterfield Now, Chesterfield County, Virginia (Mike Likens, Director Chesterfield County Extension)

2/3/2017

American Boxwood Society Video Library

Various

Various

Downloadable Resistant / Susceptible Boxwood

No boxwood are currently immune to boxwood blight (immune=unable to be infected by the boxwood pathogen). However, there are boxwood cultivars that show only very few minor or barely noticeable symptoms of the disease, despite being infected with the boxwood blight fungus. Such cultivars are characterized as boxwood blight “resistant” or “tolerant”.  Among such cultivars, there are various levels of “resistance” (or “tolerance”) to boxwood blight. For example, a cultivar may be characterized as “very resistant” or “moderately resistant” to boxwood blight. Susceptible cultivars are similarly characterized by their degrees of susceptibility (e.g. “highly susceptible”, “moderately susceptible”, etc.).

The tables below list some boxwood that were shown to be resistant (Table 1) or very susceptible (Table 2) to the boxwood blight pathogen in research trials. Research into boxwood blight resistance is ongoing, so new resistant cultivars will continue to be released into the marketplace.

Table 1. Some Boxwood Blight-Resistant/Tolerant Cultivars1

Species

Cultivar

Leafminer resistance 2

Buxus microphylla var. japonica

Green Beauty

-

B. microphylla

Northern Emerald

-

B. microphylla

Wedding Ring

unknown

B. microphylla

Wintergreen

+

B. microphylla

Golden Dream

++

B. microphylla

Winter Gem

++

B. sinica var. insularis

Nana

++

B. sinica var. insularis

Franklin’s Gem

++

B. sinica var. insularis

Wee Willie

++

B. harlandii

Richard

++

 

Table 2. Some Cultivars Very Susceptible to Boxwood Blight1

Species

Cultivar

Buxus sempervirens

Suffruticosa

B. mycropphylla var. japonica

Morris Midget

B. sempervirens

Justin Brouwers

B. sempervirens

American

B. sempervirens

Halifax American

B. sempervirens

Fineline

B. sempervirens

Black American

B. sempervirens

Arborescens

B. sempervirens

Aurea Pendula

B. sempervirens

Latifolia Maculata

 

1Selected from Ganci, M. L (2014) Investigation of host resistance in Buxus species to the fungal plant pathogen Calonectria pseudonaviculata (=Cylindrocladium buxicola), the causal agent of boxwood blight and determination of overwinter pathogen survival, Master of Science Thesis, North Carolina State University

2 Leafminer resistance rating: ++, very resistant; +, somewhat resistant; -, somewhat susceptible, based on Boxwood Guide, Saunders Brothers, 5th edition (2017)

 

 

 

Downloadable Other Hosts

 

Only plants in the Buxaceae family (e.g. boxwood [Buxus spp.], pachysandra [Pachysandra spp.] and sweetbox [Sarcoccca spp.] have been reported susceptible to boxwood blight in the landscape. Refer to Tables 1 and 2 for a list of species of pachysandra and sweet box reported in the literature as susceptible to boxwood blight.

Table 1. Pachysandra species and cultivars known to be susceptible to the boxwood blight pathogen

Species (common name)

Cultivar

Reference

Pachysandra axillaris (fragrant pachysandra)

Windcliff

(3)

Pachysandra procumbens (Allegheny spurge)

 

(3)

Pachysandra terminalis (Japanese spurge)

Common

(2-4)

 

Crinkled

(3)

 

Green Carpet

(3)

 

Green Sheen

(3)

 

Variegated

(3)

 

1.     Kong P, Likins TM, Hong CX. 2017. First report of Pachysandra terminalis leaf spot caused by Calonectria pseudonaviculata in Virginia. Plant Disease 101:509

2.     LaMondia JA. 2017. Pachysandra species and cultivar susceptibility to the boxwood blight pathogen, Calonectria pseudonaviculata. Plant Health Progress doi:10.1094/PHP-01-17-0005-RS

3.     LaMondia JA, Li DW, Marra RE, Douglas SM. 2012. First report of Cylindrocladium pseudonaviculatum causing leaf spot of Pachysandra terminalis. Plant Disease 96:1069

 

Table 2. Sarcococca (sweet box) species known to be susceptible to the boxwood blight pathogen

Species

Reference

Sarcococca confusa

(6)

Sarcococca hookeriana var. humilis

(1; 5; 6)

Sarcococca orientalis

(6)

Sarcococca ruscifolia

(6)

Sarcococca saligna

(6)

Sarcococca vegans (syn: Sarcococca balansae, Sarcococca vanas)

(6)

Sarcococca wallichii

(6)

 

1.             Kong P, Likins TM, Hong CX. 2017. First report of blight of Sarcococca hookeriana var. humilis by Calonectria pseudonaviculata in Virginia. Plant Disease 101:247

2.             Kong P, Likins TM, Hong CX. 2017. First report of Pachysandra terminalis leaf spot caused by Calonectria pseudonaviculata in Virginia. Plant Disease 101:509

3.             LaMondia JA. 2017. Pachysandra species and cultivar susceptibility to the boxwood blight pathogen, Calonectria pseudonaviculata. Plant Health Progress doi:10.1094/PHP-01-17-0005-RS

4.             LaMondia JA, Li DW, Marra RE, Douglas SM. 2012. First report of Cylindrocladium pseudonaviculatum causing leaf spot of Pachysandra terminalis. Plant Disease 96:1069

5.             Malapi-Wight M, Salgado-Salazar C, Demers JE, Clement DL, Rane KK, Crouch JA. 2016. Sarcococca blight: use of whole-genome sequencing for fungal plant disease diagnosis. Plant Disease 100:1093-100

6.             Ryan C, Williams-Woodward J, Zhang DL. 2018. Susceptibility of Sarcococca taxa to boxwood blight by Calonectria pseudonaviculata. Proceedings of Southern Nursery Association Research Conference 62:64-7

 

 

Sanitizer recommendations for the boxwood blight pathogen

Note: Only ethanol products provide some control of microsclerotia and other pathogen structures (e.g. mycelium, spores, chlamydospores) in plant debris; thus, it is VERY important to wash off surface soil and/or debris before proceeding with any recommended sanitizing procedure.

Active ingredientExample of brand nameConcentrationContact time/application
Ethanol in spray or liquid formLysol disinfectant aerosol spray (Brand III)70% Ethanol or greater or Lysol Disinfectant Spray Brand III with 58% ethanol and 0.1% dimethyl benzyl ammonium saccharinateFor spray applications: Apply to surface and allow to air-dry. For liquid application dip tools for 5 min
Sodium hypochlorite (5.25% or 8.25)Clorox and other household brandsPrepare 1:9 solution of 5.25% bleach or 1:14 solution of 8.25% bleach. Must be prepared fresh10-15 min. for equipment surfaces; dip tools for 5 min
Hydrogen dioxideOxidate, Zerotol
  • Prepare 1:100 – 1:300 solution for use on clean, non-porous surfaces.
  • Prepare 1:50 solution for use on unclean surfaces.
5-10 min
Hydrogen peroxide, peroxyacetic acid, and octanic acidXeroton 3 (X3)
  • Prepare 1:500 – 1:1,500 solution for use on clean, non-porous surfaces.
  • Prepare 1:150 solution for use on unclean, non-porous surfaces.
  • Prepare 1:300 – 1:1,000 solution for use on tools.
10 min
Phenolic compounds (O-benzyl-p-chlorophenol)Lysol Brand Concentrate DisinfectantPrepare solution of 1.25 – 2.5 oz/gal.At least 5 min

Data compiled from: (1) Douglas, S.M., 2013.  Efficacy of sanitizing agents to refine best management practices for the boxwood blight pathogen Calonectria pseudonavicula. APS poster, Annual meeting , Aug. 10-14, Austin TX, (2) Shishkoff, N., 2014. Survival of microsclerotia of Calonectria pseudonaviculata (the boxwood blight pathogen) treated with a variety of sterilants. APS poster, Potomac Division Meeting, March 12–14, Annapolis, Maryland, (3) Dart, N. L., Hong, C. X., Allen, C., 2014.  Efficacy of bleach and ethanol as sanitizers on conidia and infected leaf tissue colonized with mycelium and microsclerotia of the boxwood blight pathogen, Calonectria pseudonaviculata. Unpublished.

Version 1, published December 2014

Downloadable Fungicide Guide

Table 1. Fungicides for boxwood blight management, home grower use.
Active ingredient Trade name Efficacy1 FRAC group2
Chlorothalonil 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 Diseease B Gon (Scotts) E M5
Table 2. Fungicides for boxwood blight management, professional use
Nursery Green-
house
Land-
scape,
non-resid-
ential
Land-
scape, resid-
ential
Active ingredient Trade name Effi-
cacy
1
FRAC group2
  Propiconazole Banner MAXX, Procon-Z F-G 3
  Tebuconazole Torque G 3
  Propiconazole + chlorothalonil Concert, Concert II E 3+M5
    Trifloxystrobin + triadimefon  Strike Plus 50 WDG G-E 3+11
    Myclobutanil Eagle WSP, Rally 40WSP F-G 3
Myclobutanil Myclo-
butanil 20EW T&O
F-G 3
Thiophanate methyl Cleary 3336 F, Fungo Flo  F 1
Azoxystrobin Heritage F 11
Pyraclostrobin Insignia G 11
Trifloxystrobin Compass G 11
Fludioxonil Medallion G-E 12
Mancozeb Fore 80 WP Rainshield, Protect DF G M3
Chlorothalonil Daconil Weather Stik Flowable Fungicide E M5
Chlorothalonil + thiophanate methyl Spectro 90WDG E 1+M5
Boscalid + pyraclostrobin Pageant G 7+11
  Cyprodinil + fludioxonil Palladium F-E 9+12

1F=Fair, G=Good, E=Excellent

  • Effectiveness ratings are based on limited research.  Results can vary depending on environmental conditions, formulation of a pesticide, and application method and timing. These ratings are intended as general guides only.
  • Sources of efficacy information: Gehesquière B. (2014). Phd Thesis. Ghent University, Belgium; Ivors, et al. 2013. Plant Dis. Manag. Rep. 7:OT014. doi: 10.1094/PDMR07; LaMondia, J.A. 2015. Plant Dis. 99: in press; Henricot B. and Wedgwood E. 2013. Plant Health Progress. doi:10.1094/PHP-2013-1024-01-RS; and unpublished research.

2FRAC Group: classification based on fungicide mode of action (www.frac.info). Rotate any fungicide at risk of resistance development with products that have a different mode of action (i.e., in a different FRAC group).

It is the user’s responsibility to read and follow product label directions for all products. Commercial products are named in this publication for informational purposes only. Virginia Cooperative Extension does not endorse these products and does not intend discrimination against other products which also may be suitable. 

Published 2/26/15

Title Date
   
Member Title Affiliation
Anton Baudoin Associate Professor of Plant Pathology School of Plant and Environmental Sciences, Virginia Tech
Adria Bordas Extension Agent Virginia Cooperative Extension, Fairfax County
Elizabeth Bush Extension Plant Pathologist School of Plant and Environmental Sciences, Virginia Tech
Norm Dart State Plant Pathologist Office of Plant Industry Services, Virginia Department of Agriculture and Consumer Services
Mary Ann Hansen Extension Plant Pathologist School of Plant and Environmental Sciences, Virginia Tech
Chuan Hong
Professor and Extension Specialist of Plant Pathology Hampton Roads Agricultural Research and Extension Center, Virginia Tech
Ping Kong Research Scientist Hampton Roads Agricultural Research and Extension Center, Virginia Tech
T. Mike Likins County Agent Chesterfield County Extension
Tina MacIntyre State Cooperative Agricultural Pest Survey Coordinator Office of Plant Industry Services, Virginia Department of Agriculture and Consumer Service
David Gianino State Plant Regulatory Official VDACS