Boxwood Blight Task Force | Virginia Cooperative Extension | Virginia Tech

Boxwood Blight Task Force | Virginia Cooperative Extension | Virginia Tech
Boxwood Blight Task Force
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 in the Virginia Home Landscape
residential boxwood growers
Best Management Practices for Boxwood Blight for Boxwood Greenery Producers
boxwood greenery producers (i.e. used for holiday greenery) and boxwood tippers
Best Management Practices for Boxwood Blight in Virginia Nurseries
nursery operators
Best Management Practices for Boxwood Blight for Professionally Managed Landscapes and Public and Historic Gardens in Virginia
historic garden managers, professional landscapers
Downloadable Decision Options
Downloadable Expanding on Boxwood Blight Management Decision Guide
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).
* 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
Infected susceptible boxwood will decline and eventually die.
Disease will spread in landscape and locally (e.g. neighborhood, town).
Option 2—Remediation after confirmatory diagnosis of boxwood blight
Remove diseased, susceptible boxwood promptly OR, if American boxwood, consider alternative approach for American* (below).
Remove leaf litter from soil surface (e.g. raking/sweeping, vacuuming, or by using a burn torch/agricultural flamer.
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).
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.
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
. 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).
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.)
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.
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.)
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.
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.
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.)
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:
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).
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.
If replacing susceptible boxwood with boxwood blight tolerant (resistant) cultivars:
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
. 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.
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 (
) Virginia Cooperative Extension fact sheet to avoid species of shrubs commonly afflicted with disease problems in Virginia.
Boxwood Blight FAQs
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
Boxwood Blight Image Gallery
Comparison of Boxwood Blight to other Boxwood Problems
No boxwood cultivars 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”.  Boxwood cultivars susceptible to boxwood blight should be avoided.
The tables below list some boxwood that were shown to be resistant to both boxwood blight and leafminer (Table 1) or very susceptible (Table 2) to the boxwood blight pathogen in research trials. New boxwood blight-resistant cultivars will continue to be released into the marketplace and the list of resistant boxwood in Table 1 is not exhaustive.
Table 1. Cultivars of Boxwood resistant to both boxwood blight and leafminer.
Species
Cultivar
B. harlandii
Richard
B. microphylla
Cole’s Dwarf (or Little Missy)
B. microphylla
Golden Dream
B. microphylla
NewGen® Independence
B. microphylla var. japonica
Jim Stauffer
B. microphylla var. japonica
Winter Gem
B. sinica
NewGen®  Freedom
B. sinica var. insularis
Franklin’s Gem
B. sinica var. insularis
Nana
B. sinica var. insularis
Wee Willie
B. sinica var. insularis
Wintergreen
Buxus
Cranberry Creek
Table 2. Some Cultivars Very Susceptible to Boxwood Blight
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
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 ingredient
Example of brand name
Concentration
Contact time/application
Ethanol in spray or liquid form
Lysol disinfectant aerosol spray (Brand III)
70% Ethanol or greater or Lysol Disinfectant Spray Brand III with 58% ethanol and 0.1% dimethyl benzyl ammonium saccharinate
For 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 brands
Prepare 1:9 solution of 5.25% bleach or 1:14 solution of 8.25% bleach. Must be prepared fresh
10-15 min. for equipment surfaces; dip tools for 5 min
Hydrogen dioxide
Oxidate, 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 acid
Xeroton 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 Disinfectant
Prepare 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
Efficacy
FRAC group
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)
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
FRAC group
Propiconazole
Banner MAXX, Procon-Z
F-G
Tebuconazole
Torque
Propiconazole + chlorothalonil
Concert, Concert II
3+M5
Trifloxystrobin + triadimefon
Strike Plus 50 WDG
G-E
3+11
Myclobutanil
Eagle WSP, Rally 40WSP
F-G
Myclobutanil
Myclo-
butanil 20EW T&O
F-G
Thiophanate methyl
Cleary 3336 F, Fungo Flo
Azoxystrobin
Heritage
11
Pyraclostrobin
Insignia
11
Trifloxystrobin
Compass
11
Fludioxonil
Medallion
G-E
12
Mancozeb
Fore 80 WP Rainshield, Protect DF
M3
Chlorothalonil
Daconil Weather Stik Flowable Fungicide
M5
Chlorothalonil + thiophanate methyl
Spectro 90WDG
1+M5
Boscalid + pyraclostrobin
Pageant
7+11
Cyprodinil + fludioxonil
Palladium
F-E
9+12
F=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.
FRAC 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
El tizón de boxwood en viveros de producción comercial
Title
Date
Boxwood Blight Cleanliness Program, Virginia Department of Agriculture and Consumer Services
Boxwood Blight Management
, Department of Plant Pathology, North Carolina State University
Local Virginia Cooperative Extension Offices
Plant Disease Clinic Disease Alerts
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
Devin Bily
State Plant Pathologist
Office of Plant Industry Services, Virginia Department of Agriculture and Consumer Services
David Gianino
State Plant Regulatory Official
VDACS
Mary Ann Hansen
Extension Plant Pathologist Emerita
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
T. Mike Likins
County Agent
Chesterfield County Extension
Lina Rodriguez Salamanca
Plant Disease Clinic Manager
School of Plant and Environmental Sciences, Virginia Tech
Language Translator
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Selecting Landscape Plants: Boxwood
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