NEW Blight Ravages Boxwoods - Cornell Cooperative Extension of ...

<strong>NEW</strong> <strong>Blight</strong> <strong>Ravages</strong> <strong>Boxwoods</strong><br />

Adapted from Proceedings <strong>of</strong> the 2012 SAF Production and Pest Management Conference<br />

Buxus infected with box blight displaying leaf drop.<br />

Photo by Jadwiga Komorowska-Jedrys<br />

<strong>Extension</strong> Education Center<br />

423 Griffing Avenue, Suite 100<br />

Riverhead, New York 11901-3071<br />

t. 631.727.7850<br />

f. 631.727.7130<br />

suffolk@cornell.edu<br />

www.ccesuffolk.org<br />

There is a new, aggressive, exotic disease<br />

affecting boxwoods on Long Island called<br />

boxwood or box blight, which is caused by the<br />

fungus Cylindrocladium buxicola (synonym C.<br />

pseudonaviculatum). Although this new disease<br />

was active on the east coast during and possibly<br />

before the summer <strong>of</strong> 2011, the pathogen was<br />

only properly identified as present in the country<br />

in October, 2011. Since its initial find in the US,<br />

the disease has been detected in MD, NC, NY, OR,<br />

PA, RI, VA, and CT. In NY, the blight has been<br />

identified in Nassau, Suffolk, Dutchess, and<br />

Westchester counties. It is likely that other areas<br />

where boxwood is grown will soon be discovering<br />

the blight because the pathogen spreads by<br />

shipment <strong>of</strong> diseased plants. Box blight was<br />

observed for the first time causing problems in<br />

the United Kingdom in 1994. Since then, it has<br />

spread to numerous European countries, Canada,<br />

and New Zealand.<br />

Initially, symptoms <strong>of</strong> box blight include round, brown leaf spots or leaf tip lesions, which may be easily<br />

overlooked. The disease quickly progresses to conspicuous leaf drop, and the bare twigs typically show black<br />

cankers. In a diagnostic lab, the leaves and twigs can be examined for the characteristic fruiting <strong>of</strong> the fungus<br />

with the aid <strong>of</strong> a microscope. It is important to distinguish this new Cylindrocladium disease from other<br />

common boxwood problems such as Volutella blight and Macrophoma blight. It is impossible to tell which<br />

disease is affecting boxwood by field observations alone. One indicator is that Volutella blight typically affects<br />

stressed boxwoods, while the new box blight typically affects healthy plants when temperature and moisture<br />

conditions permit.<br />

The boxwood blight pathogen thrives under typical spring and fall weather conditions <strong>of</strong> the northeast, with<br />

temperatures <strong>of</strong> 18-25°C (64-77°F) and high humidity being most favorable. A complete disease cycle (from<br />

infection to sporulation) can take as little as 7 days. The pathogen can also grow below 10°C. However, hot<br />

summer temperatures are not favorable – growth is halted at 30°C and the fungus is killed at 35°C.<br />

All ornamental species <strong>of</strong> boxwoods are susceptible to boxwood blight. (See below for a list <strong>of</strong> hosts that can<br />

be naturally infected.) Other Buxus species have been found to be susceptible when inoculated by<br />

researchers. Although it has not been seen infected in nature, sweetbox (Sarcococca hookeriana) was also<br />

susceptible when inoculated.

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Some Hosts <strong>of</strong> Cylindrocladium buxicola (natural infection observed) 1<br />

Common (American) boxwood:<br />

B. sempervirens<br />

B. sempervirens ‘Angustifolia’<br />

B. sempervirens ‘Arctic Emerald’<br />

B. sempervirens ‘Blauer Heinz’<br />

B. sempervirens ‘Compacta’<br />

B. sempervirens ’Elegantissima’<br />

B. sempervirens ‘Graham Blandy’<br />

B. sempervirens ‘Jade Pillar’<br />

B. sempervirens ‘Latifolia Maculata’<br />

B. sempervirens ‘Memorial’<br />

B. sempervirens ‘Variegata’<br />

English boxwood:<br />

B. sempervirens ‘Suffruticosa’<br />

B. sempervirens ‘Suffruticosa variegata’<br />

Korean boxwood:<br />

B. sinica var. insularis ‘Justin Brouwers’<br />

B. sinica var. insularis ‘Winter Gem’<br />

B. sinica var. insularis ‘Winter Green’<br />

Hybrids:<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Green Mountain’<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Green Gem’<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Green Velvet’<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Chicagoland’<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Green Ice’<br />

B. sinica var. insularis X B. sempervirens hybrid ‘Big Leaf Gordo’<br />

Littleleaf boxwood:<br />

B. microphylla ‘Faulkner’<br />

B. microphylla var. Japonica ‘Morris Midget’<br />

B. microphylla var. japonica ‘National’<br />

B. microphylla var. japonica ‘North Star’<br />

B. microphylla var. japonica ‘Green Beauty’<br />

B. microphylla var. japonica ‘Baby Gem’<br />

1 Sources: Douglas, S. M. 2011. Boxwood blight—a new disease for Connecticut and the U. S.<br />

http://www.ct.gov/caes/lib/caes/documents/publications/fact_sheets/plant_pathology_and_ecology/boxwood_blight-<br />

_a_new_disease_for_connecticut_and_the_u.s.__12-08-11.pdf<br />

Henricot, B. 2006. Box blight rampages onward. The Plantsman 5:153‐157.<br />

<strong>Extension</strong> Education Center<br />

423 Griffing Avenue, Suite 100<br />

Riverhead, New York 11901-3071<br />

t. 631.727.7850<br />

f. 631.727.7130<br />

suffolk@cornell.edu<br />

www.ccesuffolk.org<br />

Box <strong>Blight</strong> can produce leaf spots, leaf drop, and black cankers on<br />

Buxus twigs. Photo by Jadwiga Komorowska-Jedrys<br />

It is difficult to predict the exact impact <strong>of</strong> this new boxwood disease, but European experience makes it clear<br />

that both gardeners and the horticulture industry need to take this disease very seriously in order to prevent it<br />

from becoming a common, established problem everywhere boxwood is grown. <strong>Boxwoods</strong>, highly valued<br />

here on Long Island for their deer resistance and evergreen nature, could easily change from a ubiquitous<br />

landscape ornamental to a rare, unsustainable plant.<br />

Accurate identification followed by prompt action can help slow the spread <strong>of</strong> this serious disease. Any<br />

horticultural business or homeowner with boxwoods currently on their property should search for symptoms

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<strong>Extension</strong> Education Center<br />

423 Griffing Avenue, Suite 100<br />

Riverhead, New York 11901-3071<br />

t. 631.727.7850<br />

f. 631.727.7130<br />

suffolk@cornell.edu<br />

www.ccesuffolk.org<br />

immediately. If you see large areas <strong>of</strong> bare twigs on any species <strong>of</strong> boxwood this winter (in the nursery,<br />

landscape, or garden center), or dramatic leaf spotting, defoliation, and dieback during the growing season,<br />

send in a sample for laboratory identification. Commercial samples should be sent to the LI Horticultural<br />

Research & <strong>Extension</strong> Center at 3059 Sound Ave, Riverhead, NY 11901 / 631‐727‐3595. Non‐commercial,<br />

homeowner samples should be sent to the CCE <strong>of</strong> Suffolk County Diagnostic Lab at 423 Griffing Ave,<br />

Riverhead, NY 11901 / 631‐727‐4126.<br />

If a positive identification <strong>of</strong> boxwood blight is made, diseased plants and all plant debris must be removed as<br />

thoroughly and quickly as possible. Currently, this new species <strong>of</strong> Cylindrocladium will not be able to be<br />

controlled with fungicides. Masking the problem with fungicides rather than taking more strict eradication<br />

actions would be a mistake – the disease will then become extensively distributed. Sanitation efforts after a<br />

disease outbreak must be extremely thorough — after bagging and removing diseased plants, any leaves left<br />

behind must be gathered, removed, and burned or buried. Vacuuming may be a good option for hardscape<br />

and in the nursery. Because the pathogen can survive in fallen leaves for up to 5 years, composting is not an<br />

option. All boxwoods and boxwood leaf debris remaining in a garden center or landscape this winter should<br />

be destroyed if this disease is found, and if new boxwoods are introduced, they should be placed as far as<br />

possible from where boxwoods were set in 2011.<br />

In the future, the horticulture industry will probably find it desirable to produce alternate evergreen<br />

ornamentals. Valuable historic gardens would be wise to not introduce any Buxus plants for the foreseeable<br />

future, in order to avoid introducing this fungus.<br />

For More Information<br />

• Bulletin from Connecticut Agricultural Experiment Station by Sharon Douglashttp://www.ct.gov/caes/lib/caes/documents/publications/fact_sheets/plant_pathology_and_ecology/boxwood_blight-<br />

_a_new_disease_for_connecticut_and_the_u.s.__12-08-11.pdf<br />

• A webinar presented by Kelly Ivors at NC State University on January 5, 2012 is available athttp://go.ncsu.edu/box_blight_webinar<br />

• An excellent North Carolina fact sheet is available by Googling “NC Pest Alert box blight.”<br />

• Henricot, B. 2006. Box blight rampages onwards. The Plantsman 5:153‐157.<br />

This publication was created by Margery Daughtrey, Plant Pathologist, <strong>Cornell</strong> University and<br />

Alexis Alvey, Nursery & Landscape Specialist, <strong>Cornell</strong> <strong>Cooperative</strong> <strong>Extension</strong> <strong>of</strong> Suffolk County<br />

January 2012 (updated February 2012)<br />

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