Boxwood Blight - University of Maryland Extension

Boxwood Blight (or Box Blight)
Integrated Pest Management for Commercial Horticulture
extension.umd.edu/ipm PEST ALERT - 2013
Introduction
A new disease called Box Blight or Boxwood
Blight has been causing defoliation of boxwood
throughout Europe since the late 1990’s. The
disease is caused by a fungus called Cylindrocladium
pseudonaviculatum (synonym: Cylindrocladium
buxicola). In October, 2011, the disease was found
in North Carolina and Connecticut in both nursery,
and landscape plantings. The disease was also
found in a Virginia nursery. Since this first US
report the disease has been identified in a number of
northeastern states and also in Oregon, and British
Columbia. The first Maryland case of Boxwood
Blight was confirmed on plants from a landscaper’s
nursery in December, 2011.
Symptoms
All aboveground portions can be infected. Symptoms
begin as dark or tan leaf spots which coalesce to
brown blotches, often with dark “zone lines” in the
blighted areas. Infected leaves fall from the twigs,
resulting in defoliation that starts on the lower
branches and moves upward in the canopy. A key
symptom that differentiates Boxwood Blight from
other boxwood diseases is the development of
numerous narrow black lesions (cankers) on green
stems. The pathogen does not attack roots, but
repeated defoliation and dieback from stem
Boxwood Blight Symptoms
Boxwood Blight Stem Cankers
cankers has killed small rooted cuttings in nursery
propagation. Infected plants lose ornamental value as
defoliation becomes severe.
Disease Cycle
The pathogen can overwinter in fallen infected
leaves, which can serve as a source of infection for
subsequent years. Cushion-like spore structures of
the fungus are readily produced on infected leaves
and stems during the growing season. Spores from
these structures can be splash-dispersed through
irrigation or rainfall resulting in spread of the disease
within a plant or to nearby boxwood shrubs. The
primary method of long distance disease spread is
movement of infected plants through nursery trade,
use of contaminated tools and transport vehicles that
contain fallen infected leaves.
Boxwood Blight Twig With
Conidiophores

Hosts
American, English and Korean boxwood are all
susceptible to this new disease although some
variation in disease severity among cultivars has been
reported. Sweet box, Sarcococca, an ornamental
that is in the boxwood family (Buxaceae) has been
infected under experimental conditions. In 2012,
the disease was confirmed causing leaf spots with
yellow margins on Japanese pachysandra in a
Connecticut landscape. According to Connecticut
Agriculture Experiment Station plant pathologists,
the pachysandra infections appear to have originated
from adjacent infected boxwood plants. The disease
has not been reported on pachysandra in nurseries or
garden centers.
Management
Sanitation is critical for management of Boxwood
Blight. Diseased plants should be removed, bagged
and disposed in municipal waste or buried under at
least 2 feet of soil. Where permitted, infected plants
may be burned. Plant debris should be collected by
vacuuming, sweeping or raking, and then bagged and
disposed in municipal waste. Infected plants or plant
debris should not be composted.
Research is under way to test the effectiveness of
fungicides for management of Boxwood Blight in the
United States.
An accurate diagnosis is very important in managing
this disease. If you suspect you see boxwood infected
with Boxwood Blight, please send samples of
twigs and foliage (wrapped in dry paper towels and
Boxwood Blight
enclosed in double Ziploc bags) to the University
of Maryland Plant Diagnostic Laboratory for
diagnosis. Submission information can be found at
the University of Maryland Diagnostic Laboratory
website at www.plantclinic.umd.edu.
by
Karen K. Rane, Director of the UMD Plant Diagnostic Clinic,
University of Maryland Extension, College Park, MD, rane@umd.edu
David L. Clement, Extension Specialist in Plant Pathology,
University of Maryland Extension, clement@umd.edu
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January 2013