Boxwood Blight, a new disease of boxwood in the U.S. Alan Windham, Professor, Plant Pathology Mark Windham, Professor, Plant Pathology Anni Self, Plant Pathologist, TN Dept of Agriculture

Boxwood Blight, why the concern? Boxwood is an important landscape plant in American gardens and a valuable crop produced by nurseries This fungal disease attacks all commercially available boxwood species and cultivars Boxwood blight can defoliate a boxwood in one season Boxwood cuttings, plants in containers and those established for decades are susceptible Fungicides give moderate to poor control Has been found in 9 states in the U.S. (MA, RI, CT, NY, PA, MD, VA, NC, OR); this number will likely increase

Boxwood Blight Time Line First reported in the United Kingdom in mid-1990’s (now considered widespread throughout Europe) Reported in New Zealand in 2002 Reported in CT and NC in October 2011 By February 2012 reported in MA, MD, VA, RI,OR,NY, PA and British Columbia

The Pathogen Cylindrocladium buxicola (syn C. pseudonaviculatum) L. Lacey & K.Ivors, NCSU

Boxwood Blight Symptoms* Tan-to-brown circular spots on leaves With time whole leaves turn brown and are shed Tan-to-black lesions develop on twigs Root system is not affected, at least initially; as plant declines the root system will be affected * Disease symptoms – visible damage to leaves, stems or other plant parts

Boxwood Blight signs* During humid, wet conditions the fungus may sporulate on the underside of leaves and stems Spore masses are white on infected leaves and stems * Sign – visible signs of the pathogen (masses of spores, mycelium)

Signs and Symptoms of Boxwood Blight Photos courtesy of S. Douglas, CT Ag Exp Station

Boxwood Blight, symptoms on stem Photo courtesy of S. Douglas, CT Ag Exp Station

Boxwood Blight Damage to Cuttings in Propagation Bed

Container Nursery: plants were defoliated in 7-10 days

Boxwood Blight of Boxwood Defoliation of boxwood in one season due to box blight Photos courtesy of M. Inman, CT Ag Exp Station

Boxwood Blight Defoliation of box wood due to box blight infection Photo courtesy of S. Douglas, CT Ag Exp Station

Spread Short distance the fungal spores can be splash dispersed or by wind driven rain Long distance spread via infected plant material Wet foliage and warm, humid conditions favor disease development Fungus can survive for years in leaf litter via micro-sclerotia

Host Cultivar Buxus microphylla var. japonica ‘North Star’ ‘Green Beauty’ ‘Baby Gem’ Buxus sempervirens ‘Suffruticosa’ ‘Elegantissima’ ‘Artic Emerald’ ‘Jade Pillar’ ‘Graham Blandy’ Buxus sinica var. insularis ‘Winter Gem’ ‘Winter Green’ Buxus sinica var. insularis X Buxus ‘Green Mountain’ sempervirens hybrid ‘Green Gem’ ‘Green Velvet’ ‘Chicagoland’ ‘Green Ice’ ‘Big Leaf Gordo’ Hosts for Boxwood Blight in CT All commercially produced boxwood species/cultivars are considered hosts

Best Management Practices for Landscapes Be extremely cautious if buying boxwood this season Examine plants carefully before buying; if not healthy, walk away Fungicides slow, but do not eliminate the disease Isolate new plants from established plantings Contact your local Extension Agent for more information

Best Management Practices for Nurseries Train staff to recognize boxwood blight signs and symptoms Closely inspect incoming boxwood and isolate new plants from older blocks of boxwood Scatter boxwood blocks throughout nursery If possible, use drip irrigation Take cuttings for propagation from healthy plants Keep up-to-date on developments in fungicide trials Contact your plant inspector or Extension agent if you see anything suspicious

Look-a-like Diseases Phytophthora root rot Volutella blight

Phytophthora root Rot Roots are killed; foliage dies once roots are dead Problem in nurseries and newly established plants in landscapes

Phytophthora Root Rot

Phytophthora Root Rot Healthy Phytophthora root rot; note discolored roots

Volutella Blight A minor problem compared to boxwood blight Shoots may be killed Sign of disease- pink-to-salmon colored spores on leaves

Volutella Blight S Douglas, CT Ag Exp Stat P Bachi, Univ of KY, ipmimages.org

Further Reading Boxwood Blight, CT Ag Exp Station Boxwood Blight, NC State University