Issue 9, June 20, 2016
Boxwood Blight Special Screening Service
Boxwood Blight is an exotic fungal disease which can infect members of the Buxaceae family. It has been confirmed on boxwood, pachysandra, and sarcococca. It was first described in the United Kingdom in the mid-1990s. Since then, it has been found throughout Europe and in New Zealand. The pathogen was identified for the first time in the United States in 2011. Boxwood blight has now been found in 19 states: AL, CT, DE, FL, GA, MA, MD, MO, NC, NH, NJ, NY, OH, OR, PA, RI, SC, VA, and WV. To date, this disease has not been found in Illinois.
It is important to note that, just because the pathogen has been found in a state, that does not mean the pathogen has become established. Boxwood blight moves long-distance on infected nursery stock, and some confirmations have been in nurseries where the infected plants have been destroyed before being sold.
There are three characteristic symptoms of boxwood blight: leaf spots, stem cankers, and defoliation. Common fungal diseases such as Volutella Blight and Macrophoma Leaf Spot, damage from insect pests including Boxwood Leafminer, and abiotic issues such as winter damage are often mistaken for Boxwood Blight.
Leaf Spots
Spots start off as light or dark brown circular areas on leaves, usually with a yellow halo. As the spots increase in size, the entire leaf becomes blighted. If the infection starts near the leaf margin, a wedge-shaped lesion may develop. Lesions are usually visible on both sides of the leaf.
Photo credits: left: N. Gregory, University of Delaware; middle: Sabrina Tirpak, Rutgers PDL; right: North Carolina State University Plant Disease and Insect Clinic
Stem Cankers
Dark brown or black, diamond-shaped or linear cankers are clearly defined against green stems.
Photo credits: left: Kelly Ivors, California Polytechnic State University; middle: Kate Aitkenhead, USDA APHIS-PPQ; left: Meg Williamson, Clemson Plant Problem Clinic
Defoliation
This is a classic symptom of boxwood blight as other boxwood problems do not typically cause defoliation.
Photo credits: left: Sabrina Tirpak, Rutgers PDL; middle: Mary Ann Hansen, Virginia Polytechnic Institute and State University; right: Nicole Ward Gauthier, UK
Because boxwood blight has the potential to seriously impact Illinois landscapes and nursery production, the University of Illinois Plant Clinic is offering free screening of suspect samples from Illinois in 2016. There is no charge for these samples, but reports for these samples will not be provided. If you would like a full diagnostic report including management recommendations, please submit it as a general sample.
For a copy of the Plant Clinic Special Report and screening submission form, please see: https://uofi.box.com/s/4hnabgy1i7aftjb08sa66nhc1zcyal0l
If you have questions about this service, or about boxwood blight in general, please contact us at (217) 333-0519 or plantclinic@illinois.edu. (Diane Plewa)
Author:
Diane Plewa