Volutella Blight Causing Boxwood Dieback.

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Landscapers and gardeners may be seeing scattered dieback on boxwoods this spring.  One candidate for the sectional dieback is Volutella blight.  Both English and American boxwoods are susceptible to this disease which is caused by the fungal pathogen, Pseudonectria buxi (also called Volutella buxi). 

Sectional Foliar Discoloration from Volutella Canker
Sectional Foliar Discoloration from Volutella Canker on Boxwoods

The fungus targets stems where it produces girdling infections.  Symptoms first appear in the spring and intensify with new growth.  Leaves turn light yellow then brown and eventually drop from infected stems.  A close examination of the affected stems may reveal loose bark and constricting girdling.  A careful removal of the bark will expose chocolate colored phloem tissue with a distinct transition zone between dead stem tissue and healthy green tissue.  The disease may be managed by pruning a few inches beneath the transition zone.  Of course, sanitation pruning may significantly disfigure heavily infected plants.

Sectional Dieback from Volutella Canker on Boxwoods
Sectional Dieback from Volutella Canker

NOTE:  boxwood defoliation and dieback may also be caused by a number of other problems including salt damage, winter injury, boxwood leafminer, and various root rots.  "Box blight" caused by the fungus, Cylindrocladium buxicola, should also be eliminated before making a Volutella blight diagnosis.  This highly destructive fungus typically causes a rapid decline of entire plants rather than sectional dieback.  If box blight is suspected, we urge that you send affected plants to our OSU Extension, C. Wayne Ellett Plant and Pest Diagnostic Clinic, for confirmation [  http://ppdc.osu.edu/ ].

Transition Zone Between Healthy and Cankered Tissue
Transition Zone Between Healthy and Cankered Stem Tissue