What Is Buxus Blight?

Buxus Blight is a fungal disease caused by the pathogen Calonectria pseudonaviculata (AKA Cylindrolcadium pseudonaviculatum or Cylindrocladium buxicola). It first appeared in the UK in the mid-1990s which quickly spread throughout Europe. It was then reported in the USA around 2011. Now the the Department of Primary Industries in NSW has recognised Buxus Blight in Australia.

https://www.dpi.nsw.gov.au/biosecurity/plant/insect-pests-and-plant-diseases/buxus-blight

Buxus Blight infects all aboveground parts of the plant The eirst signs appear as dark leaf spots that coalesce to form brown blotches. The undersides of infected leaves will show white fungal spores, especially following periods of high humidity. Buxus blight causes RAPID DEFOLIATION, which usually starts on the lower branches and moves upward in the canopy. During periods of high humidity, white, fuzzy masses that consist of numerous clumps of spores will emerge from stem cankers. 

Buxus blight thrives in damp areas with little air movement around 15-30º C and high humidity. Leaves that are continually wet from constant irrigation, prolonged rain, or high atmospheric humidity are prime targets for the pathogen.