Good Morning,

Looks like winter damage.  Winter damage to boxwoods is often indicated by a “snowline." Foliage that was protected by snow from wind and severe cold will remain green, while exposed parts of the plant will be brown.  

For evergreens such as arborvitaes, boxwoods, junipers and yews, prune out dead, brown, damaged or dying tissue in mid-spring after new foliage is produced. If new foliage has not yet emerged by spring, scratch the bark on affected branches and look for green tissue underneath.

Winter injury or boxwood blight? - MSU Extension
Winter Burn – Wisconsin Horticulture

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