English box brush in ground 5 years. One did same condition last Spring and...
English box brush in ground 5 years. One did same condition last Spring and was dug up. the second is going the same (started with 4 brushes). Sun in AM north side house. 2 boxes planted each side of pouch stairs. One on each side still in good condition . No evidence of voles. Leaves not curling , just turning yellow. photo attached.
This does not look like a disease or insect problem. Looks like there may be a type of root problem which may include planting techniques, environmental issues, etc. Sometimes there may be several boxwood plants growing in a container. It is possible that one of the plants root systems were affected. Boxwood can also be affected by snow and ice damage.
At this point, all you can do is prune out the affected portions. Proper pruning includes thinning. Boxwoods have growth buds all along the stem. Hopefully, the plant should put out new growth. Monitor the plant throughout the growing season for additional symptoms. See our boxwood publication for more information. http://extension.umd.edu/sites/default/files/_images/programs/hgic/Publications/HG52_IPM_Boxwood.pdf