Recently moved into a home with established boxwoods in good health. One developed a small patch (few stems) of yellow leaves in April - assumed winter trauma - but the patch has spread and turned brown. Looking inside the shrub, the stems have died. Wondering if this is root rot and if removing the affected stems and amending the soil will save the shrub. This shrub is not in the same bed as other boxwoods but the property has multiple hedges of them.