Boxwood leaves turning bronze - not straw- color
I know about biotic and abiotic issue resulting in straw color. This is not. The coloration start at the end tip of a sole branch, on upper branch - not lower, and turn green leaves ti bronze. eventually part or whole shrub turn bronze and be defoliate. I cannot find any dark marks on green twigs. We are in September and cannot be winter damage. The shrub were looking find early this summer. The issue is propagating to other shrubs located 100' away. Shrub are irrigated.
District of Columbia
This plant looks like an Inkberry holly. The plants look like they are not establishing and they look stressed. There may be several reasons for the branch dieback such as poor drainage, poor site conditions, poor planting techniques, etc.
We would like to have more information.
You did not mention when the shrubs were planted. If the plants were planted within the last year of planting, you may be dealing with the above.
Here is some information. Check the soil drainage and make sure there are no downspouts dumping water in the site.
Before planting, if the roots are root-bound within the container, make several cuts along the outside of the root ball and tease the roots out so they can establish into the surrounding soil.
Do not plant too deeply. Dig the planting hole deep enough to accommodate the plant with the top of the root ball level with or slightly above ground level. Mulch should be no thicker than 2-3 inches. Keep it several inches away from the stems of the plants.
Check the soil moisture of new plants weekly and water deeply. Water established plants during dry periods.
Also, in the left photo - we notice a possible leaf spot. No control. Check the drainage.
Right photo - we notice on some branches, Indian wax scale. This is a sucking insect. Look for white raised bumps on the twigs. Pick off and drop into soapy water. Prune dead branches. https://extension.umd.edu/hgic/topics/soft-scales-trees-and-shrubs
Your shrubs are struggling to get established. These shrubs are pretty adaptable to soils and can tolerate wet soils. However, you do not want downspouts dumping water in the root zones. At this point, we recommend that you make sure mulch is no thicker than several inches and keep away from the base of the shrubs. Water the shrubs during dry periods. You may have to probe with a screwdriver and make sure the soil is moist about 6 inches down.
The shrub on the right has Indian Wax Scale on the branches. Pick off and discard in soapy water. See our prior response on this sucking insect.
Prune dead branches. All you can do is monitor the health of the shrubs and look for new growth next spring.
Also, some inkberry holly cultivars tend to get leggy at the base. In this case, you may be able to plant some perennials to hide the bare branches at the base of the shrubs. Here is more on inkberry hollies http://www.missouribotanicalgarden.org/PlantFinder/PlantFinderDetails.aspx?kempercode=d553