We don't see clear symptoms of a particular ailment, but boxwoods are vulnerable to several stress factors in our area, so you can compare what you're seeing up close with the information on our boxwood diagnostic page. The pictured dieback does not look like the work of an insect or mite, even if minor outbreaks have affected other parts of the plant. The dead foliage may be from Volutella, one of our most common boxwood infections, which is not treatable with fungicide. The pathogen takes advantage of weakened plants (winter injury to branches is common, though there might be other causes) so is more of an opportunist than a virulent pathogen. Fungicide is not warranted at this point, nor is insecticide, so no treatments are needed nor would they be able to reverse existing damage.

For now, prune off all brown-leaved or bare branches and keep monitoring the plant for watering needs to reduce any drought-related stress. If a boxwood's roots remain healthy, they have the potential to regrow, though that would not generally happen this late in the growing season and would resume in spring. Do not fertilize (including via a product that combines fertilizers with pesticides) as this can add to an ailing plant's stress and worsen its condition. We can't quite tell if the soil covering in the photos is mulch chips or stone. If stone, is there landscape fabric laid underneath it? When used long-term under stone mulches (in contrast to as a temporary soil covering meant so smother weeds), landscaping fabrics might interfere with how easily precipitation or irrigation moisture reaches the roots, as well as how much oxygen the roots can access from the soil surface to stay healthy. Even if it doesn't have direct health impacts for shrubs and trees, it might allow opportunistic pests/pathogens to attack a plant under stress.

Was a weed killer (herbicide) of any type used around the shrubs in recent weeks? The pattern of damage suggests exposure to an herbicide or something sprayed on the stone/mulch/soil, but it doesn't necessarily exclude other causes. If herbicide was used, all you can do is to prune out the damage and use more caution when making applications near the boxwoods in the future.

Miri