Hello Josh,

Winterburn is sometimes relatively unavoidable due to the vulnerabilities of certain evergreens coupled with winter conditions outside of your control, but sometimes the risk of occurrence can be reduced by monitoring the watering needs of evergreens in autumn and winter (during thaws) to make sure the roots are adequately hydrated. Buffering the wind a bit with a breathable screening material like burlap or floating row cover might work well, but we don't have scientific evidence that topical treatments like Wiltpruf work well enough to be worth the effort of use.

For monitoring watering needs (at any time of year), feel the soil around five inches deep next to the plant's root zone and water well when it's becoming somewhat dry to the touch at that depth. Boxwoods have relatively shallow roots that can be more prone to stress during dry spells and a full sun exposure (which increases the moisture demands on the foliage), but similarly are not very tolerant of staying too consistently wet/soggy. Roots compromised by over-watering can also lead to a greater vulnerability to infections and conditions like winterburn because they are unable to function properly to keep the leaves and branches hydrated and nourished.

Is any ice-melting salt (not necessarily sodium-based, but any formulation) used on the nearby walkway in winter? If so, salt "burn" might be contributing to the winterburn symptoms, even though some formulations are gentler on roots than others. Doing what you have been doing so far -- trimming off burned foliage -- is the only recourse once it manifests. It looks like mulch is used here, which is good, but you can increase its total depth to about three or four inches for the winter with the goal to insulate the plants' roots from drastic temperature swings and moisture evaporation. You can then reduce it to more like two or three inches during the growing season.

Volutella is a common fungal ailment of boxwood, and while we don't see clear signs of it in the photos (perhaps because you've been removing symptomatic branches), it's certainly possible this is one agent responsible for their struggles. We do see signs of a high boxwood mite population given the heavy stippling on the foliage, so that might need addressing (even though normally they don't when causing less damage). Is there any insecticide use, either for garden pests or for mosquito aerial treatments, regularly used in this part of the yard? We ask because mite outbreaks tend to follow such pesticide use since many insecticides kill off predators and competitors of the mites, allowing them to flourish as a secondary pest.

If you haven't been using pesticides, then perhaps it's just the vulnerability to mites of this particular cultivar coupled with environmental factors promoting their survival. These include the dense growth promoted by shearing the hedge (as opposed to thinning it, which allows for better air circulation and light reaching the shrub interior), which can also lead to more frequent or extensive fungal infections. If you irrigate the garden bed, make sure it's either done early enough in the day so the foliage can be dry by nightfall, or better yet, avoid wetting the leaves entirely and water only the soil surface, since splashing water can be one way fungal spores spread. Volutella is not usually treated with a fungicide, nor would one cure any existing infections, so just keep trimming out any stems showing dieback symptoms.

Miri

You're welcome.