Shrub dogwood species can contract a few different leaf infections, though usually they aren't too serious with regards to long-term plant health impacts (even if they create an eyesore in the meantime). Powdery mildew is one possibility, though it's hard to tell from last year's photo if that was the main culprit. In either case, pruning for better air circulation by removing some crowded stems is a good step, and aside from just checking the plants for watering needs, there isn't much else you can do. Removing any leftover fallen leaves (which it looks like you either already did or don't need to do) in case they harbor infectious spores will reduce the risk of new early-season infections, and mulching exposed soil so any spores resting on the surface don't splash up onto leaves can also help (plus cut down on weed growth).

Although some leaf infections can be suppressed with fungicide, we generally discourage fungicide use. For one, it doesn't always work and it usually needs regular reapplication (potentially once every 1-2 weeks) for as long as the weather conditions are conducive to infection, which for some fungal diseases could be a significant portion of the growing season. If rain, wind, or high temperatures interrupt the spray schedule, it could give the fungus an opportunity to start an infection, as fungicide cannot cure existing disease, only prevent new infections on healthy growth. Additionally, even though such sprays target fungi, they can also affect other organisms, including pollinators; the flowers on dogwoods are visited by insects (and the resulting berries, if they're pollinated and not pruned off, are appealing to birds).

If you decide to try a preventative fungicide, sprays will probably need to begin soon now that the leaves are emerging, and the product label should include powdery mildew and other "leaf spot" diseases (it might not list them all specifically, but could include Septoria, Botrytis, and Elsinoe) among the diseases it controls. Follow all label directions, and make sure the plants are not drought-stressed when treated since that increases the risk of phytotoxicity (plant tissue damage from chemical exposure).

Redtwig dogwoods are sensitive to the roots getting too dry, and we're still in a drought that carried over from last year. Drought stress can also predispose them to Botryosphaeria canker, a different fungus than those causing leaf spot, which kills branches; this impact will be visible as browned or blackened wood on twigs the same age as those that are normally red-colored. Affected branches would need to be pruned off in that case.

If the leafless shrub doesn't produce new growth on the branches by, say, late April, the buds might have been lost due to winter drought stress or residual infection damage. If the roots are healthy and stored enough energy, they can produce new stems if the old stems have to be cut down. Otherwise, that one shrub may need to be replaced if it succumbed to too much stress or damage, but for right now, it's a bit early to make that determination.

Miri

Thank you for the additional images and information.

Regarding the close-up picture of the shrub's base: the less-red coloration of older wood is normal, as only the youngest stems have bark with vibrant color. There are a few twigs that have a darker brown base which appear to be dead and can be pruned off. We've marked some examples of them in blue lines in the modified photo attached.

Of greater concern, though, is that we can now see scale insects on the bark (green circles drawn on the photo), which weren't visible in earlier pictures. Scale insects often don't look very different when they are alive versus dead (since dead scale don't fall off the plant right away), so we can't be certain they're alive, but we see two different life stages (or possibly two different species, it's hard to tell), which suggests a population is still viable. Scale species often have a wide host plant range. White Peach Scale can feed on redtwig dogwood, and might be the round whiteish species seen on the basal bark. Cottony Camellia Scale has a different appearance and overwintering juveniles or females that haven't laid eggs yet might be what we see on some of the branch bases (the more elongate, pale brown ovals).

Whether the scale are numerous enough that their feeding (on sap) is causing any dieback we can't say, but if they prove to be abundant as you inspect that plant's bark, you may want to replace the shrub just to be safe, as treating scale can be difficult if you want to avoid using insecticides.

There are several cultivars of variegated-leaf redtwig dogwood, but the forms most widely sold like cultivars 'Ivory Halo' and 'Eleganitissima' are species Cornus alba, Tatarian Dogwood, which is non-native. Our native redtwig species is Redosier Dogwood (Cornus sericea / stolonifera), with a few cultivars of other species (which, as far as we've seen, are not also variegated) having reddish stems. We're not aware of a white-variegated variety of native redtwig dogwood on the market (there is a version with yellow stems), so the plants pictured might not be native.

Miri

Cherrylaurel tend to get White Prunicola Scale (which does look nearly identical to White Peach Scale), but perhaps the two presences are related if their host plant ranges overlap enough. The same approach, if you wanted to try treating it with horticultural oil, should work in this situation, although the shrub might have dieback due to other causes that make that approach not worth the effort (up to you).

Good luck -

Miri