Laurel Hedge Dying - Fungal Disease
The shrubs look like cherry laurels.
There may be several reasons for the browning/decline such as winter damage, past fungal disease, possible scale, a sucking insect, borers, etc. You may have to do some detective work and look for this.
In general, cherry laurels grow best in a well drained soil in morning sun and afternoon shade. Has something changed in the area such as drainage, downspouts? They will not be happy in a poorly drained soil and susceptible to roots rots. Check the drainage in the area. Make sure mulch is no thicker than several inches and keep away from the base of the shrubs. Thick mulch is attractive to boring insects. Make sure they are not planted too deeply. You should be able to see the flare at the base of the trunk. Deep planting can cause bark deterioration at the soil line which eventually causes decline.
Many broadleaved evergreens such as cherry laurel have been subject to winter damage this season. This winter has been cold, with temperature fluctuations, and very dry. Be sure to water broadleaved evergreens up until the ground freezes to prevent winter damage. See our website for more information https://extension.umd.edu/hgic/winter-damage-trees-and-shrubs
Cherry laurels are also prone to scale insects such as the white prunicola scale. This is a sucking insect that can cause dieback. Monitor for these scale insects - look along the branches and stems for small disc or oystershell shapes that can be scraped off. See our website http://extension.umd.edu/learn/armored-and-soft-scales-trees-and-shrubs
At this point, the old foliage on the cherry laurel should drop off. No fungicides are needed. Simply rake old foliage up. You will have to monitor for new growth. Scratch the branches with your fingernail and look for green tissue. If you see it the branch is viable. If you see brown it is dead and you will have to prune.
Water the plants during dry periods during the growing season.
You can send us additional photos if you notice symptoms this growing season.