The poor growth and decline looks like an establishment issue and not due to insect or disease problems. Reasons may be due to too much moisture, not enough moisture, poor planting techniques, planting too deeply, excessive mulch, poor drainage, etc.

Here are some issues to look for. If the plants were container plants, sometimes the roots are rootbound within the container. If so, it is helpful to make several cuts along the outside of the root ball and tease the roots out so they can establish into the surrounding soil. If root bound, it is difficult to keep the root ball watered and the plants are not able to establish.  If the plants were balled and burlapped, were the cords removed and burlap cut loose. 

Planting too deeply and excessive mulch can cause decline - look around the base of the shrubs. You should be able to see the flare at the base of the trunk where it joins the root system. In some cases soil is piled up around trunks at the plant nursery prior to digging the trees for shipment. We do not see a root flare around the base of the trunks. All you can do is remove excess mulch or soil from the circumference of the trunk to the point where the trunk flares out into root growth.

Excessive mulch - Mulch should be no thicker than several inches and away from the base of the trunks.

Drainage - Cherry laurels do not like a heavy clay soil that drains poorly. Excess soil moisture reduces oxygen in the soil, damages fine root hairs, and the root system is unable to absorb water. We see a downspout in the photo. If the downspout is dumping water in the root zone of the plants, you may need to divert to another location away from the root zones. Check the soil drainage.  

Watering - Check the soil moisture about once a week for new plants especially during dry periods. Water deeply if needed. Move the mulch aside and check the soil moisture by probing with a screwdriver about 6 inches deep and feel with your finger. Soil should be damp to the touch. Let the soil dry before watering again. Check the soil moisture all the way up until the ground freezes this season. Once plants are established, check the soil moisture and water during dry periods. See watering guidelines. https://extension.umd.edu/resource/watering-trees-and-shrubs

At this point all you can do is look for the above issues and correct if need be.  Remove the dead cherry laurel and replace. Here are our pages on why trees and shrubs decline, planting trees and shrubs, and our blog on how to grow cherry laurels in the landscape. 

Marian