A disease pathogen is not causing the damage to your cherry laurels. It is an insect pest called white prunicola scale. This pest is difficult to control. They are insects that feed on the plant sap and unfortunately, are a very common problem on cherry laurels. We see infestations like this a lot.

First, read through our webpage to understand the life cycle, which will help you target sprays if that is the course you want to take. https://extension.umd.edu/resource/armored-hard-scale-trees-and-shrubs

Prune out any dead, dying, or heavily infested branches and dispose of them in the trash.

Begin with a dormant spray when temperatures get cooler, later in October. Look for directions on the label of a horticulture oil product. 

For a moderate infestation, use horticulture oil again or soap sprays on crawlers (the juveniles) in May, June, mid-July to mid-August, and again in September of next year. (There are 3 generations a year, so they will keep hatching into crawlers.) When there are highly concentrated infestations on branches like you have, scrub them off with a soft brush (not wire) then spray. This knocks off their protective cover (their "scale").
Avoid highly toxic insecticides in order to preserve the beneficial insects which will help you keep this pest under control.

Deb