If they are Spotted Dog Laurel (Aucuba japonica) this is perhaps because of their roots getting too wet. Our wetter winters seem to be the problem, at least initiating and helping the spread of the agent (a bacterium I think). The last time I looked into this problem, feeding was about the only thing mentioned to help. Clean secateurs between plants too or you can spread it.

Yes, unfortunately, I have the same thing happening with mine and my neighbours. I've cut them back heavily, fed them, mulched them....and STill it is back again in the stems. I don't know what else to do, to be honest! Incidentally, I have a small specimen right at the back of a huge Choisya...just keeping it there until I need it...and it is in perfect condition. Good point, Fractal, about secateurs etc...never thought of that...DURR!