Variegated cultivar of Aucuba japonica. The narrower stems that have gone black are going to die back to the point of attachment but otherwise you are liable to get new sprouts coming out of the shrub pretty soon.

Aucuba is a shrub so if you are hoping to persuade it to grow in tree form you will be disappointed. It looks as if you cut it back because it outgrew its space right up against the fence. Maybe it is just in the wrong place? You could grow some new ones from cuttings and plant them in better positions.

Aucuba is generally a pretty robust shrub. They are somewhat prone to this kind of dieback under cold, humid wet conditions especially if soil does not have good drainage or if there is inadequate air flow. Cut out anything dead, may come back nicely. Any kind of weather condition that might have been a trigger? With mine, I do occasionally prune out some of the denser growth to improve ventilation. Was the plant already in decline when you decided to prune it? It did well in the site previously over the years?

Here is a link that might be useful: Aucuba dieback

Thank you so much for all your responses. I will definitely take into consideration of trimming below the dieback areas on the branches. It's great to know the species/name of the shrub too.

For the past decade the shrub has grown to at least 7-8 feet tall in my backyard. The plant is over 20 years old and it has been growing very well. It has grown so big that we decided to trim it. We trimmed a lot of the branches as you can see from the photo, and then the black dieback began to slowly appear on many of the branches. We were scared that we had trimmed away too many of the branches with the leaves on it, hence it is lacking nutrients, but that is our guess.

We live in Vancouver, so we get a lot of rain year round. Right now, it's hot and sunny for the summer.

Should I trim all the black dieback areas? And since it is a shrub, should I trim everything so that it is shorter and not as tall?

Thanks everyone for your help! Much appreciated.

It's up to you if you want to keep it shorter or let it to to 10 + feet. But yes, definitely cut out all dead tissue back to good wood--you will know. (Your Aucuba still has enough foliage to recuperate.) By the way, if you think the particular site you have it is not good, you might be able to transplant it. Mine went through several transplants from house to house, site to site, until it reached it's final position. Looked for a place protected from subarctic winds, blazing sun, hungry deer which LOVE it, etc.. Found a location on the northwestern corner of the house, protected and watered by the outdoor shower area. I trim the bottom to keep the deer away and now they can't reach the foliage--even looks 'treelike'! Looks terrific now several years later but you should have seen it before I last moved it, with foliage sun burned from Winter sun, deer eaten and then the rot setting it. It started to recover almost immediately! I would say, here at least, they appreciate some protection from cold (and hot) winds, strong sun, adequate moisture and good ventilation. If per chance it does not make it, don't beat yourself up over it. Go out and buy another. Love these shrubs! Good luck!

P.S., some sites advocate raised beds for Aucuba to facilitate drainage. Might be an advantage in Vancouver's chilly, wet Winter. --Here the winters can be much colder but lots of sun too so maybe that helps with drying out in the cold season.

Just a side note -
Haven't had any luck with Aucuba here - winters are too cold. But...when I looked at the picture it reminded me of dieback in redtwig dogwood due to canker disease. You also mentioned that it began to spread after pruning. I Googled it and sure enough, Aucuba is subject to a canker disease. The point being, if you prune on the plant and it IS indeed canker, sterilize your clippers between cuts with 10% bleach solution or rubbing alcohol to prevent the continuing spread.

hortster

Great suggestion regarding sterization of tools!

Thank you everyone for your tips and advice! I really appreciate it. I will do the best I can to save it!