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.

In your zone, fall is approaching and the light has become less intense, so it's naturally slowing down - you will need to bring it indoors in another 6 weeks or so.

luis_pr, thank you so much. I didn't think they were spider mites at first (because it didn't look like the pictures from that link), but now I think it's very possible, since there are tiny webbing (like dirtier spider webs) covering some of the leaves of my plant.

@sharon2079 @joeywyomingzone4 Thanks guys, I was also thinking it looks like symptoms after watering too much and roots rot. but the soil looks wet because the photo was taken just after watering, before that, the plants was transplanted and watered 8 days ago, and during these 8 days, they got no watering, so I don't think the soil is too wet(during these days)?(considering the pots are not large, 8 days should be long enough for water to dry out?) Before watering I poke my fingers into the soil and at least the top 3 cm soil are totally dry.... @sautesmom Sacramento I know this brand, but most foreign plant brands are doing their business in China by using Chinese agencies, so not many people in China know Monrovia. @K S 7b Little Rock (formerly of Seattle) place for plants in China is very limited(especially in big cities), most people grow rose in balcony and we only use small pots...