Since no one else has answered, I'll try to help. I usually grow blueberries in soil, but I also grow lots of vegetables in containers, just not blueberries. So take my advice for what it's worth. It doesn't appear to be over fertilization, as that would affect the entire plant, but much of it looks ok. It doesn't look like pH either. From the photos it appears to be specific branches that are affected. You could check for something that's affecting entire branches such as borers, fungi and such but blueberries are usually fairly pest resistant. Considering your zone though, might be worth checking for pests or diseases that damage stems. Aluminum can be toxic at high doses (I usually use sulphur), but I don't think that's it either. If you do think you over fertilized your plant, flush it. Another possibility is root damage. I have noticed that root damage on blueberries often only affects a few canes at a time, almost like canes each have their own root system. Root damage can be caused by many things including overwatering, rot, pests, or even physical damage among other things. Blueberries definitely don't like wet feet. Maybe even frost damage since you are in a pot rather then ground. Might want to pull the plant out of the pot and take a look. Looks like you may have other plants growing in the pots. Could they be choking roots? Let us know what you find out. It's hard to tell what is going on without more info.

Reilly: I have never seen anything like that on my blueberries, so I would agree it is something relatively uncommon. However, it does look like a fungal infection, and Nick seems to be pretty sure of his ID of Phomopis Stem Wilt. I would prune off the affected parts as soon as they appear. If you have lost the insert on your fungicide, but you know at least the brand name, look it up on the internet and read about it. Copper fungicides are normally not highly toxic to humans, but you may have to choose between picking the blueberries and saving the plant. If that disease continues to progress, you may lose your blueberries anyway. If you have this disease established in your plantings, you will want to apply a fungicide much earlier next season. Don Yellman, Great Falls, VA

The bushes are planted pretty close to each other and they have a tree to deal with. To me it appears quite clearly to be nitrogen starved, in fact all 3 are starved. The reason the other two are not as light could simply be the difference in plant type or more likely it is due to that plant being in the middle so it has competition on both sides for nutrients. A good sign the plants are getting all the energy they need is large dark green leaves and new....I call them bull shoots coming from the base of the plant. You can see one nice size new shoot on the plant on the right but that is it. On young plants you want to see 2 per plant minimum and they should be pencil thick. I would strongly suggest you get some water soluble ammonium SULFATE not ammonium nitrate. Use 1 tsp per gallon of water and do that weekly giving 2 gallons per plant. Make sure the plants are not dry when you give it. The plant should green up pretty fast. The ammonium sulfate is 21-0-0. For those that say what about the other needed elements? Ignore them for now. The BB need the nitrogen constantly but only need the P and K now and then, same goes for all plants. For inground plants that are mulched there is generally enough native P and K anyway. I have not given my 200 or so in ground BB any P or K yet this year just nitrogen weekly since mid February. Potted plants are different and need more P and K added more often. One of the problems with our "soil" is fertilizer tends to wash right through. Ammonium sulfate clings tightly to the soil and resists being washed out. Here is a picture of what you want your leaves to look like. This is on one of my bushes. While those leaves may look big last year Floralcity Lou had leaves on his potted plants that were even bigger. This year I have him beat :) as he was overrun with new projects. Bet that is more than you wanted to know lol.

How are you watering this plant? Do not get the leaves wet. Use lime-sulfur spray if you can. I have never seen anything like this, so unsure? If you can't use sulfur, wash leaves off as best possible, and use horticultural oil, do not use sulfur and oil, that will kill all the leaves. You might want to post in the Orchard forum, lot's of experienced blueberry growers there.