I have a thornless blackberry bush with a vine growing into one thick 3-inch vine with lots of leaves and no fruit. The other vines have fruit. What kind of a growth do I have?
This sounds like a witches broom. They have many causes. This article will explain more: https://www.gardeningknowhow.com/ornamental/trees/tgen/witches-broom-disease.htm
Blackberry is 2 years old. Tied along fence last year. Where and what do I prune?
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
I have a 3 or 4 year old blackberry bush that I've never pruned. Every year new growth & lots of blackberries come back on the old 'branches', EXCEPT this year. We had a rough winter and it's like my bush decided to just start over and I have new growth coming up from the ground and a bunch of bare branches above it. Should I cut those old branches back? And if the answer is yes, can I do it now or should I wait 'til the end of the season?
Here are some pointers on blackberry pruning. https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Of course, if you have dead branches on your bushes, you can cut them back anytime.
Planted them 15 days ago. No signs of life yet. They were bareroot.
You should be seeing signs of life soon. Gently bend a cane or two. If the canes are still pliant, it is still alive and you should wait longer. If the canes are brittle and break, they are dead.
Some of my cultivated blackberries will have whiteish seed/pulp pieces among the ripe, black ones. What is causing this?
It sounds like white drupelet disorder, which is common in both raspberries and blackberries. Here is more information: https://www.gardeningknowhow.com/edible/fruits/raspberry/white-drupelet-syndrome.htm
I have raspberries and they would take over the yard if I let them. Wondering if Blackberries are the same.
There are probably hundreds of varieties of blackberry, some of which could be rampant and invasive in your area, and some of which are not. For information on which would be good cultivars to plant, and where to get them, you can consult your county Extension Service. This link will help you find one: https://www.gardeningknowhow.com/garden-how-to/info/what-is-extension-service.htm
Here's an article on pruning berry bushes (would apply to red raspberry also): https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
An alternative is to plant berries in containers: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
I just moved to a home north of Charlotte, NC and there are a lot of untended blackberry bushes that I would like to trim back to encourage healthy growth next year. Is it too late in the year to do this without hurting the plants?
Generally, pruning is done in spring or late summer, but since the plants are overgrown, you can go ahead and shape them up now and then begin other forms of pruning once spring arrives to get the bushes back where they should be and producing for you. This article will help with that: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm