My blackberry plants (planted in spring 2008) have recently developed a white cotton-like attachment to the underside of some of the leaves. Should I be concerned? If yes, how do I treat?
It sounds like you have spider mites. This article should help: https://www.gardeningknowhow.com/plant-problems/pests/spider-mite-detection-and-spider-mite-natural-control.htm
Many of the berry bushes on our property are turning brown and yellow with dark spots, and I notice that the trees die. I thought it was a rust and was cutting it out when I saw it to try stop it from spreading, but I'm not sure what it is. Any idea?
It sounds like it may be leaf spot. This article will help you:
http://www.ipm.ucdavis.edu/PMG/r71100611.html
My blackberry bushes are two years old and produced berries this year. I would like to prune them. Do I cut the main bush downto ground level or just cut the limbs off of main cane for winter?
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Our blackberry bush is fanning out in all directions. Should we cut these back?
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Last year I planted one blackberry bush. This year we got three berries and that is all. Do I need to plant another blackberry bush for cross pollination?
While most blackberry bushes are self-fertile, a few cultivars work better when planted near another variety of blackberry.
This article will help wtih growing blackberry plants: https://www.gardeningknowhow.com/edible/fruits/blackberries/growing-blackberry-bushes.htm
We have a lot of wild blackberries (and raspberries) growing on our property. I have been pulling out canes that are dead--sometimes having to cut them off near the ground. Since the blackberries are just about done for the season, I need to know about the plants that produced this year. Can plants that produced berries this year be cut down or will they produce berries again next year? These bushes produced so many berries this year that we ended up giving them away. We are still finding berries that are ripening even though we thought the season was over.
Here is an article that you may find helpful: https://www.gardeningknowhow.com/edible/fruits/blackberries/blackberry-pruning.htm
Our blackberries had lots of blossoms this spring but really didn't fruit much. This spring there were more blossoms than we have ever seen before. We were really looking forward to a bumper crop, but have hardly gotten any fruit. They look very healthy. We had a wet spring, followed by a humid and hot July and then we have been dry for a 4 week period. We have never fertilized them and they have been in the ground for 4 years. Thanks.
This normally happens due to pollination issues. Very wet weather or very hot weather (which you had both of) can affect pollination. These articles will help with attracting more pollinators to your garden, which turns those blossoms into fruit:
https://www.gardeningknowhow.com/garden-how-to/beneficial/insect-pollination-process.htm
https://www.gardeningknowhow.com/garden-how-to/beneficial/creating-a-pollinator-garden.htm