Answer: Blueberries should be pruned during the winter while the bushes are dormant. Fruit of the blueberry is borne on wood produced in the previous season (one-year-old wood). You can remove some of the oldest, thickest canes and still have a heavy crop next year.
There's really no way to remove poison oak with chemicals if it is growing in your blueberry patch. You will have to cut the poison oak down and then dig it out of your blueberry plants. I'd also remove the wild cherry tree. While it might be fun to have it grow in your landscape, if it is growing within your blueberry patch it will grow rapidly and will shade out the blueberries which will make your crop much smaller. If you like the tree, dig it out and move it elsewhere this winter.
Best wishes with your garden.
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