Hi Henry,

Is your blueberry bed located near any fir trees? Witches broom is caused by a rust fungus that also infects fir trees, which then spreads to blueberry bushes. If you have fir trees it is recommended that you do not plant blueberries within 500 yards of them. The article below includes pictures of what the rust fungus would look like on your fir trees as well as additional helpful information. When replanting blueberry bushes just consider their proximity to fir trees, and be watchful as the witches broom will likely not appear the first year even if the plant becomes infected. 

Blueberry witches' broom | UMN Extension

Witches’ Broom of Blueberries - Cooperative Extension Publications - University of Maine Cooperative Extension (umaine.edu)

I hope that this information is helpful. Thank you for reaching out to the UVM extension master gardener hotline. 

All the best,

Hi Henry, 

From the University of Maine article linked there is some hope that the cultivar 'Rancocas' could have some resistance but needs to be studied further. 

"Although susceptibility to witches’ broom appears to vary among different blueberry varieties. At this time the only cultivar thought to have resistance is 'Rancocas'. However, this has yet not been adequately studied."  Reference at this link: https://extension.umaine.edu/publications/5066e/

And yes, it is spread by wind but also the fungus can stay in the same area for many years. Here is some more information from the articles on the lifecycle of witches broom. 

How does witches’ broom survive and spread?

• Witches' broom is caused by the rust fungus Pucciniastrum
  goeppertianum.
• This fungus spends half of its cycle on blueberry plants and half of its life cycle on fir trees.
• Spores are produced on infected fir needles.
• These spores are carried by wind and infect nearby blueberry plants.
• The fungus grows into the bark of the blueberry plants.
• The whole blueberry plant becomes infected.
• The fungus lives in the blueberry plant for many years.
• Each spring, spores are produced on the blueberry witches' broom.
• These spores then infect fir trees.

Remove infected plants

• Fungicides can’t cure the plant or prevent new infections.
• Pruning out witches’ brooms will reduce the symptoms of the disease only for a short time. The fungus will remain in the plant's bark, and new witches’ brooms will form.
• Infected blueberry plants should be dug up and burned, buried, or composted.
• You don't want to plant blueberries in the same area unless you know the fungus is cleared and that can take many years

I hope this is helpful! 

Thank you,