Hi Anna,

This may be fireblight. You can prune now to stop the disease from spreading to the whole tree, but do so on a dry day.

Here's information from the University of Minnesota:

"Twigs and branches infected with fire blight can be pruned out in order to prevent the infection from spreading to the main trunk.

• Prune diseased twigs and branches in late winter when the tree and bacteria are dormant. This reduces the amount of sucker growth from wounds and eliminates the chance of spreading infections between pruning cuts.
• Make the pruning cut through healthy wood at least 8 inches below the discolored bark of a canker.
• If fire blight is seriously damaging a cotoneaster hedge, cut the hedge to about six inches above the ground in late winter. If only a few stems are blighted, they can be removed as described above.
• If pruning must be done during the growing season, sterilize pruning tools between each cut. To sterilize, spray the cutting blade with disinfectant or soak the cutting surface in disinfectant for at least 1 minute. Effective disinfectants include a 10% bleach solution and undiluted Lysol.
  • A 10% bleach solution can be made by mixing one part household bleach to nine parts water. This equals 1.5 cups of bleach to 1 gallon of water.
• Burn or bury infected cuttings.
• If the infection reaches the main trunk, the disease cannot be cured and the tree will eventually die. If this happens, it’s best to remove the entire tree along with the stump. This will eliminate one source of bacteria for the rest of the susceptible plants in the area.

Here's the link to that whole page:

https://extension.umn.edu/plant-diseases/fire-blight#prune-out-infection-1760461

I hope this helps. Good luck.