It looks like fire blight, you need remove any infected branches. Dip your pruner in a 10% solution of bleach and water between cuts to prevent spreading it further. Then treat it with Agristrep. I would also recommend after that treating with a biological control. Agristrep: https://www.amazon.com/Fertilome-Fire-Blight-Spray-10363/dp/B005XOPBCU?th=1&psc=1 Bio control: https://www.amazon.com/Bonide-Revitalize-Fungicide-Concentrate-Ounce/dp/B076HW6S9K/ref=sr_1_11?keywords=biological+fungicide&qid=1686275990&sr=8-11