Hi there Frank,

Thank you for reaching out to Ask Extension about Fireblight. 

Unfortuneately Fireblight is an incurable plant disease. The best way to prevent this disease is to plant resistant varieties of trees and plants.

 If you think you already have Fireblight in your crabapple, then you might be able to manage the disease, if it is not severe and only affecting a few branches. Infected plant parts should be pruned out and removed, making sure to disinfect your pruners or saw in between each cut, so you don't spread the disease between cuts, or later to another plant. Making proper pruning cuts is very inportant to encourage fast wound healing of the tree. There are also chemical sprays that can be used to help control the spread of Fireblight during the flowering season, which is best done by a professional to avoid phytotoxicity and because the timing of the sprays is critical. 

The following publication will give you more information about Firelight and how to manage it: https://extension.colostate.edu/docs/pubs/garden/02907.pdf?_gl=1

I hope this helps!

Dawn