Sadly, LuLuLand lost a member of her garden family this year to the FireBlight bacterium Erwinia amylovora. A beautiful 30 ft pear tree seemed to suddenly and quickly show up sickly with young shoots , then whole branches, turning dark brown and curling down. It was spreading rapidly so researching the problem and concluding it's cause had to be done swiftly. Unfortunately in this case most of this tree had to be cut down as it appeared that the trunk was also affected.
Cleaning up ALL fallen sick leaves in the area is important as well as using a 10% chlorine solution on your clippers between cuts . I also removed affected clippings to a burn pile a ways away.
Seems like a severe solution but it may have saved surrounding family members susceptible to FireBlight such as apples and loquats.
I learned that pollinators and other insects can spread the disease as they are attracted to an oozing substance the bacteria create.
Also, heat, humidity, and rain can promote the growth of this bacteria...we don't have any of these, do we?
Check your trees in the winter and prune as needed according to the advice given on most websites associated with university agricultural research such as Cornell, UC Davis, and Clemson. Wikipedia has some interesting history on it as well.
So what is the first permaculture principal? Observe and interact! Keep looking to observe your tree's health and make adjustments such as pruning as necessary! In this case also avoid over fertilizing and watering especially during blossom time!
I hope you don't loose any friends by not noticing there is a problem with them and regretting not taking action in time!