Hi,

The image of the fruiting shoot definitely appears to be fireblight but the random blackening of leaves on the tree is not typical, unless the entire tree is dying.  Organic management of fruit trees can be a bit challenging and really starts with variety selection on resistance.  The D'anjou is one of the more highly susceptible varieties to fireblight.  Highly Resistant varieties include: Honeysweet, Kieffer, LaConte, Magness, Moonglow, and Old Home.  Seckel, and Maxine are classified as Resistant.

It may be worth doing a soil test to see where your nutrient levels are.  Avoid over-fertilization and severe pruning as lush new growth is more susceptible to infection from fireblight and other diseases.

Pruning out infected tissue 4-6" below infection and sanitizing sheers after each cut would be the immediate control measure to ensure it does not continue to spread down the tree.  Bag all plant matter and dispose.

Copper based fungicides can be used in dormancy prior to bud break.  Copper and/or streptomycin can be used to protect new growth until petal fall.