There are organic sprays available, for example liquid lime sulfer (calcium polysulfide) and spinosad. Bear in mind just because it says "organic" doesn't mean it's safe or environmentally responsible. Spinosad is deadly to bees and pollinators and sulfer is deadly to other beneficial insects like parasitoids. Horticultural oil is a petroleum product -- you old spray it in the winter so it's not a threat to bees, but it does kill any beneficials overwintering in the tree as well.

AFAIK, there is no effective organic alternative for streptomycin sulfate to treat fireblight.

Organic or not, you will have to develop and maintain a rigorous spray program. Going to the fruit classes at Petals From the Past can be a big help here. Dr. Arlie Powell knows pretty much everything there is to know about fruit growing in our region.