Yup fireblight does that! Here in dallas fb is at it's worst in the spring rain. You might try fertilome on blossoms.

Fire blight is a bacteria. So conditions that favor bacteria are going to be the worst, namely warmth and moisture.

Well that must be it then. Somehow I got the idea it came during dry times? What is fertilome? Obviously Immunox does little good. Some of the other trees got a little of it, but I suppose some trees are more susceptible than others. Guess Clap pear trees are very prone to it.

around here (Raleigh NC zone 7b) Fireblight spread during spring like weather - windy, rainy, cool - and you see the signs when it warms up in summer. It takes a while for the bacteria to take hold and do damage so you won't always see it in the spring.