The Difference Between Spring and Fall Allergies

What are the differences between spring and fall allergies in Northern California? Are there different triggers?

The mechanism for spring and fall allergy is the same but the triggers are different.

Spring allergy in Northern California is mainly caused by tree and grass pollen.

The main seasonal fall triggers are weed pollen and mold. There are several molds that like to grow on decaying crops, such as the tomato fields, and these become widely aerosolized during the late summer/fall harvest.