Taanit, Chapter Three, Mishnah Five
In the previous mishnayot we learned of situations in which the people of the town effected by the plague fast and sound the shofar and the people in the neighboring towns do not fully participate. In our mishnah we learn for certain plagues, not only the people of the town directly effected participate, but also the people of all the surrounding towns as well.
For these they sound a blast in all places: for the drying up of crops (shidafon), for plant disease, for locusts, and for the hasil (a type of locust), for wild beasts and for the swordthey sound a blast for these are plagues likely to spread.
All of these plagues are likely to spread; therefore, even though they may have directly effected only one part of the region, everyone must fast and sound the shofar.