Hay bales up in smoke.

Those who cut crops for hay this year will be wary after the reports of several haystack fires. These resulted from excessive humidity in the stack from moisture allowing microbial action that results in heat and spontaneous combustion. Once the stack is alight, pulling it apart if possible may allow some to be recovered, but all too often, all hay in the stack is lost or ruined. High sugar levels in many hay samples measured this year may also be a contributing factor.

The time from heating to combustion may vary from 4 to 10 weeks. Stacks can be monitored for heat by inserting a crow bar for several hours to feel for heat or by inserting a thermometer deep into the stack down a pipe. A stack should be pulled apart when 70 degrees centigrade or more, with combustion likely at 76 degrees centigrade.