Wis. Stat. § 26.205: Tractors, spark arresters.

Tractors operating in a forest protection area or on other land where there is danger of setting fire, shall be equipped so that the tractors will not set fire on the lands and to reduce to a minimum the danger of setting fire. The department or its locomotive inspector is authorized and directed to reject from service all tractors not properly equipped to prevent the setting of fires. The department shall, after investigation, prescribe suitable fire preventive devices for tractors operating in marsh land or on other land where there is danger of fire being set by their operation.