It is the deer’s breeding time and dogs might pose a threat to wildlife, especially young animals.
In the cantons of AG, LU & ZG dogs must be kept on a leash at all times and are never to be left unattended to prevent them from disturbing the wildlife, including barking at wildlife.
This is in effect till July 31st in/close to forests.
Also the dogs are not allowed to play on agricultural land till October 31st.