What are the white things painted under many trees in roadside green belts?

This is a tree whitening agent. Its main components are quicklime water, salt, sulfur and some trichlorfon. It is made according to a certain proportion. It is mainly used for preventing and controlling tree diseases and insect pests in winter, and preventing pests from climbing from trunk to ground soil for overwintering. Because more than 90% of the ingredients are quicklime water, it is white. Generally, the painting height of trees in winter is 1m ~ 1.2m high.