Application before and after germination of weeds can form a layer of anti-leaching drug earth on the soil surface, and maintain the activity during the whole growth period of the crop. When the weeds germinate through the young shoots or the root system of the medicinal soil layer, they can absorb the agents. The agent has the effect of inhibiting the carotenoid biosynthesis. The carotenoids in the weed plants that absorb the medicinal agents are reduced, causing the chlorophyll to be destroyed and the cell membrane to be broken. The grass showed decoloration or white buds, and the whole plant died of wilting. The speed of death is related to the intensity of light. Light intensity is fast, and light is slow.