If there are many onions, use pyrazosulfuron. If there are many fenugreek seeds, use bensulfuron-methyl. After taking the medicine, the water layer is 3~5 cm, and the water is kept for 5~7 days.

How long a pesticide fails after adding water depends on the kind and quality of the pesticide, and the failure time of different pesticides after adding water is also different. Different kinds of pesticides have different expiration dates. For example, the efficacy of dichlorvos is short, and it will expire in about ten hours, while the efficacy of dichlorvos is long, and it will expire in about ten days. The failure time of different water quality is different. The water quality is neutral or slightly acidic, and the failure rate is slow, while the alkaline or acidic water quality is fast.