Study On The Growth Inhibition Toxicity Of Pyrazosulfuron-ethyl Nicosulfuron And Rimsulfuron Herbicides To Lemna

Sulfonylurea herbicide is a new super-efficient herbicide widely used in rice production.Duckweed is an important aquatic plant in paddy ecosystem,it can be used to evaluate the toxicity of pesticides to aquatic plants,but the domestic test system has not been established.The study of sulfonylurea herbicides is of great significance to the safe use of pesticides.In this paper,three typical sulfonylurea herbicides,Pyrazosulfuron-ethyl,Nicosulfuron and Rimsulfuron,were selected as test agents,Small duckweed and purple back duckweed were used as aquatic organisms.The effects of pesticides on physiological indexes such as leaf number,leaf area,fresh weight and dry weight of duckweed were studied,the toxicity was evaluated.in this study,the standardized test material culture method and the test method of growth inhibition of duckweed were established,To provide theoretical basis for risk assessment of sulfonylurea herbicides.The main findings are as follows:?1?Small duckweed and purple back duckweed were collected and identified from paddy field.The biological growth of two kinds of duckweeds for 7 days was measured.The average specific growth rate of little duckweed was 0.562d^-1,and that of purple back duckweed was 0.541d^-1,both kinds of duckweeds have reached the growth requirement with a 7d average specific growth rate of more than 0.275d^-1.The biological growth amount satisfies the test requirements and the test material culture method is effective.?2?Researched and compared the advantages and disadvantages of calculation of leaf area by five methods including pigment exchange algorithm,grid comparison method,grid painting method,partial general method and leaf area analyzer method,the difference of calculate the fresh weight of the plant by centrifugal tube method and paper suction method is analyzed.Based on the economic and operational convenience of the test,the grid drawing method and paper suction method were determined as the test methods.Using the number of leaves as a test index,the growth inhibition toxicity of 3,5-dichlorophenol to duckweed was EyC₅₀?168h?=2.56 mg/L,the growth inhibitory toxicity of 3,5 dichlorophenol against purple back duckweed was EyC50?168h?=3.07 mg/L.The EyC50?168h?values of both species of duckweed are between 1 and 5 mg/L,meet further test requirements.?3?The inhibition toxicity of pyrazosulfuron,nicosulfuron and rimsulfuron on the growth of little duckweed was studied in laboratory.The inhibition rate increases with the increase of concentration,and the results show that the three herbicides can inhibit the growth of little duckweed in a certain range.?4?The inhibition toxicity of pyrazosulfuron,nicosulfuron and rimsulfuron on the growth of purple back duckweed was studied in laboratory.The inhibition rate increases with the increase of concentration,and the results show that the three herbicides can inhibit the growth of purple back duckweed in a certain range.During the test,it was found that the duckweed leaves of the suppressed group were thickened,while those of the uninhibited group were growing normally.