The Decision of Minimum Lethal Dosage of Isoproturon by PPM Method

摘要

The experiment was conducted in the green house in the China in order to determine the Minimum Lethal Herbicide Dosage (MLHD) of photosynthesis inhibiting herbicide, isoproturon on three weed species and safety to the wheat with Plant Photosynthetic Meter (PPM). The results showed that the PPM value of the weed leaves decreased sharply 1 day after application, and the diagnostics of weed caused by isoproturon could be observed 6 days after application. Weed growth was inhibited later on. Both PPM values of weed leaves and weed biomass (shoot fresh weight) decreased as herbicide dosage increasing. However, the susceptibility of weed species to the isoproturon was different among weed species. Descurainia Sophia and Capsella burse pastors were susceptible to the herbicide, and Alopecurus aequalis was relatively less susceptible to the herbicide. MLHD could be calculated by weed biomass 14 days after application of the herbicide. There were close relationship between weed biomass reduction rate and PPM values of weed leaves 2~5 days after treatment. This indicates that the PPM value being measured in early days after treatment could give reasonable prediction on weed control efficacy and on wheat safety. The isoproturon usually provided 85%~90% control by weed biomass when PPM value was about 20. The isoproturon usually could not injury wheat by plant height and biomass when PPM value was over 60. The MLHD of isoproturon should be the dosage when PPM value is below 20 measured for weed and over 60 for wheat on the 2~4 day after treatment.