Study on the Influence of Solanum nigrum L. on Cotton Growth and Its Economic Threshold

【Objective】 Solanum nigrum L. is a troublesome weed seriously damaging cotton growth development. The objective of this study is to investigate the effects of Solanum nigrum L. on cotton growth in cotton fields and yield traits and its economic threshold, and provide a scientific basis for the formulation of control parameters on Solanum nigrum L. in cotton fields and its control measures. 【Method】 The effects of different densities of Solanum nigrum L.（0, 1, 4, 7, 10, 15 plants/m²） on cotton agronomic traits and yield traits were investigated in field conditions. Then the functional relationship between different densities of Solanum nigrum L. and cotton yields loss rate was researched by using model fitting method. Control economic thresholds on Solanum nigrum L. in cotton were derived on the basis of the economic infestation level formula. 【Result】 The plant height, stem thick and the number of main stem nodes of cotton decreased with the increase of Solanum nigrum L. density, and Solanum nigrum L. had a significant effect on the middle boll number and yield of cotton（P< 0.05）. When the density of Solanum nigrum L. is 1 plant /m², the loss rate of cotton yield is 60.92%. When the density of Solanum nigrum L. reaches 15 plants /m², the loss rate of cotton yield is 100%. The logarithmic regression model was the best in describing the relationship between Solanum nigrum L. density and yield loss as y =12.594ln（x） + 58.025.According to EIL and the logarithmic regression model, the economic threshold for artificial control of Solanum nigrum L. was 0.016 plants/m², and the economic threshold for chemical control by 96% S-metolachlor EC was 0.017 plants/m². 【Conclusion】 The inhibitory effects of Solanum nigrum L. on cotton were positively correlated with its density.According to the economic threshold analysis, when the density of Solanum nigrum L. in the field is higher than 0.016 plant /m²,it should be controlled in time.