| Cotton aphid(Aphis gossypii)is one of the main of pests in Xinjiang cotton fields,and the economic threshold is an important index in pest control.Clarifying the economic threshold of cotton aphid control can helpful scientific use of insecticides and improve the integrated management of cotton aphid.In this paper,we studied the relationship between the damage and yield loss of two main varieties of cotton aphid in northern Xinjiang to explore the economic threshold of cotton aphid control in this region.The main research results are as follows:(1)The results of the natural growth of cotton aphid populations at different initial densities of 10,20 and 30 aphids/plant during the seedling-bud stage showed that the cotton aphid populations of both cotton varieties maintained a continuous growth,the peak population size at 15 th day.The cumulative aphid days of the three treatments of the variety "Z1112" were 8552.85 aphid-days,11380.2 aphid-days and 16823.1aphid-days,respectively.The cumulative aphid days of the three treatments of the variety "Xinluzao 74" were 6183.9 aphid-days,10316.7 aphid-days and 14043.15 aphid-days,respectively.As the initial density of cotton aphids increased,plant height,stem diameter,leaf area,internode number and boll number all showed a decreasing trend,but the single boll weight had no significant effect.Yield loss rates of "Z1112" in three treatments were 19.98%,32.67% and 45.2%,respectively.The yield loss rates of Xinluzao 74 were15.89%,33.52% and 39.06%,respectively.The initial density of cotton aphid was positively correlated with the yield loss rate.(2)The results of natural growth infestation of five initial densities of cotton aphids at the bud stage with 50,100,150,200 and 300 aphis/plant showed that the cotton aphid populations of all the other nine treatments maintained a continuous growth,and the overall growth rate of cotton aphid populations showed a decreasing trend from 18 th day in all treatments,but except for 300 aphids/plant treatment of "Xinluzao74".The population of cotton aphid in the 300 aphids/plant treatment of " Xinluzao 74" peaked on 18 th day,while all others peaked on 24 th day.The accumulated aphid days of the five treatments of variety "Z1112" were 78750.6 aphid-days,85894.5 aphid-days,104412 aphid-days,113665.8 aphid-days,123243.6aphid-days,respectively.The cumulative aphid days of the five treatments of the variety "Xinluzao 74" were 95290.2 aphid-days,101328.9 aphid-days,107761.95 aphid-days,114939.3 aphid-days and 134744.4aphid-days,respectively.With the increase of initial density of cotton aphid,plant height,stem diameter,leaf area,internode number,fruit branch number and boll number of cotton all showed a decreasing trend,while single boll weight had no significant effect.Yield loss rates of Z1112 in five treatments were 54.84%,60.45%,66.2%,76.28% and 87.38%,respectively.The yield loss rates of Xinluzao 74 were 51.93%,55.73%,61.26%,67.19% and 71.37%,respectively.The initial density of cotton aphid was positively correlated with the yield loss rate.(3)The regression equation was obtained by fitting the cumulative aphid days and yield loss rate.y=0.003x-0.63 at seedling stage of "Z1112";"Z1112" bud stage y=0.001x+0.106;Seedling stage of "Xinluzao 74" y=0.003x-0.164;The bud stage of "Xinluzao 74" is y=0.001x+0.433.The economic permissible damage level(EIL)was calculated from the means of the control cost,the control effect,the market price of cotton and the expected yield of cotton to be 1.93%.The cumulative threshold of aphid days for the control of cotton aphid was obtained.The seedling stage of "Z1112" was 853 and the bud stage of "Z1112" was 1824.The seedling stage of "Xinluzao 74" is 698 days,and the bud stage of "Xinluzao 74" is 1497 days.The threshold of aphid quantity was calculated as follows: 240 head/plant at seedling stage of "Z1112" and 295 head/plant at bud stage of "Z1112".The seedling stage of "Xinluzao 74" was 193,and the bud stage of "Xinluzao 74" was 248. |
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