Screening The Suitable Acaricide For The Root Zone Application And Its Distribution In Cotton

The spider mites have a wide host range and spread to variety commercial crops and fruits, which can cause significant yield losses in many crops. The prevention and control of the spider mite is still mainly relies on chemical control in present. Because the spider mite is highly hiding, high reproductive potential, haplo-diploid sexual reproduction and short life cycle, mainly concentrated on the back of the leaves and caused damage. It results in that spraying pesticides can not play a direct contact action to them. In this paper, the spraying treatment, leaf dipping treatment, water treatment and soil treatment were used to determine the toxicity of some pesticides to the spider mites in order to acquire some pesticides being highly effective to the two cotton spider mites. Using residue analysis methods to analyse persistent dynamics of chlorfenapyr and pirimioxyphos in cotton roots, stems and leaves with soil treatment. Main results showed as follows:1 According to the reported, thirteen pesticides which had active to the spider mites were chose to determine their bioactivities to Tetranychus urticae Koch and Tetranychus cinnabarinus Boisduval through spraying treatment at the concentration of 500 mg/L after48 h, the results showed that the dimethoate as the control, it’s corrected mortality of T.urticae and T. cinnabarinus were 62.12% and 77.78% respectively. Chlorfenapyr,dinotefuran, fluazinam, pirimioxyphos, spirotetramat, benomyl, pymetrozine, diafenthiuron and thiamethoxam had high activity than dimethoate to T. urticae, their corrected mortality respectively were 100%, 96.66%, 93.99%, 93.67%, 83.14%, 77.62%, 72.51%, 65.00% and63.36%. To T. cinnabarinus there had six pesticides including chlorfenapyr, benomyl,fluazinam, pirimioxyphos, spirotetramat and thiamethoxam, and their corrected mortality were 100%, 100%, 100%, 95.41%, 92.75% and 79.26%, all higher than dimethoate’s77.78%.2 All the pestticides of screening out by spraying treatment were further screenthrough leaf dipping to T. urticae and T. cinnabarinus, the LC50 value of chlorfenapyr and pirimioxyphos to T. urticae were 3.68 and 77.18 mg/L, had significant difference with dimethoate’s 166.24 mg/L, while the LC50 value of chlorfenapyr and pirimioxyphos to T.cinnabarinus were1.64 and 16.17 mg/L, more higher than dimethoate’s 29.85 mg/L.3 Chlorfenapyr and pirimioxyphos were chose as two high activity pesticides to have further research according to the above result. The bioactivities of chlorfenapyr and pirimioxyphos to T. urticae and T. cinnabarinus were measured by water treatment on cotton. The LC50 value of chlorfenapyr to T. urticae at 3, 5 and 7 d were 1.17, 0.57 and 0.56mg/L; pirimioxyphos’ s were 21.22, 8.22 and 5.27 mg/L; and dimethoate’s 50.14, 17.57 and6.49 mg/L when it was the control, while their LC50 value were 0.69, 0.52 and 0.14 mg/L;9.77, 5.81 and 3.81 mg/L; 16.67, 6.20 and 4.02 mg/L to T. cinnabarinus respectively. Those dates indicated that chlorfenapyr and pirimioxyphos had higher toxicity than dimethoate to the two spider mites, so they can be treated as the primier pesticides to root zone application.4 Further more researched by soil treatment to the two spider mites, after treatment 3,5 and 7 d, the LC50 value of chlorfenapyr, pirimioxyphos and dimethoate to T. urticae were1.10, 0.60 and 0.32 mg/kg; 2.64, 1.16 and 0.94 mg/kg; 10.75, 6.26 and 4.43 mg/kg respectively. To T. cinnabarinus, the LC50 values were 0.58, 0.20 and 0.17 mg/kg; 1.65,0.83 and 0.73 mg/kg; 23.73, 12.30 and 8.94 mg/kg. Chlorfenapyr and pirimioxyphos were more effective than dimethoate to control the two spider mites, as they were systemic pesticides, maybe they can be used in the drip irrigation system to control the cotton spider mites.5 The pesticides(chlorfenapyr, pirimioxyphos and dimethoate at the concentration of50 mg/L) were smeared on the cotton tissue to test the movement of pesticides from treated side to untreated side of leaf or leaves above and below the treated part was determined indirectly using the mortality of mites as an indicator. The results showed that all the 3pesticides had significant acropetal movement, dimethoate and pirimioxyphos had a certain basipetal movement, but chlorfenapyr had no.6 Absorb and distribution dynamics of chlorfenapyr and pirimioxyphos in cotton was examined through root zoon application, respectively. Along with the time going afterapplying chlorfenapyr and pirimioxyphos by soil treatment, the trend of the persistent amount of them were increased at first and then decreased in cotton, chlorfenapyr reach the maximum value at 2 d, pirimioxyphos’ s were at 5 d, then both of them decreased. The the persistent amount of the two insecticides all were roots>stems>leaves. There still had chlorfenapyr and pirimioxyphos can be detected in cotton at 30 d after treatment. The ratio of the content of chlorfenapyr in cotton leaves and stems to roots became bigger and bigger with the decrease of the concentration, can be as high as 1.3~1.5-fold, while pirimioxyphos were 0.1~0.3-fold and remained stable. These results showed that chlorfenapyr and pirimioxyphos could be moved from the cotton root to the top leaves of cotton and persistently conducted. They had a long effective to the mites.