use of tank-mix adjuvants to improve effectiveness and persistence of chlorpyrifos and cyhalothrin formulations

the use of adjuvants enhances the insecticide efficiency and increases the persistence of insecticides. in this study, the effect of adjuvants on the toxicity of chlorpyrifos and cyhalothrin formulations were investigated under laboratory and field conditions. the comparative toxicity of two chlorpyrifos [(48% emulsifiable concentrate (ec)] formulations (dursban and pyrifos el nasr), two cyhalothrin (5% ec) formulations (halothrin gold el nasr and lambada mox) and two adjuvants (top film and tritone k) were examined against the second and the fourth larval stages of spodoptera littoralis. the effect of adjuvants on the toxicity of chlorpyrifos and cyhalothrin formulations were investigated under laboratory and field conditions. the results showed that dursban exhibited the highest toxicity against the second and fourth larval stages of s. littoralis with lc50 values of 0.2 and 1.11 mg l-1, respectively. in contrast, pyrifos el nasr had the lowest toxicity against both larval stages. the results of joint toxic effect between adjuvants and insecticides indicated that adjuvants revealed potentiating effect on the toxicity of four insecticide formulations as co-toxicity factor values were greater than +20. mixing the adjuvants with chlorpyrifos and cyhalothrin formulations in spraying tank before application of insecticides in field strongly increased the toxicity and the persistence of insecticides. cyhalothrin formulations mixed with adjuvants gave continued significant mortality through 21 days, while chlorpyrifos gave continued significant mortality through 15 days of treatment. however, chlorpyrifos and cyhalothrin formulations without mixing with adjuvants gave significant mortality through 3 to 4 days of treatments. these results indicated that adjuvants increased efficiency and residual effect of chlorpyrifos and cyhalothrin commercial formulations. therefore, the adjuvants can be used for reducing the number of applications in the season and the application rates of insecticides.