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Persistence of Carbofuran and its Metabolites, 3-Keto and 3-Hydroxy Carbofuran, under Flooded Rice Culture¹

ABSTRACT

Pesticides are essential for the economical production of rice in the Gulf Coast region of Texas, since weeds and insects could severely damage the crop if uncontrolled. However, water quality of surface impoundments and estuaries interspersed in close geographic proximity to the rice belt could be adversely affected by pesticide loading via irrigation return flow.

Field experiments were conducted under flooded rice (Oryza sativa L.) culture to evaluate residual levels of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl-N-methyl carbamate), 3-keto carbofuran (2,3-dihydro-2,2-dimethyl-3-keto-7-benzofuranyl-N-methyl carbamate), and 3-hydroxy carbofuran (2,3-dihydro-2,2-dimethyl-3-hydroxy-7-benzofuranyl-N-methyl carbamate). Treatments consisted of two rates of carbofuran (0.56 and 3.35 kg/ha) superimposed two irrigation management schemes (intermittent and continuous flow).

Results of the 3-year field and laboratory study suggested that carbofuran was dissipated from the plot water via an adsorptive mechanism. Carbofuran applied at the recommended rate was generally dissipated within 96 hours following its infusion into the plot water. The evaluation of carbofuran persistence was complicated by surges in plot water values corresponding to rainfall events, although statistically significant quantities remained for longer periods of time in those plots which had received the excessive application rate. Irrigation management was not a significant source of variation once values were normalized to account for the variable plot water depths. Neither 3-keto nor 3-hydroxy carbofuran were detected in excess of 0.001 kg/ha at the recommended application rate.

Key Words: furadan • pesticide • irrigation return flow • chemical alteration

¹ Contribution of the texas Agric. Exp. Stn. and the Texas Agric. Ext. Serv. This work was sponsored in part by USEPA Grant no. S802008.

² Research Scientist, Dep. of Soil and Crop Sci., Texas A&M Univ., College Station, TX 77843; Agricultural Chemist, Texas Agric. Ext. serv., College Station; Assistant Professor, Texas Agric. Exp. Stn. at Beaumont, Texas; Associate Professor, Dep. of Soil and Crop Sci., Texas A&M Univ., College Station.

Received for publication February 8, 1978.