Abstract: The aim of this study was to evaluate the weed-control effects and the persistence of the herbicide 2, 4-D butyl ester in field crops of covered oat. Covered oat (cultivar Longyan No.3) at the 3-4 leaf stage was treated with 2, 4-D butyl ester at three application rates (450, 750, and 1050 mL·ha^-1). The dissipation and residue dynamics of 2, 4-D butyl ester and its decomposition products in covered oat plants were evaluated at 1, 7, 14, 21, and 28 days after application, and at the flowering, grain filling, and maturity stages. The effects of this herbicide on weeds and on the safety, yield, and plant height of oat were investigated. The results showed that 2, 4-D butyl ester significantly affected the safety and yield of oat, but was effective in controlling weeds in oat fields. High dosages caused damage to the oat crop, such as top sagging, leaf redness, and medicine spots. The efficacy of weed control improved with increasing concentrations of 2, 4-D butyl ester. The 1050 mL·ha^-1 treatment had the strongest control effect, with up to 90% weed control at 45 days after treatment. The application of 2, 4-D butyl ester decreased oat plant height by 10.49% at the 1050 mL·ha^-1 dosage. The 450 mL·ha^-1 concentration of 2, 4-D butyl ester reduced oat hay yield, but it did not differ significantly (P>0.05) from that of the control, and improved oat grain yield by 22.64%. The 750 mL·ha^-1 concentration of 2, 4-D butyl ester improved oat yield by 40.57%. The 1050 mL·ha^-1 dosage of 2, 4-D butyl ester significantly (P<0.05) reduced oat hay yield by 8.85%. The degradation dynamics of 2, 4-D butyl ester and 2, 4-D in covered oat were positively related to the dosage of 2, 4-D butyl ester. The largest amounts of 2, 4-D butyl ester and 2, 4-D residues (0.168 and 0.011 mg·kg^-1, respectively) were in covered oats at 28 days after application of 2, 4-D butyl ester at the highest dosage (1050 mL·ha^-1), and were significantly higher than the amounts of residues at 28 days after applying lower dosages. On the basis of these experimental results, we concluded that application of 2, 4-D butyl ester at 750 mL·ha^-1 is the best treatment to control weeds in covered oat fields.

Key words: oat, 2,4-D butyl ester, residue, yield