Residual effect of atrazine on field-grown dry beans and sunflower

Abstract

The applicability of fixed recropping intervals for crops that are sensitive to atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-striazine) was assessed. Atrazine carry-over was monitored 12 and 24 months after its application at six different rates to maize (Zea mays L.) grown in eight trials at six sites. The rotational test species were dry beans (Phaseolus vulgaris L. cv. Teebus) and sunflower (Helianthus annuus L. cv. SO 222). Yield reductions indicated the carry-over of phytotoxic atrazine residues. At 12 months after treatment dry bean yield was significantly reduced at one site and sunflower yield at six, on plots previously treated with the atrazine rates recommended for maize. During the next season significant yield reductions (dry beans 38%; sunflower 29%) occurred only on the single montmorillonite soil (pH 7.8). The relatively high tolerance of the dry bean cultivar in most soils at the first assessment is not reflected in the single recropping period of 18 months that is currently recommended for both species. Current recropping intervals for sensitive crops could be refined by assigning flexible intervals that are based on the herbicide's expected dissipation rate in a particular soil, as well as on the tolerance of the follow-up crop.