Tolerance of three types of winter wheat (Triticum aestivum L.) to fluroxypyr plus MCPA ester

Abstract

Six field trials were conducted over a 3-yr period (2005-2007) near Exeter and Ridgetown, Ontario, to evaluate the tolerance of three types of winter wheat [soft white (SWWW), soft red (SRWW) and hard red (HRWW)] to three rates of fluroxypyr plus MCPA ester (54 + 281.25 g a.i. ha-1; 108 + 562.5 g a.i. ha-1; 216 + 1125 g a.i. ha-1) at two postemergence (POST) application timings [Zadoks 31-32 (POST 1) and Zadoks 33-34 (POST 2)] in the spring. Fluroxypyr plus MCPA ester applied at POST 1 caused no injury to winter wheat. Fluroxypyr plus MCPA ester applied at POST 2 caused as much as 4, 4 and 7% injury 14 d after treatment (DAT) in SWWW, SRWW and HRWW, respectively. Fluroxypyr plus MCPA ester applied at 54 + 281.25 g a.i. ha-1, 108 + 562.5 g a.i. ha-1 and 216 + 1125 g a.i. ha-1 at POST 2 caused up to 1, 6 and 10% injury 14 DAT, respectively. Fluroxypyr plus MCPA ester applied at 216 + 1125 g a.i. ha-1 (POST 2) caused as much as 5, 5 and 12% injury in SWWW, SRWW and HRWW, respectively. Winter wheat height was reduced an average of 3 cm with the high rate of fluroxypyr plus MCPA ester in 2006. There was no significant effect of fluroxypyr plus MCPA ester rate or application timing on the yield of winter wheat. This study concludes that there is an adequate margin of crop safety in winter wheat to fluroxypyr plus MCPA ester applied POST in the spring.