Spring wheat tolerance to DE-750 applications was studied in Balcarce, Argentina, during 2002 and 2003. Rates of DE-750 evaluated were 6 and 12 g ae/ha tank-mixed either with metsulfuron at 4 g ai/ha or 2,4-D at 240 g ae/ha and applied at three different Zadoks growth stages: Zd 15/22, Zd 16/23, and Zd 32. The first two Zadoks stages corresponded to Nerson's elongated apex with two or more visible primordia and the glumes differentiation stage, respectively. Dicamba plus metsulfuron and picloram plus2,4-D were included as comparative treatments and applied at the same growth stage. In both 2002 and 2003, Baguette 10 tolerated the DE-750 plus metsulfuron and DE-750 plus 2,4-D mixtures sprayed during the first two applications (Zd 15/22 and Zd 16/23). However, DE-750 plus metsulfuron (12 g/ha + 4 g/ha) and DE-750 plus 2,4-D (6 g/ha + 240 g/ha and 12 g/ha + 240 g/ha) sprayed during the last application (Zd 32) caused significant yield reductions in the 2002 spring season. On the other hand, picloramplus 2,4-D at the last growth stage reduced yield 39% in 2002 but did not affect yield in 2003. We suggest that an excess of precipitation after application and above-normal air temperatures during grain fill may have increased crop injury with herbicides applied at the last growth stage. In short, the effect of different DE-750 mixtures with metsulfuron or 2,4-D on wheat yield could be the result of the interactions among environmental conditions, and application timing.
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