MCPA Synergizes Imazamox Control of Feral Rye (Secale cereale)

Abstract

Field, greenhouse, and laboratory studies were conducted to determine the effect of MCPA ester, fertilizer type, and fertilizer rate on feral rye control with imazamox. In field studies near Sidney, NE, increasing the concentration of liquid ammonium phosphate (10–34–0) from 2.5 to 50% of the spray solution decreased feral rye control with imazamox by as much as 73%. Conversely, adding MCPA ester to imazamox significantly increased feral rye control in field studies by up to 77%. Initial greenhouse studies confirmed the liquid ammonium phosphate antagonism effect, but subsequent greenhouse studies were inconsistent with regard to the interaction between fertilizer and imazamox. At least one source of liquid ammonium phosphate was shown not to be antagonistic, and therefore fertilizer source or contaminants may be responsible for initial field observations. Greenhouse studies confirmed the synergistic interaction between MCPA and imazamox. MCPA ester applied at 560 g ai ha−1 decreased the rate of imazamox required to cause 50% reduction in feral rye dry weight (GR50) to 13 g ha−1 compared to 35 g ha−1 for imazamox alone. Although addition of MCPA ester increased 14C-imazamox absorption by 8% in laboratory studies, less 14C translocated out of the treated leaf; therefore the mechanism of synergism does not appear to be related to imazamox absorption or translocation.

Uptake, translocation and metabolism of aminocyclopyrachlor in prickly lettuce, rush skeletonweed and yellow starthistle

“…Absorption data were fit to an asymptotic, exponential, maximum‐two‐term model as the following equation: where y is the percentage absorption expressed as a percentage of the applied dose, a is the upper asymptote, or theoretical absorption maximum, x is time, expressed as hours after treatment, and b is a slope term that has a positive relationship to the rate with which absorption reaches maximal levels. Identical regression analysis has been used to model absorption of imazamox in feral rye to understand MCPA‐ester/imazamox synergism 33…”

Nonlinear Regression Analysis of Herbicide Absorption Studies

“…For example, the AR model was far more likely to be the better model for the Kniss (2006) data set compared with the RHB model based on AICc, and the AR model provided A max estimates of 69 to 73%, which were very similar to the maximum absorption observed in that study (67 to 70%); conversely, the RHB model provided A max estimates of 91 to 96%, far greater than any absorption value that was observed in the study. Similarly, the RHB model provided a better description of the Kniss et al (2011) data set, and the A max estimates were more similar to the observed maximum absorption values for each treatment compared with the AR model.…”

“…To determine which model best describes foliar herbicide absorption, 10 herbicideabsorption data sets were analyzed using the AR model (Equation 4) and the RHB model (Equation 9). Raw data were used for four of the data sets (Bukun et al 2009(Bukun et al , 2010Kniss 2006;Kniss et al 2011). For the remaining 6 data sets, treatment means reported in the published articles were used (Everman et al 2009a,b;Frihauf et al 2010;Hennigh and Al-Khatib 2010;Schuster et al 2007;Weinberg et al 2007).…”

“…At this cutoff value, there was sufficient evidence to choose one model over the other for the remaining five data sets. Of these five data sets, the RHB model was selected as the better model in four cases (Frihauf et al 2010;Hennigh and Al-Khatib 2010;Kniss et al 2011;Weinberg et al 2007), whereas the AR model was selected in one case (Kniss 2006). Based on these results, there is not sufficient evidence that one of these models provides a better description of foliar herbicide absorption in general.…”

“…Saflufenacil applied alone to winter wheat exhibited self-limiting effects with respect to absorption, whereas the safening effect of 2,4-D allowed more saflufenacil to enter the plant. In this case, much of this effect would have been missed if the time points had ranged only from 0 to 24 h. Kniss et al (2011) used a much shorter range of time points than did Bukun et al (2009Bukun et al ( , 2010 and Frihauf et al (2010) to evaluate the effect of MCPA ester and spray additives on imazamox absorption in feral rye (Secale cereale L.) ( Figure 2D). In this study, the shorter period was appropriate because the t 90 values were estimated to be , 23 h for all treatments.…”