Characterization and alleviation of the influence of moisture stress on fenoxaprop efficacy

A multi-faceted approach was implemented to characterize and alleviate the influence of moisture stress on fenoxaprop efficacy. Methods were adapted to investigate the influence of moisture stress level and duration on the efficacy and metabolic fate of fenoxaprop. Additionally, field research was conducted to determine methods for alleviating the reduced efficacy associated with moisture stress.; Moisture stress methodology utilized a semipermeable membrane system which separated the soil from solutions containing several concentrations of polyethylene glycol (PEG). Linear relationships existed between predawn plant water potential ({dollar}Psi{dollar}), soil matric ({dollar}Psi{dollar}m), and PEG solution osmotic potential ({dollar}Psipi{dollar}). Crabgrass shoot dry weight was linearly reduced by decreasing soil {dollar}Psi{dollar}m to {dollar}-{dollar}0.8 MPa, where no visible growth occurred.; Specific soil {dollar}Psi{dollar}m levels tested were {dollar}-{dollar}0.01 (field capacity), {dollar}-{dollar}0.2, {dollar}-{dollar}0.4, {dollar}-{dollar}0.8, {dollar}-{dollar}1.0 MPa using the PEG membrane system. Soil {dollar}Psi{dollar}m at or below {dollar}-{dollar}0.8 MPa significantly reduced fenoxaprop efficacy, independent of herbicide rate and moisture stress duration. Field lysimeter results indicated, that under moisture stress conditions shoot dry weight was reduced by 65 to 94% with tank mix combinations of {dollar}geq{dollar}0.27 kg ha{dollar}sp{lcub}-1{rcub}{dollar} fenoxaprop and {dollar}geq{dollar}2.2 kg ha{dollar}sp{lcub}-1{rcub}{dollar} pendimethalin. These rate combinations were shown to be synergistic and could alleviate the reduced efficacy of fenoxaprop associated with moisture stress.; Laboratory experiments demonstrated that fenoxaprop spray retention decreased linearly to 20% with decreasing soil {dollar}Psi{dollar}m to {dollar}-{dollar}0.8 MPa. Absorption and translocation of {dollar}sp{lcub}14{rcub}{dollar}C-fenoxaprop were not affected by moisture stress. The concentration of fenoxaprop-ethyl in the treated leaf was 5 to 10% greater and fenoxaprop acid content 7 to 10% less at soil {dollar}Psi{dollar}m {dollar}-{dollar}0.4 MPa when returned to {dollar}-{dollar}0.01 MPa at 96 h. These results suggest that slight alterations in fenoxaprop retention, and metabolism of fenoxaprop-ethyl are consistent with the reduced activity observed in the PEG study.; Based on these results, irrigation scheduling and tank mixing with pendimethalin should enhance the consistency of fenoxaprop on the control of moisture-stressed crabgrass.