Effects of crop canopy structure on herbicide deposition and performance

P>To explore the relationship between canopy structure of winter wheat and herbicide performance, new indices representing canopy structural characteristics have been devised. Canopy structures of six different wheat cultivars grown in trays were determined and herbicide deposition and performance measured in a split-plot experiment. A canopy index (Cp) was devised as the ratio of growing canopy height to manually extended maximum plant height, as a representation of structure and stem and leaf inclination. Canopy volume was taken as the volume within the canopy consisting of one main stem and two tillers. Canopy index and volume were closely correlated with individual crop growth characteristics. These indices were also closely correlated with each other (r = 0.80; P < 0.001) and showed relatively consistent correlation with other characteristics, such as leaf area, plant height, canopy area, and light penetration as the wheat grew. Canopy index and volume were closely but negatively correlated with light penetration (r = -0.87; P < 0.001 and -0.71; P < 0.001 respectively), which in turn showed close correlation with herbicide deposition. The amount of herbicide deposition on the soil surface was positively correlated with weed biomass. Surprisingly, the amount on target weeds was uncorrelated with final weed biomass, indicating that herbicide performance was not dependent upon deposition on the target in different crop cultivars with different canopy structures. Our findings thus demonstrate the importance of crop canopy structure, represented by canopy index and volume, in herbicide performance. These new indices should be useful for investigating crop canopy structure in relation to crop competitivity and herbicide performance.