The influence of post‐emergence weed harrowing on selectivity, crop recovery and crop yield in different growth stages of winter wheat

Crop tolerance and weed control in winter wheat were investigated to evaluate the influence of post-emergence weed harrowing at different crop growth stages on selectivity, crop recovery and crop yield. The importance of growth stage was investigated in autumn (Denmark) and spring (Germany). Selectivity was chosen as a measure of the relationship between weed control and crop soil cover, with crop recovery as a measure of how crop yield was affected by soil cover in the absence of weeds. Selectivity was unaffected by crop growth stage in autumn and spring. In autumn, 80% weed control was associated with 6% crop soil cover, whereas in spring, 80% weed control corresponded to 26% crop soil cover. Crop recovery was higher in late growth stages in autumn and spring. With 25% crop soil cover, crop yield losses occurred in the ranges of 1–4% in autumn and 0.3–0.8% in spring. Weed control experiments revealed that the maximum crop yield response to harrowing was comparable with herbicide treatment. The average yield gain was 13% in autumn (Denmark) and 27% in spring (Germany). This study contributes parameter estimates that can be used in future models to evaluate optimum harrowing intensity.

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