3.1 Shade avoidance cues at sugar beet emergence and the duration of shade avoidance cues added later affected sugar beet growth and development
When the shade avoidance cue was present at sugar beet emergence (early-season removal series), the effect of the weed-free indicator variable (P = 0.065) and the linear effect of weed duration (P < 0.001) impacted sugar beet leaf number at harvest, suggesting a substantial drop in leaf number from the early season weed exposure, but continuing effects as the shade avoidance cue remained throughout the season (Table 2). However, reductions in sugar beet leaf area, leaf biomass and root biomass were attributable to the presence of weeds through the two true-leaf stage (P < 0.001). Once adjusted for the weed-free vs weedy treatment comparison, there was no effect of weedy duration in the early-season removal series (P > 0.42), suggesting the duration of weed presence beyond the 2 true-leaf stage had minimal effect. In contrast, when the shade avoidance cue was added after the sugar beet 2 true-leaf stage, duration of weed presence had a significant effect on sugar beet growth reduction.