Effects of Shading on Early Growth and Regrowth of Broadleaf Dock (Rumex obtusifolius L.) in Spring Sowing

Abstract

In order to obtain basic information for the control of broadleaf dock (Rumex obtusifolius L.), an aggressive weed in grasslands, experiments were conducted using 1/2000 a wagner pots at different shading intensities, control (no shading), 80, 90, 95 and 100% to determine the effects of shading starting at different growth stages (seed, cotyledon, 1st leaf, 3rd leaf and 5th leaf stages) on early growth and regrowth of this weed under spring sowing. Tops of all the plants were clipped on the day when non-shaded plants were at the full-bloom stage. These continued to grow without shading thereafter.
In the early phase of growth, emergence percentages at each shading intensity were high for the control and 100% shading treatments, and low for the 80-95% shading treatments (Table 1). Plant length, leaf number, leaf area and top dry weight (seed, leaf and stem weight) decreased with the increase of the shading intensity and when the shading treatments were initiated at early stages. Especially, the leaf area and top dry weight decreased remarkably under shading treatments as compared with the non shading treatments. Seed production was not observed except for the control and 80% and 90% shading treatments which were initiated from the 5th leaf stage (Fig. 1, 2, 3, 4).
For the regrowth, the sprouting percentage decreased with the increase of the shading intensity in all the plants regardless of the growth stages when the treatment was initiated (Table 2). The viability of the plants at harvest was almost 0 percent under 95% and 100% shding treatments irrespective of the growth stages when the shading treatment was initiated. The top and root (tap and lateral roots) dry weight decreased linearly with the increase of the shading intensities and when the shading treatments were initiated at earlier stages (Fig. 5).
These results suggest that the shading treatment exerts a highly inhibitory effect on the seedling growth of broadleaf dock. It was suggested that 90% shading treatments should be applied until the 1st leaf stage at the latest e. g. using quick growing grass species, for restricting the emergence and early growth of the seedlings of this weed at the time of spring renovation.