Physiological and ecological characteristics of sugarcane field weeds in the Ryukyu Islands. 9. Effect of shade on growth and seed production of Rottboellia exaltata L.f. and Solanum alatum Moench.

Field studies were conducted with Rottboellia exaltata L. f. and Solanum alatum MOENCH., large annual weed species abundant in sugarcane fields, under shade intensities of 0, 22, 37, 65 and 94% to determine the effect of shade on the growth and seed production of these plants.1. Plant height increased under 22-37% shade and was inhibited greatly under 94% shade. Plant length increased under 37-65% shade and was inhibited greatly under 94% shade. There was no marked difference in plant height between the 65% plot and the control plot. Plant length was less affected by shading than plant height (Fig. 1).2. Number of tillers per plant and number of branches per plant decreased with increasing shade intensity and were inhibited the most under 94% shade. At this intensity, no tillers and virtually no branches were produced (Fig. 2.).3. Leaf area decreased with increasing shade intensity, and Rottboellia was more affected by shading than Solanum (Fig. 3.).4. Total dry weight decreased with increasing shade intensity and under 94% shade was less than 1.4% of the control in Rottboellia and less than 2.1% of the control in Rottboellia. Spike weight and fruit weight decreased at a fast rate, especially under 37% shade (Fig. 4.).5. Heading and flowering were delayed as the shade intensity was increased. Rottboellia was less affected by shading than Solanum. Spike number, spike length, spike weight, fruit number and fruit weight tended to decrease as shade intensity was decreased and no fruits were produced under 94% shade (Table 1.).6. The amount of shade required to control the weeds appears to be above 94%.