Allelopathic Effect of Zea mays, Senna spectabilis and Muntingia calabura on Weeds: Potential Implication for Controlling Weeds in Tea Lands

Abstract

Identification of eco-friendly weed control measures is imperative due to the adverse effects of excessive use of synthetic herbicides. Thus, a series of bioassays and field studies were conducted to evaluate the allelopathic potential of three plant spp., namely, Maize (Zea mays), Kaha-kona (Senna spectabilis) and Jam (Muntingia calabura) in tea lands. The specific objectives were to identify the most phytotoxic extract, its effective concentration and effective extraction method, synergistic/antagonistic effects, allelochemical releasing mode and field efficacy to control weeds. Plant extracts for bioassays were prepared with dry powders of leaves/husk in four concentrations (4, 6, 8 and 10% w/v) using hot and cold distilled water. Synergistic/antagonistic effects were tested using cocktails of different extracts mixed at different ratios. Allelochemical releasing mode (decomposition, volatilization and leaching) was identified by pot bioassay, dish pack and sandwich methods, respectively. These treatments were evaluated on lettuce as an indicator plant. Meanwhile, the three most allelopathic extracts/materials were tested in the field by spraying/mulching. Results revealed no significant difference among hot and cold-water extraction (p>0.05). 10% concentration showed the highest phytotoxicity (lowest germination of lettuce). Jam and Kaha-kona showed the highest phytotoxicity evidenced by the lowest germination (22-23%), followed by Maize (44%). Germination was inhibited at 100% in all cocktails indicating their synergistic effect. Leaching was prominent in Kaha-kona evidenced by the lowest germination (61%) and the highest inhibitory effect on radical (77%) and hypocotyl (71%) elongation. Volatilization was prominent in Kaha-kona and Jam while decomposition was notable in Maize (leaves) and Kaha-kona. Mulching was effective compared to spraying (10%, 450 ml m-2), where maize mulching recorded the lowest weed emergence, followed by Jam (77-84% weed dry weight reduction). In conclusion, S. spectabilis and M.calabura demonstrate high allelopathic potential, followed by Z. mays highlighting its potential implication for eco-friendly weed control. Further investigations are needed to evaluate the field efficacy of these botanicals in controlling different weed species.