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.
