Abstract:
Impact of weed control methods on the persistence of Parthenium hysterophorus L., and tomato (Solanum lycopersicum L.) yield was studied in two farmer fields i.e. a site heavily infested with P. hysterophorus (Parthenium-site) and Parthenium free site, in the Jaffna peninsula of the Northern Province of Sri Lanka. The split-plot design consisted of two main plots i.e. manual weeding and ploughing (both followed by harrowing), and three sub-plots i.e. use of a pre-emergent herbicide (Oxyfluorfen; 240 g/L EC at 2 days before planting), mulching [Gliricidia sepium (Jacq.) Kunth ex Walp. leaves at 12 kg per plot on fresh weight basis], and un-weeded plot after crop establishment (control), in three replicates. The soil seed bank of the Parthenium-site was dominated by P.hysterophorus as expected, and the Parthenium-free site was dominated by the perennial sedge Cyperus rotundus L. At tomato harvest, the un-weeded sub-plots recorded the highest weed densities (p<0.05) when compared to the rest, The Parthenium-site showed a higher weed dry weight (p<0.05) when compared to that of the Parthenium-free site, due to higher emergence of the Parthenium weed in the former. Mulching was the best sub-plot treatment for Parthenium control in combination with the main plot treatments. The average fruit weight of tomato at the Parthenium-free site was 7.8 % higher than that of the Parthenium site (47.8 g per fruit). In the Parthenium-site, mulching resulted in a 6.4% higher fruit weight and 58% higher total yield (p<0.05) when compared to the rest of the sub-plot treatments. The weed competition negatively affected the tomato yield (Y=-0.7551X+7.88; R2=0.58; p<0.05), with Parthenium weed playing a dominant role. Mulching with G. sepium coupled with manual weeding during land preparation or ploughing would suppress growth and development of weeds including P. hysterophorus and enhance yield of tomato.
