Allelopathic Potential of Aqueous Extracts of Wild Sunflower (Tithonia diversifolia (Hemsl.) A. Gray) and Sorghum (Sorghum bicolor (L.) Moench) for Controling Weeds and Enhancing Yield of Cowpea (Vigna unguiculata (L.) Walp)

Cowpea is an important grain legume in Sri Lanka. Approximately 53–60% of yield losses in cowpea cultivation are attributed to weeds. Chemical weed control (herbicide), is one of the method in weed control in cowpea. Import of herbicide have been prohibited recently since of government policy and the nation's economic problems. As a result, it's critical to identify other suitable alternatives. In this context, a field experiment was conducted to study the effect of aqueous extract of wild sunflower and sorghum on weed control, growth and yield of cowpea. The experiment consisting of five weed control treatments viz T1 (aqueous extract of wild sunflower; 12 L ha-1 ,T2 (aqueous extract of sorghum; 12 L ha-1), T3 (combined application of both wild sunflower and sorghum aqueous extract in a 1:1 ratio; 6+6 L ha-1), T4 (hand weeding), and T5 (unweeded check-control) was conducted in Randomized Complete Block Design with four replication in the crop farm of Eastern University, Sri Lanka.. The experiment was conducted from September to November 2022. Hand weeding was done on 21 and 42 DAS while application of aqueous extracts were done on 2, 21, and 35 DAS. Minitab 17 software was used for the statistical analysis, and Tukey's test was used to compare the treatment means. The results revealed that the different weed control treatments had a substantial (P<0.05) impact on weed population & dry weight, growth and yield of cowpea. When compared to the control, hand weeding was found to be most effective to control weeds followed by combined application of aqueous extracts from wild sunflower and sorghum Hand weeding and the combined application of aqueous extracts significantly reduced the number of weeds by 82.98 and 54.39%, respectively. Further, the hand weeding and combined application of extract significantly enhanced yield by 45.09% and 62.85% respectively in comparison to the control (unweeded check). According to the study's findings, it can be concluded that under the condition of Sri Lanka, combined application of aqueous extracts was proved to be more remunerative and sustainable alternate option for weed control in cowpea crop.