Effect Spraying Volume of Cosmos sulphureus Cav. Flower Extract on Weed Dominance and Soybean Yield

Allelochemical based herbicides are environmentally friendly management alternatives. Thus, cosmos (Cosmos sulphureus Cav.) flower extract as a bioherbicide was investigated in soybean productions. This study aimed to determine effective spraying volume of C. sulphureus flower extract to manage weeds based on weed dominances and soybean yield. This research was conducted at Banguntapan Village, Bantul District, Special Region of Yogyakarta Province, Indonesia on August to November 2018. This study was set as a single factor Randomized Complete Block Design (RCBD) with three replications set as blocks. Three spraying volumes; 1000, 2000, 3000 L.ha-1 and two weed management practices were used as control. Continued weed free and weeded treatments were used to determine soybean yield lost. Data were analyzed using Analysis of Variance (ANOVA), continued with Least Significant Differences (LSD) at the 0.05 probability level. Results showed weed species in soybean fields was dominated by purple nutsedge (Cyperus rotundus L.). The 400 g.L-1 extract concentration applied at 3000 L.ha-1 resulted in similar weed control and soybean yield compared to pre-emergence herbicide application and manual weeding at 1 and 3 weeks after planting (WAP). These findings showed that extract of cosmos flowers possess bioherbicidal activity against weed without having detrimental effects on the soybean plants.