Weeds are the main constraint in the adoption of zero-till, dry-seeded rice systems because weeds and rice emerge simultaneously in these systems, and there is no standing water at crop establishment to suppress weeds. A study was conducted during the wet season of 2011 and the dry season of 2012 at the International Rice Research Institute to evaluate the performance of different herbicides in mechanized-sown, zero-till dry-seeded rice. Among the treatments evaluated, oxadiazon followed by penoxsulam + cyhalofop followed by one hand-weeding at 42 d after sowing, provided 23 to 35% higher yield than the nontreated control. The yields in the oxadiazon-treated plots were similar to those in the weed-free plots. Some weed species, including eclipta and doveweed, were not controlled by the evaluated herbicides. Therefore, there is a need to evaluate additional herbicides and to integrate them with cultural weed management strategies to manage such problematic weeds.

Experiments were conducted to determine the influence of various environmental factors on seed germination and seedling emergence of eclipta. Seed germination was completely inhibited in the dark, whereas in the light/dark it was 76, 93, and 87% at 25/15, 30/20, and 35/25 C alternating day/night temperatures, respectively. Germination was greater than 80% up to a temperature of 140 C, when seed were placed in an oven for 5 min followed by incubation at 30/20 C for 14 d, but declined progressively with a further increase in exposure temperature with no germination at 200 C. Seed germination was tolerant of salt stress but highly sensitive to water stress. Seed germinated (87 to 93%) over a pH range of 4 to 10. Seedling emergence was greatest (83%) for the seed placed on the soil surface but declined thereafter, and no seedlings emerged from a depth of 0.5 cm. Seedling emergence was slower and lower with the addition of 4 to 6 t ha−1 of plant residue. The information gained from this study identifies some of the factors facilitating eclipta becoming a widespread weed in the humid tropics and might contribute to its control.