title: Influence of Environmental Factors, Cultural Practices, and Herbicide Application on Seed Germination and Emergence Ecology of Ischaemum rugosum Salisb.
abstract: Ischaemum rugosum Salisb. (Saramolla grass) is a noxious weed of rice that is difficult to control by chemical or mechanical means once established. A study was conducted to determine the effect of light, temperature, salt, drought, flooding, rice residue mulch, burial depth, and pre-emergence herbicides on seed germination and emergence of I. rugosum. Germination was stimulated by light and inhibited under complete darkness. Optimum temperature for germination was 30/20°C (97.5% germination). Germination reduced from 31 to 3.5% when the osmotic potential of the growing medium decreased from -0.1 to -0.6 MPa and no germination occurred at -0.8 MPa. Germination was 18 and 0.5% at 50 and 100 mM NaCl concentrations, respectively, but was completely inhibited at 150 mM or higher. Residue application at 1-6 t ha-1 reduced weed emergence by 35-88% and shoot biomass by 55-95%. The efficacy of pre-emergence herbicides increased with increasing application rates and decreased with increasing rice residue mulching. The efficacy of herbicides was in the order of oxadiazon> pendimethalin> pretilachlor. At 6 t ha-1, all herbicides, regardless of rates, did not differ from the control treatment. I. rugosum seeds buried at 2 cm or deeper did not emerge; however, they emerged by 4.5 and 0.5% at 0.5 and 1 cm depths, respectively, compared to the 39% germination for soil surface seeding. Flooding at 4 DAS or earlier reduced seedling emergence and shoot biomass while flooding at 8 DAS reduced only seedling emergence. The depth and timing of flooding independently reduced root biomass. Flooding at 4 and 6 cm depths reduced the root biomass. Relative to flooding on the day of sowing, flooding at 8 DAS increased root biomass by 89%. Similarly, flooding on the day of sowing and at 2 DAS reduced the root-shoot biomass ratio. Under the no-flood treatment, increasing rates of pretilachlor from 0.075 to 0.3 kg ai ha-1 reduced weed emergence by 61-79%. At the flooding depth of 2-4 cm, pretilachlor reduced weed emergence and shoot and root biomass, but the differences across rates were non-significant. Information generated in this study will be helpful in developing integrated weed management strategies for managing this weed.
authors.affiliation: Weed Science, Crop and Environmental Sciences Division, International Rice Research Institute (IRRI), Los Baños, Philippines; Crop Science Cluster, College of Agriculture, University of Philippines, Los Baños, Phillipines.
authors.forename: Charlemagne Alexander A
authors.initials: CA
authors.lastname: Lim
authors.affiliation: Weed Science, Crop and Environmental Sciences Division, International Rice Research Institute (IRRI), Los Baños, Philippines; Crop Science Cluster, College of Agriculture, University of Philippines, Los Baños, Phillipines.
authors.forename: Tahir Hussain
authors.initials: TH
authors.lastname: Awan
authors.affiliation: Crop Science Cluster, College of Agriculture, University of Philippines, Los Baños, Phillipines.
authors.forename: Pompe C
authors.initials: PC
authors.lastname: Sta Cruz
authors.affiliation: The Queensland Alliance for Agriculture and Food Innovation, The University of Queensland, Toowoomba, Queensland, Australia.
authors.forename: Bhagirath Singh
authors.initials: BS
authors.lastname: Chauhan
mesh_terms: D018556:Crops, Agricultural / Q000502:physiology; D004777:Environment; D018525:Germination / Q000187:drug effects*; D006540:Herbicides / Q000633:toxicity*; D008027:Light; D006109:Poaceae / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D054712:Salinity; D036226:Seedlings / Q000187:drug effects* / Q000502:physiology; D013696:Temperature; D058728:Weed Control / Q000379:methods
chemical_list: D006540:Herbicides