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.
Highlights
Since the 1980s, many Asian farmers have shifted from transplanting to direct-seeding methods of crop establishment [1]
Preliminary seed germination and seedling emergence tests The I. rugosum seeds used in this study came from two population sources, one population labeled as SC from the screenhouse, and another other labeled as UI from the International Rice Reseach Institute (IRRI) upland fields
Cultural management practices such as seed burial through shallow tillage and the use of rice residue as mulch can significantly suppress seedling emergence and growth, when residue mulching is done in combination with pre-emergence herbicide application
Summary
Since the 1980s, many Asian farmers have shifted from transplanting to direct-seeding methods of crop establishment [1]. The risk for yield loss caused by weeds is higher in direct-seeded rice due to the absence of standing water during crop emergence and the lack of seedling size advantage of rice over weeds [5]. Once established in the field, I. rugosum is difficult to control by chemical or mechanical means [8]. This weed resembles the rice (Oryza sativa L.) plant, making it difficult to distinguish [9]. It is considered as one of the noxious weeds by the United States Department of Agriculture (USDA) [10]
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