Jhoana Opeña

Weed management is a persistent challenge in Southeast Asian rice production, particularly in direct-seeded rice (DSR), due to the diversity of weed species and variable field and environmental conditions that can compromise weed control, necessitating innovative solutions. An integrated weed seed impact mill (iWSIM) reduces weed seed banks by destroying weed seeds during the harvest process. This mixed study is the first to fully explore the applicability of iWSIM technology in Southeast Asian rice systems, focusing on both combine harvester and iWSIM specifications and operation, determinants of efficacy, and field and harvest conditions. Weed seed bank reduction with an iWSIM depends on several factors, including weed seed retention and subsequent capture by the combine at harvest, weed seed separation into the chaff fraction, and the iWSIM’s efficacy against weed seeds captured in the chaff fraction. Observations from Southeast Asia indicate variable seed retention among key weed species, presenting challenges for harvesting strategies and iWSIM effectiveness. To optimize the iWSIM efficacy, recommendations include larger fields to reduce the weed seed produced on bunds, achieving complete early-season weed control, lowering the harvest header height to about 15 cm to capture more weed seeds, cleaning mechanism adjustments to ensure weed seeds are retained in the chaff fraction, and greater combine harvester engine power to allow a lower header height and power the iWSIM. The estimated weed control benefits of the iWSIM should also be weighed against additional equipment operating costs. iWSIM technology holds promise as part of a sustainable solution for weed control in Southeast Asian rice, contingent upon further region-specific research and adaptation.

This study was conducted in the laboratory and screenhouse to determine the effects of temperature, light, osmotic stress, salt stress, burial depth, use of crop residues as mulch, depth of flooding, and use of POST herbicides on the emergence, survival, and growth of doveweed. In the light/dark regime, germination was higher at alternating day/night temperatures of 35/25 C (95%) than at 30/20 C (72%), and no germination occurred at 25/15 C. Light strongly influenced germination (95%) and dark completely inhibited germination. No germination occurred at an osmotic potential of −0.8 MPa and a salt concentration of 150 mM and above. The highest germination (91%) was observed from the seeds sown on the soil surface and emergence decreased by 78, 86, and 92% when burial depths were increased to 0.5, 1, and 2 cm, respectively. No seedlings emerged from seeds buried at depths of more than 2 cm. The use of rice residues as mulch significantly reduced the emergence and growth of doveweed seedlings. The amount of residue required to suppress 50% of the maximum biomass was 2.5 t ha⁻¹. Flooding had a more pronounced effect on seedling biomass than seedling emergence. Biomass was reduced by 78, 92, and 96% when flooding depths increased from 0 to 2, 4, and 6 cm, respectively, for the seeds placed on the soil surface, whereas for the seeds buried at 0.5 cm, these values were 78, 100, and 100%. Bentazon (100 g ha⁻¹) and bispyribac-sodium (30 g ha⁻¹) provided 100% control of doveweed when applied at the three-leaf stage. Doveweed control was less than 31% with glyphosate rates up to 2,000 g ha⁻¹. The application of 2,4-D (500 g ha⁻¹) provided 100% control of doveweed even when applied at the seven-leaf stage. The information from this study could help in developing more sustainable and effective integrated weed management strategies for the control of this weed and weeds with similar response in dry-seeded rice systems.

Echinochloa glabrescens is a C₄ grass weed that is very competitive with rice when left uncontrolled. The competitive ability of weeds is intensified in direct-seeded rice production systems. A better understanding is needed of factors affecting weed seed germination, which can be used as a component of integrated weed management in direct-seeded rice. This study was conducted to determine the effects of temperature, light, salt and osmotic stress, burial depth, crop residue, time and depth of flooding, and herbicide application on the emergence, survival, and growth of two populations [Nueva Ecija (NE) and Los Baños (IR)] of E. glabrescens. Seeds from both populations germinated at all temperatures. The NE population had a higher germination rate (88%) from light stimulation than did the IR population (34%). The salt concentration and osmotic potential required to inhibit 50% of germination were 313 mM and −0.24 MPa, respectively, for the NE population and 254 mM and −0.33 MPa, respectively, for the IR population. Emergence in the NE population was totally inhibited at 4-cm burial depth in the soil, whereas that of the IR population was inhibited at 8 cm. Compared with zero residue, the addition of 5 t ha⁻¹ of rice residue reduced emergence in the NE and IR populations by 38% and 9%, respectively. Early flooding (within 2 days after sowing) at 2-cm depth reduced shoot growth by 50% compared with non-flooded conditions. Pretilachlor applied at 0.075 kg ai ha⁻¹ followed by shallow flooding (2-cm depth) reduced seedling emergence by 94−96% compared with the nontreated flooded treatment. Application of postemergence herbicides at 4-leaf stage provided 85−100% control in both populations. Results suggest that integration of different strategies may enable sustainable management of this weed and of weeds with similar germination responses.

The biology of purple nutsedge was studied by growing it alone and in competition with 12 and 24 rice plants in a pot experiment. Compared with the weedy plants grown alone, competition from rice reduced purple nutsedge leaf number, shoot number, tuber production rate, and leaf biomass. At 10 wk after planting, interference from 12 and 24 rice plants reduced purple nutsedge leaf area by 79 and 86%, respectively, compared with weedy plants grown without rice interference. On the same date, purple nutsedge aboveground shoot biomass was 26.8 g plant⁻¹without interference, whereas in interference with 12 and 24 rice plants, purple nutsedge produced aboveground biomass of 4.8 and 2.2 g plant⁻¹, respectively. A total of 95 tubers plant⁻¹were produced by purple nutsedge when grown alone. Growth with 12 and 24 rice plants reduced tuber production to 33 and 17 tubers plant⁻¹, respectively. Without interference, purple nutsedge produced 40 g plant⁻¹of total biomass of tuber plus root plus rhizome, whereas in interference with 12 and 24 rice plants, purple nutsedge produced 14 and 5 g plant⁻¹of total belowground biomass, respectively.