Leptochloa fusca (sprangletop).

Leptochloa fusca is a perennial weed with a global distribution. It is an aggressive species showing a competitive advantage in many situations due to its tolerance of saline and alkaline soils and its likely ability to fix nitrogen. It is commonly a serious weed of rice in many countries. It is recorded as invasive in Cuba, Hawaii and in the Chagos Archipelago (as L. fusca subsp. uninervia) and has been the subject of an 'eradication action' in Europe.

Predation on weed seeds and seedlings by Pheretima guillelmi and its potential for weed biocontrol

The soil weed seedbank is the source of future weed infestations. Seed predation can result in a large number of seed losses, thus contributing to weed biocontrol. Earthworms are important predators of seeds and seedlings and affect seeds and seedling survival after gut passage. A study was conducted to assess the ability of Pheretima guillelmi (Kinberg) to ingest and digest the seeds and seedlings of 15 main farmland weed species. Pheretima guillelmi ingested the seeds and seedlings of each weed species tested. The percentages of seeds and seedlings ingested were 96.7% to 100% and 21.7% to 94.2%, respectively. Pheretima guillelmi showed greater ingestion of seeds than seedlings for each species and digested the seeds and seedlings of each weed species tested to varying extents. The percentages of seeds and seedlings digested were less than 15% irrespective of the weed species. Passage through the gut of P. guillelmi affected the survival of seeds and seedlings. The germination of large crabgrass [Digitaria sanguinalis (L.) Scop.], green foxtail [Setaria viridis (L.) P. Beauv.], goosegrass [Eleusine indica (L.) Gaertn.], Chinese sprangletop [Leptochloa chinensis (L.) Nees], Malabar sprangletop [Leptochloa fusca (L.) Kunth], redroot pigweed (Amaranthus retroflexus L.), common purslane (Portulaca oleracea L.), barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.], and ricefield flatsedge (Cyperus iria L.) seeds egested by P. guillelmi decreased by 46%, 49%, 47%, 25%, 38%, 26%, 32%, 13%, and 15%, respectively, compared with their respective controls. In contrast to seed ingestion, ingestion of seedlings by P. guillelmi was fatal to individuals of all weed species; no seedlings survived passage through the gut. Our results indicate that predation of weed seeds and seedlings by P. guillelmi probably depletes the soil weed seedbank and that the introduction of P. guillelmi into fields is a potential strategy for weed biocontrol in farmland.

Survey of bearded sprangletop (Leptochloa fusca spp. fasicularis) response to clomazone in California rice

Bearded sprangletop is a problematic weed in California rice production and few herbicides provide effective control. As control of bearded sprangletop has declined, grower suspicion of resistance to clomazone has increased, because of the continuous rice cropping system and herbicide dependence in the region. The objectives of this research were to confirm clomazone resistance in bearded sprangletop populations and determine the level of resistance. Seed from 21 suspected clomazone-resistant populations was collected from the California rice growing region. A greenhouse experiment was conducted to determine population sensitivity to clomazone. Clomazone was applied into the water to emerging seedlings. Plant ht and control of bearded sprangletop were recorded weekly for 3 wk, plants were then harvested, and dry weight was measured. Of the populations tested, 17 were susceptible and four (5%) were resistant to clomazone. A dose-response assay was conducted using eight doses ranging from an eighth of the full rate to 12 times the full rate. The three most resistant populations had resistant-to susceptible ratios of 1.25×, 2×, and 5× the labeled rate of clomazone. The use of clomazone in California rice production is beneficial; however, it should be used at the appropriate timing and as part of an herbicide program to prevent further development of clomazone resistance.

Unveiling the Potential of Novel Macrophytes for the Treatment of Tannery Effluent in Vertical Flow Pilot Constructed Wetlands

The phytoremediation potential of macrophytic species has made them an inevitable component of constructed wetlands (CWs) for the treatment of industrial effluents. The macrophytes must have tolerance for the harsh conditions imposed by effluents for an effective establishment of the CW system. In this context, the basic purpose of this work was to investigate the efficacy of five indigenous emergent macrophytes (Brachiaria mutica, Canna indica, Cyperus laevigatus, Leptochloa fusca, and Typha domingensis) for the remediation of tannery effluent in vertical subsurface flow CWs. The ability of each macrophytic species to tolerate pollution load and to remove pollutants from the effluent was assessed. The effect of tannery effluent on the survival and growth of macrophytes was also studied. The treated tannery effluent samples were analyzed for electrical conductivity (EC), pH, biochemical oxygen demand (BOD5), chemical oxygen demand (COD), total dissolved solids (TDS), total suspended solids (TSS), chlorides (Cl−), sulphates (SO42−), oil and grease, and Cr levels. All of the studied macrophytes significantly decreased the pollution load of tannery effluent, and the higher nutrient content of effluent stimulated their growth without any signs of negative health effects. Leptochloa fusca and T. domingensis performed better in removing pollutants and showed higher growth rates and biomass than other tested macrophytes and can be considered preferred species for use in CWs treating tannery effluent. Brachiaria mutica showed morphologically better results than C. indica and C. laevigatus.

Remediation of polluted river water by floating treatment wetlands

In this study, the potential of floating treatment wetlands (FTWs), inoculated with selected bacteria, to ameliorate polluted river water was evaluated. Floating cells were prepared by vegetating plants, Typha domingensis and Leptochloa fusca, on a floating mat. The plants were inoculated with three different pollutant-degrading rhizospheric and endophytic bacterial strains. Significantly greater decrease in chemical oxygen demand (COD), biochemical oxygen demand (BOD5) and total organic carbon (TOC) was observed in inoculated FTWs than in the wetlands without bacterial inoculation. However, a slight decrease in pH and EC was seen in most of the treatments. The total nitrogen (TN), nitrate and total phosphorus (TP) contents decreased to 1.77 mg/L, 0.80 mg/L and 0.60 mg/L, respectively. Additionally, the concentration of iron (Fe), nickel (Ni), manganese (Mn), lead (Pb), and chromium (Cr) in the water lowered to 0.41, 0.16, 0.10, 0.25, and 0.08 mg/L, respectively. Overall the performance of T. domingensis was significantly better than L. fusca. The treated effluents meet the water quality guidelines for irrigation and aquatic life. This study revealed that FTWs supplemented with selective bacteria are a promising approach for the restoration and management of polluted river water.