Allelopathic Effects of Chrysanthemoides monilifera subsp. monilifera on Lolium rigidum in Wheat Field: Implications on the Reduction of Chemical Loads in Agro-Ecosystems

Weed control through allelopathic plants is a promising approach that may minimize many of negative consequences of synthetic herbicides. We have studied potential of Chrysanthemoides monilifera subsp. monilifera (boneseed) leaf extract for controlling growth of Lolium rigidum (annual ryegrass) in wheat (Triticum aestivum) fields. Both pre-and post-emergent ryegrass-control experiments were conducted in greenhouse using field soil. Treatments such as boneseed leaf extracts (5 and 10% for pre-emergent and 10 and 20% for post-emergent experiments) alone or as a mixture combined with different strength (¼ and ½ strength) of pre-emergent (boxer gold) and post-emergent (hussar OD) herbicides were applied on pre- and post-emergent ryegrass and wheat. The findings revealed that none of the boneseed leaf extracts alone or as mixture had significant inhibitory impact on pre-emergent ryegrass compared with herbicide alone. Although we observed significant inhibitory impacts on post-emergent ryegrass with boneseed leaf extracts alone (10 and 20%) compared with control, they were negligible compared to full strength herbicides. Mixtures had significant inhibitory impact on post-emergent ryegrass compared with herbicide alone with same doses and impact increased with herbicide concentration. Despite the greater impacts by higher herbicides concentration alone, findings suggest the use of mixture of ¼-strength herbicide and 10% boneseed leaf extract was able to control ryegrass successfully than the herbicide alone without adverse impacts on wheat. This study suggests that use of boneseed leaf extract mixed with lower doses of post-emergent herbicides may be effective in controlling ryegrass with concomitant reductions in expenses and ecological health risks linked with the practice of synthetic herbicides.

2,4-D and dicamba removal from the surface of plastic mulch using overhead irrigation: analytical analysis and cucurbit bioassay crop response

Glyphosate and paraquat are effective preplant burndown herbicide options for multi-cropped vegetable production on plastic mulch, but problematic weeds such as wild radish, cutleaf eveningprimrose, annual morningglory, or horseweed may not be adequately controlled with these herbicides alone. 2,4-D and dicamba could help control these troublesome weeds prior to planting if they can be removed from plastic mulch for avoiding crop damage. Treatments included 2,4-D (1,065 and 2,130 g ae ha−1) and dicamba (560 and 1,120 g ae ha−1) applied broadcast over plastic mulch a day before transplanting. Just before transplanting, treatments received overhead irrigation at 0.76 cm or no irrigation. Plastic mulch samples were collected at application and planting to determine herbicide presence using analytical techniques, and cantaloupe and zucchini squash were subsequently transplanted on the plastic beds. Analytical UHPLC analysis determined 88-99% of the initial herbicide concentration was present at crop planting when irrigation was not implemented. At most, a 1/50 rate of dicamba and a 1/500 rate of 2,4-D was present at planting when overhead irrigation was applied prior to transplanting. Maximum cantaloupe and squash injury from 2,4-D with irrigation was 10% and did not influence plant growth, biomass, or yield. For dicamba with overhead irrigation, cantaloupe injury reached 35%, vine lengths were reduced 24% and maturity was delayed while squash injury ranged from 9 to 12% without influencing growth or yield. Without irrigation to wash herbicides from the mulch prior to planting, 60 to 100% injury of both crops occurred with both herbicides. Zucchini squash was more tolerant to dicamba compared to cantaloupe. Results demonstrated that 2,4-D can be adequately removed from the surface of plastic mulch with irrigation while a single irrigation event was not sufficient to remove dicamba.

Effect of four pre-planted cover crop species on weed control and population dynamics

The present research was conducted to assess the competition of four cover crop species including the Festuca ovina L., Festuca rubra L., Agropyron desertorum (Fischer ex Link) Shultes, and Bromus tomentellus Boiss with the weeds as well as enhancement of their establishment. B. tomentellus with 7.7 and 8.73 t h–1 had the highest dry weight production in 2016 and 2017, respectively. In 2016, the highest reduction in the dry weight of the weeds (73%) was observed for the F. ovina, at the rate of 600 g active ingredient per ha–1 of herbicide. In 2017, the highest reduction in the dry weight of the weeds (90%) was recorded at the rate of 600 g active ingredient per ha–1 of herbicide for the. Dry weight of the dominant weeds decreased by 70% approximately with the and at the rate of 600 g active ingredient per ha–1 of herbicide. Shannon Wiener index decreased in all the treatments following the increase in the herbicide concentrations in 2016 and 2017. The interaction of cover crop species and herbicide on the Margalef index was significant in all the treatments in 2016 except for A. desertorum, as well as A. desertorum and in 2017. Margalef index reduced following the increase in the herbicide concentration in all the treatments. Highlights - Bromus tomentellus Bioss and Festuca ovina L had the highest biomass production. - Bromus tomentellus (90%) and Festuca ovina (73%) treatments had the highest decrease in total weed dry weight compared to control. - The highest reduction in dry weight of total dominant weeds was influenced by B. tomentellus and Festuca ovina 73% and 83% at the rate of 600 g a.i. ha–1 of Bromocide M.A. EC respectively. - Margalof index reduced following the increase in herbicide concentration in all treatments. - Bromus tomentellus, Festuca ovina has the potential for reducing weeds in orchards and croplands.

Herbicides distribution in sediments of the Argentina rolling pampas landscape

<p>Soil losses due to water erosion exceed the tolerance in the edafoclimatic conditions of the rolling pampas. Erosion sediments transport pesticides outside their own limits. Increased knowledge about its polluting potential would allow agronomic practices to be redirected towards sustainability. The objectives of this work were to: a) analyze herbicide distribution patterns frequently used in agricultural production and b) evaluate some herbicide and soil properties to explain their landscape distribution pattern. In an area under exclusively agricultural production of the upper basin of Pergamino stream, rain simulations were carried out in different landscape positions (upland, mid slope, and lowland). In the upland and mid slope (well-drained Mollisols) agriculture is practiced with soybean monoculture tendency under no tillage; in the lowland (Mollisols and alkaline and saline Alfisols), cattle breeding and rearing is carried-out on improved grasslands. Sediments were obtained using a rain simulator for one hour at high intensity (60 mm h<sup>-1</sup>) at 23 sampling points. In the sediments, 2.4-D, acetochlor, atrazine and metabolites, flurochloridone, glyphosate and AMPA, and s-metolachlor concentrations were determined. In addition, the following variables: basic infiltration, runoff coefficient (%), slope, amount of sediments, texture, soil organic carbon (SOC), pH, electrical conductivity and exchangeable sodium at 0-5 cm were obtained. Non-parametric tests of herbicide concentrations between landscape positions and correlations with the analyzed variables were performed. The production systems practiced in the landscape different positions, even with low grade slopes, against heavy rains, favor surface runoff (between 45 and 64%) and generate significant sediment losses. No differences were found in the amount of sediment between landscape positions. There was also no relationship between sediment quantity and herbicide concentration. The herbicides applied in agriculture were moved to the lower parts of the landscape, where they are not applied. Three patterns of distribution of concentrations were found that corresponded to some herbicides and soils properties. The average concentrations of 2.4-D, acetochlor and s-metolachlor were higher in the lowland than in the upland and mid slope. The low/moderate adsorption coefficients, the moderate/high solubilities and their relationship with higher sand content and SOC led to their accumulation in the lowland. On the contrary, the average concentrations of glyphosate and AMPA were higher in the upland and mid slope positions, as a consequence of their high adsorption coefficient in soils with higher clay and silt content. Finally, the average concentrations of atrazine-OH and flurochloridone did not differ between landscape positions. Its moderate adsorption to the soil, low solubility and lack of relationship with soil properties caused a relatively homogeneous distribution in the landscape. It is necessary to implement crop rotations that improve soil surface properties to increase its retention and degradation and, therefore, decrease the runoff, the herbicides load in runoff and the associated environmental risks.</p>

Determination of the Environmental Pollution Potential of Some Herbicides by the Assessment of Cytotoxic and Genotoxic Effects on Allium cepa

The present study aims to evaluate the potential for the pollution of the environment by two herbicides (quizalofop-p-ethyl and cycloxydim), using the Allium test. The species in question is Allium cepa (onion, 2n = 16), one of the most common plant indicators of environmental pollution. The working method consisted of obtaining the meristematic roots of Allium cepa and their treatment with herbicides at three different concentrations (0.5%, 1%, and 1.5%) for each herbicide for 24 h, for comparison with an untreated control. The results obtained from the cytological study indicated a strong cytotoxic and genotoxic effect for both herbicides, but especially for quizalofop-p-ethyl, where the mitotic index decreased from 30.2% (control) to 9.6% for the variant treated with 1.5% herbicide. In this case, a strong mitodepressive effect was shown by a highly significant percentage (35.4%) of chromosomal aberrations and nuclear alterations: stickiness, fragments, C-mitosis, lobulated nucleus, micronuclei, and nuclear erosion. The mitodepressive effect as well as the percentage of chromosomal aberrations increased with a higher herbicide concentration. The obtained results suggest the strong potential for pollution of the two herbicides, particularly at concentrations higher than 0.5%; therefore, we recommend caution in their use to avoid undesirable effects on the environment.

Detecting herbicide-resistant Apera spica-venti with a chlorophyll fluorescence agar test

Reliable tests on herbicide resistance are important for resistance management. Despite well-established greenhouse bioassays, faster and in-season screening methods would aid in more efficient resistance detection. The feasibility of a chlorophyll fluorescence agar-based test on herbicide resistance in Apera spica-venti L. was investigated. Herbicide resistant and sensitive A. spica-venti seedlings were transplanted into agar containing pinoxaden and pyroxsulam herbicides. Chlorophyll fluorescence was measured and the maximum quantum efficiency of photosystem II (F_v/F_m) was determined 48 h and 72 h after the transplantation to agar, respectively. The F_v/F_m values decreased with increasing herbicide concentration. Dose-response curves and respective ED₅₀ values (herbicide concentration leading to 50% decrease of the F_v/F_m value) were calculated. However, each experiment repetition exhibited different sensitivities of the populations for both herbicides. In certain cases, resistant populations demonstrated similar F_v/F_m values as sensitive populations. Contrary to the findings in Alopecurus myosuroides Huds., discrimination of sensitive and resistant A. spica-venti populations was not feasible. An increased importance of the assessment time due to the herbicide concentrations calibrated for fast responses was assumed in this study.

Paraquat in Surface Water of Some Streams in Mai Chau Province, the Northern Vietnam: Concentrations, Profiles, and Human Risk Assessments

The concentrations and profiles of paraquat, a kind of herbicide, were studied in water samples taken from a stream flowing through five villages of Mai Chau province, the Northern Vietnam, during dry and rainy seasons. In this study, paraquat was found at almost the sampling sites and showed an average concentration for paraquat to be 30.69 μg/L and with a maximum of 134.08 μg/L. The herbicide concentration tended to be the highest on the dry season because of the least rainfall and also the highest evaporation rate of water in the stream. For risk assessment of human health, a hazard index (HI) value was calculated for estimating the risk towards the residents. HQ in the dry and rainy season is from 0.0001 to 0.2448 and from 0.0001 to 0.0279, respectively. The results showed a minimum risk; however, there are concerns toward the danger of long-term exposure to the residents from the stream that could affect their life quality.

Herbicidal control of bridal creeper (Asparagus asparagoides) in an ecologically sensitive environment

Asparagus asparagoides (bridal creeper) is a highly invasive noxious environmental weed in southern Australia. It poses a severe threat to biodiversity and conservation in temperate natural ecosystems. Pterostylis arenicola, a threatened terrestrial orchid endemic to South Australia, is directly imperilled by this weed in most of its remnant populations. The coincident growth phenologies of orchid and weed make for an ecologically sensitive environment when considering methods of weed control or eradication. To minimise impact on the orchid and its ecosystem, this paper examines the efficacy of herbicide application for A. asparagoides control using the weed wiping technique, comparing it to the conventional spray application method. The most prolonged control of A. asparagoides was achieved after a single wipe-application of 1.5 g a.i. (active ingredient) L−1 metsulfuron methyl, either alone or in combination with 120 g a.i. L−1 glyphosate, both treatments giving significantly better weed control five years after treatment than comparable spray applications. An investigation of the effect of glyphosate on cultures of the mycorrhizal fungus isolated from P. arenicola indicated a significant decline in mycelial growth with increasing herbicide concentration over the range 0.5–3.0 kg a.i. ha−1. These results provide further incentive for the use of ecologically sensitive herbicide application techniques, such as weed wiping, in areas of high conservation concern.

Effects of Topramezone and Bispyribac-sodium in Irrigation Water on Warm-season Turfgrasses

Topramezone and bispyribac-sodium were registered for aquatic weed control in the last decade. A primary target for these products is fluridone-resistant hydrilla (Hydrilla verticillata), which is one of the most invasive submersed weeds in the southeastern United States. Both products have water use restrictions that prohibit irrigation of turfgrasses with treated waters until the herbicides have degraded to very low concentrations. The objective of these studies was to identify the concentrations of topramezone and bispyribac-sodium that are phytotoxic to turfgrasses that are commonly planted in Florida. Three species of turfgrass were irrigated twice weekly with 0.5 inch of treated water for 4 weeks (eight irrigations total). Cumulative EC10 values (the herbicide concentration that caused a 10% reduction in biomass compared with untreated control plants) after eight irrigations with water containing topramezone were 3.5, 4.3, and 17 ppb for ‘Palmetto’ st. augustinegrass (Stenotaphrum secundatum), ‘Pensacola’ bahiagrass (Paspalum notatum), and ‘Tifway 419’ hybrid bermudagrass (Cynodon dactylon × C. transvaalensis), respectively. Bispyribac-sodium was less toxic to all turfgrasses evaluated, with EC10 values of 56, 16, and >800 ppb for ‘Palmetto’ st. augustinegrass, ‘Pensacola’ bahiagrass, and ‘Tifway 419’ hybrid bermudagrass, respectively. These results support label instructions and highlight the need to comply with irrigation restrictions because the typical use concentrations for submersed weed control with topramezone and bispyribac-sodium are in the 20–40-ppb range.

Ametryn Leaching in Soils from the Sugarcane Region in Northeastern Brazilian

ABSTRACT Ametryn is one of the most widely used herbicides in the sugarcane culture. Little is known about the interactions between this herbicide and the attributes of soils in the sugarcane region of northeastern Brazil. This knowledge, before recommending herbicide, will minimize the negative effects on the environment, particularly on water resources, and will ensure weed control efficacy. In this work, ametryn leaching potential was estimated through bioassays and chromatography, in five soils from the sugarcane region in northeastern Brazil: Quartzarenic Neosol (Entisol); Red Argisol (Ultisol); Ferrihumiluvic Spodosol (Spodosols); Red-Yellow Acrisol (Oxisol) and Haplic Cambisol (Inceptisols). To achieve this, columns were prepared with samples of the respective soils. On top of these columns ametryn was applied and, 12 hours later, a 60 mm rainfall was simulated. After water draining (72 hours after herbicide application), the columns were longitudinally opened to withdraw samples of each soil, every 5 cm. On some of these samples, ametryn quantification was performed by high-performance liquid chromatography and, on the others, biological assays were performed to confirm the results. Ametryn mobility was influenced by the physical-chemical characteristics of soils, mainly by organic matter content, texture and cation exchange capacity (CEC). However, this cannot be considered for Ferrihumiluvic Spodosol, whose cementing characteristics restrict the infiltration of water and organic compounds. Increased leaching ametryn occurred in Quartzarenic Neosol (Entisol), with higher herbicide concentration in the 5 to 10 cm depth layer, in relation to the 0 to 5 cm surface layer, indicating possible agronomic efficiency loss and higher risk of groundwater contamination.