Early Post-emergence Herbicide Research Articles

Optimization of Spray Fluid for Herbicide Application for Drones in Irrigated Maize (Zea mays L.)

A field experiment was conducted in a randomized complete block design to screen the optimum spray fluid of herbicide application for drone based on visual toxicity and weed control efficiency in maize (Zea mays L.) during the summer season (March 2021) at eastern block farms of Tamil Nadu Agricultural University, Coimbatore, Tamil Nadu. Three herbicide treatments namely Atrazine, Tembotrione and 2, 4-D with recommended dosages, 75% and 125% as pre-emergence herbicides applied on 3 days after, early post-emergence herbicides applied on 15 days after sowing and post-emergence applied on 25 days after sowing respectively. Totally thirty treatments with different spray fluids such as 500, 400, 300, 200, 100, 80, 60, 40, 30 L ha-1 and 20 L ha-1 were replicated three times. The study revealed that T5- Recommended dosage of pre emergence Atrazine – early post emergence Tembotrione – post emergence 2, 4-D (spray fluid 100 L of water ha-1),T6- Recommended dosage of pre emergence Atrazine – early post emergence Tembotrione–post emergence 2, 4-D (spray fluid 80 L of water ha-1), T7- Recommended dosage of pre emergence Atrazine – early post emergence Tembotrione – post emergence 2, 4-D (spray fluid 60 L of water ha-1) and T8- Recommended dosage of pre emergence Atrazine – early post emergence Tembotrione – post emergence 2, 4-D (spray fluid 40 L of water ha-1) produced the best results with respect to phytotoxicity and weed control efficiency. Based on the results it was concluded that the application of spray fluid 80 L ha-1 was optimum for herbicide application through drones with recommended dosage pre emergence Atrazine 1 kg a.i ha-1 on 3 days after sowing – early post emergence Tembotrione 120 g a.i ha-1 on 15-20 days after sowing - post emergence 2, 4-D 1 kg a.i ha-1 on 30 - 35 days after sowing.

Allelopathic and Herbicidal Effects of Crude Extract from Chromolaena odorata (L.) R.M.King and H.Rob. on Echinochloa crus-galli and Amaranthus viridis.

The present study was aimed at investigating the allelopathic effects of a crude extract from Chromolaena odorata (L.) R.M.King and H.Rob. (Siam weed). The effects of 70% crude ethanol extract from the whole plant, leaf, stem, and root on the germination and growth of Echinochloa crus-galli and Amaranthus viridis seedlings were evaluated using Petri-dish tests under laboratory conditions. Crude extracts from the leaf showed the highest inhibitory activity. The leaf extract (OR) was further separated by sequential solvent extraction to provide hexane (HX), ethyl acetate (ET), and butanol (BU) fractions, which were also evaluated using Petri-dish tests. The hexane fraction was significantly the most active; therefore, it was selected for formulation in a concentrated suspension and tested for its herbicidal characteristics. The formulation showed greater early post-emergence than post- and pre-emergence activities, respectively. The physiological mechanism of the formulation was tested against E. crus-galli and showed that chlorophyll a and b and the carotenoid contents of the leaf dramatically decreased when the concentration was increased, suggesting its ability to disrupt the process of photosynthesis. As thiobarbituric acid reactive substances also occurred in the leaf of E. crus-galli, this suggests lipid peroxidation and cell disruption. These results represent the possibility that C. odorata extract contains inhibitory compounds with herbicidal activity and could be used as an early post-emergence herbicide for weed control.

Control of glyphosate‐ and mesotrione‐resistant Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn

AbstractIncreasing reports of herbicide‐resistant Palmer amaranth (Amaranthus palmeri S. Watson) pose a serious management concern for Kansas corn (Zea mays L.) producers. The objectives of this study were to evaluate various herbicide programs, including preemergence (PRE) alone, PRE followed by (fb) early postemergence (EPOST), and PRE fb late POST (LPOST) for control of glyphosate‐ and mesotrione‐resistant (GMR) Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn, and their effect on crop injury, yield, and net economic return. Field experiments were conducted in 2018 and 2019 in grower fields with natural infestations of GMR Palmer amaranth near Seward in Stafford County, KS. Preemergence programs, including dicamba + thiencarbazone‐methyl + atrazine and dicamba + [atrazine, bicyclopyrone, mesotrione, S‐metolachlor (ABMS)] or dicamba + ABMS in mixtures with atrazine, mesotrione, S‐metolachlor, and metribuzin provided 89–93% control of GMR Palmer amaranth 3 wk after PRE. Preemergence fb EPOST programs provided 87–96% control of GMR Palmer amaranth at 2 wk after EPOST through 7 wk after LPOST. In comparison, PRE‐only programs provided 62–82% and PRE fb LPOST programs provided 75–86% control. The various herbicide programs resulted in greater corn grain yield ranging from 9,207 to 10,508 kg ha–1 compared with 6,056 kg ha–1 in the nontreated control. The highest net return ($1,300 ha–1) was achieved from dicamba + ABMS + atrazine applied PRE fb EPOST application of ABMS + atrazine. These results suggest that effective PRE fb EPOST herbicide programs consisting of multiple sites of actions are available and provide effective control of GMR Palmer amaranth in glyphosate‐ and glufosinate‐resistant corn.

The Herbicide Atrazine Potentiates Angiotensin II-Induced Aldosterone Synthesis and Release From Adrenal Cells.

Atrazine is one of the most commonly used pre-emergence and early post-emergence herbicides in the world. We have shown previously that atrazine does not directly stimulate the pituitary or adrenal to trigger hormone release but acts centrally to activate a stress-like activation of the hypothalamic-pituitary-adrenal axis. In doing so, atrazine treatment has been shown to cause adrenal morphology changes characteristic of repeated stress. In this study, adrenals from atrazine treated and stressed animals were directly compared after 4 days of atrazine treatment or restraint stress. Both atrazine and stressed animals displayed reduced adrenocortical zona glomerulosa thickness and aldosterone synthase (CYP11B2) expression, indicative of repeated adrenal stimulation by adrenocorticotropic hormone. To determine if reduced CYP11B2 expression resulted in attenuated aldosterone synthesis, stressed and atrazine treated animals were challenged with angiotensin II (Ang II). As predicted, stressed animals produced less aldosterone compared to control animals when stimulated. However, atrazine treated animals had higher circulating aldosterone concentrations compared to both stressed and control groups. Ang II-induced aldosterone release was also potentiated in atrazine pretreated human adrenocortical carcinoma cells (H295R). Atrazine pretreated did not alter the expression of the rate limiting steroidogenic StAR protein or angiotensin II receptor 1. Atrazine treated animals also presented with higher basal blood pressure than vehicle treated control animals suggesting sustained elevations in circulating aldosterone levels. Our results demonstrate that treatment with the widely used herbicide, atrazine, directly increases stimulated production of aldosterone in adrenocortical cells independent of expression changes to rate limiting steroidogenic enzymes.

Effects of pendimethalin on pod attributes of five elite accessions of cowpea

A field study on the effects of pre- and post-emergence application of herbicide (pendimethalin) on the reproductive yield of five accessions of cowpea (TVu-9092, TVu-16265, TVu-16320, TVu-16323 and TVu-16421) was conducted between June and August, 2018. Pendimethalin was applied both as pre- and early post-emergence herbicide (PE and EPOE) and followed by hand weeding at 4 and 8 weeks after sowing (WAS). Number of pods per plant was highest in TVu-9092 treated with 0.125 kg/ha PE pendimethalin (19.33) and 0.250 kg/ha pendimethalin EPOE application (19.00). Highest pod diameter in PE treatment was produced in TVu-16320 with 0.25 kg/ha pendimethalin (7.55 mm) and TVu-16323 with 0.125 kg/ha pendimethalin produced the highest pod diameter (7.74 mm) in the EPOE treatment. Highest pod length in the PE treatment was produced in TVu-9092 with 0.125 kg/ha, while TVu-9092 without pendimethalin produced the highest pod length (30.00 cm) in the EPOE treatment. In the PE treatment, TVu-16265 and TVu-9092 treated with 0.125 kg/ha had the highest (2.99 g) and lowest empty pod weights (1.70 g) respectively. In the EPOE treatment, the highest empty pod weight (3.01 g) was produced in TVu-16265 with 0.125 kg/ha pendimethalin while the control of TVu-16320 recorded the lowest empty pod weight (2.03 g). The highest of 100 seeds weight (14.91 g) was produced in TVu-16421 with 0.125 kg/ha pendimethalin PE treatment and lowest (9.26 g) was obtained in the untreated control of TVu-16323. In the post-emergence treatment, the lowest 100 seeds weight (8.88 g) was obtained in TVu-16320 with 0.125 kg/ha. Highest weight per pod in the PE and EPOE application was obtained in untreated control with TVu-9092 (10.47 g), while the lowest weight per pod (3.22 g) was in TVu-16265 with 0.125 kg/ha EPOE application. The study concluded that pendimethalin application as pre- and early post-emergence herbicide at low and high concentrations produced varying effects on pod attributes among the accessions of cowpea.

Low Effectiveness of Prosulfocarb and Mesosulfuron-Methyl + Iodosulfuron-Methyl against Vulpia myuros.

Due to natural tolerance to most widely used herbicides for grass weed control, prosulfocarb as pre-emergence or early post-emergence herbicide and mesosulfuron + iodosulfuron as post-emergence herbicide are the mainstays of any chemical control program for Vulpia myuros in Denmark. However, farmers often report variable efficacy of these herbicides on V. myuros compared to other grass weeds. Dose–response experiments were conducted to evaluate the performance of prosulfocarb and mesosulfuron + iodosulfuron on V. myuros. Prosulfocarb was sprayed at different plant growth stages to study the influence of plant growth stage on the performance of prosulfocarb on V. myuros in comparison with the more susceptible grass weed species Apera spica-venti. Doses causing 50% reduction in response variable (ED50) were estimated from the dose–response analysis. The ED50 values revealed a higher tolerance of V. myuros to prosulfocarb and mesosulfuron + iodosulfuron than A. spica-venti. The relative difference in the effectiveness of prosulfocarb between V. myuros and A. spica-venti was constant among plant growth stages studied. The highest levels of V. myuros control were achieved when prosulfocarb was sprayed pre-emergence (BBCH 00), while the control substantially declined at later growth stages. The results from the current study document the tolerance of V. myuros to prosulfocarb and mesosulfuron + iodosulfuron and highlight the importance of optimization of prosulfocarb spray timing for achieving maximum control of V. myuros.

Enhancing Rice Yield and Weed Management in Direct Seeded Rice Using Ammonium Sulfate as Adjuvant with Lower Dose of Early Postemergence Herbicides

A field experiment was conducted in 2016 to find out the sequential use of different herbicides with adjuvants (a substance which enhances pesticides efficiency) towards improved rice production and weed management in direct-seeded rice crop. The early postemergence herbicides (Kelion 50 WG, Ryzelan 240 SC, and Nominee 100 SC were applied at full or 75% of the full dose with and without adjuvants i.e. 2% solution of ammonium sulfate (AS) and alkyl ether sulfate (AES) at 14 days after sowing (DAS), followed by late postemergence herbicides i.e. Puma super (7.5 EW) and Sunstar 60 WG at 28 DAS. Application of herbicides with and without adjuvant substantially suppressed weed with weed dry weight at 40 and 60 DAS and improved rice yield attributes over a weedy check. It was found that a combination of 75% of Nominee 100 SC along with adjuvant i.e. AS (2% v/v) resulted in higher biological yield (9.16 t/ha), harvest index (30.65%), more grains per panicle (98.13), 1000 grain weight (21.32 g) with improved seed yield (3.86 t/ha). Also, abortive kernel (5.33), chalky kernels (5.66), opaque kernels (5.00), normal kernel (70.66), water absorptive ratio (4.28), and kernel length (10.13).

Early Postemergence Herbicide Tank-Mixtures for Control of Waterhemp Resistant to Four Herbicide Modes of Action in Corn

Multiple-herbicide-resistant (MHR) waterhemp has been confirmed and is difficult to control for growers in Ontario, Canada and in the Midwestern United States. The objective of this study was to evaluate early post-emergence (EPOST) herbicides for control of MHR waterhemp in field corn. Five field trials were conducted over a two-year period (2019, 2020) at sites on Walpole Island, ON and near Cottam, ON, Canada. Thirteen herbicide tank-mixtures containing multiple modes-of-action (MOA) were applied EPOST to 5 cm MHR waterhemp in field corn. Control of MHR waterhemp varied by site due to variable plant density, plant biomass, and number of herbicide-resistant individuals across research sites and years. Control of MHR waterhemp ranged from 90% to 100% with glyphosate + S-metolachlor/mesotrione/ bicyclopyrone/atrazine, glyphosate/2,4-D choline + rimsulfuron + mesotrione + atrazine, glyphosate + S-metolachlor/atrazine/mesotrione, glyphosate + mesotrione + atrazine, glyphosate/S-metolachlor/mesotrione + atrazine, glyphosate + S-metolachlor/mesotrione/bicyclopyrone, glyphosate/2,4-D choline + rimsulfuron + mesotrione, and glyphosate + pyroxasulfone + dicamba/atrazine at 4, 8, and 12 WAA. Control of MHR waterhemp ranged from 70% to 100% with glyphosate + topramezone/dimethenamid-P + dicamba/atrazine, glyphosate + isoxaflutole + atrazine, and glyphosate + tolpyralate + atrazine at 4, 8, and 12 WAA. Control of MHR waterhemp was similar for all herbicide programs, except glyphosate + dicamba/atrazine and glyphosate + S-metolachlor/atrazine which resulted in the lowest control at three of five sites that ranged from 63% to 89% and 61% to 76%, respectively. Crop injury was ≤10% for herbicide programs tested, except 28% to 31% corn injury with glyphosate/2,4-D choline + rimsulfuron + mesotrione + atrazine; however, without effect on corn grain yield. Corn yield was comparable with all herbicide programs evaluated in this study. It is concluded that there are herbicide programs that provide control of emerged and full-season residual control of MHR waterhemp in field corn.

Efficacy of sequential application of pre- and early post-emergence herbicides for management of weeds in blackgram

Efficacy of sequential application of pre- and early post-emergence herbicides for management of weeds in blackgram

Weed Dynamics and Productivity of Direct Wet Seeded Rice under Different Weed Management Practices

Background: Weeds are the major biotic constraint to reduce the rice productivity in direct wet seeded rice. Weed infestation and competition are severe in direct wet seeded rice as compared to transplanted rice, because of the simultaneous growth of both crops and weeds. The yield loss due to weeds varies from 40 to 100 per cent in direct seeded rice. Use of herbicides either singly or in combination with manual or mechanical weeding in puddled direct seeded rice has been highlighted by several workers. Use of alternative herbicides with wide spectrum control of the weeds in direct seeded puddled rice is the need of the present time. The present study aimed to evaluate different weed management practices in direct wet seeded rice under sodic soil.Methods: A field experiment was conducted during Samba season (Rabi) 2016-17. to evaluate the weed management practices in direct wet seeded rice under sodic soil. The treatments comprised of different combination of weed management practices viz., pre emergence, early post emergence herbicides, mechanical weeding and hand weeding twice were tested. Total weed density and weed dry weight, weed control efficiency, yield parameters and yield of rice were recorded. Result: Among the different weed management practices, the lowest total weed density, total weed dry weight and higher WCE, yield attributes, grain and straw yields were registered under application of PE pyrazosulfuron ethyl 25 g/ha fb EPOE bispyribac sodium 25 g/ha. This was followed by application of PE pretilachlor 0.75 kg/ha fb EPOE bispyribac sodium 25 g/ha.

Studies on pre and post emergence herbicidal weed management in hybrid maize COH (M)6 (Zea mays)

In general, Maize is one of the most important cereal crops in the world’s agricultural economy both as food for human being and feed for animals. Among the cereals, maize is the important cereal crop next to rice and wheat. Weeds are generally vigorous growers and their nutrient requirements are often greater than that of crop plants. Major area of maize in India is during Kharif season in which weed is one of the important yield limiting factor and significantly reduces the yield. Hence this condition the research sub project is proposed to evaluate suitable recommendations and combination of pre and early post emergence application herbicide management for hybrid maize CO (MH) 6. A field experiment was conducted during 2016 (Aug –Sep), 2017 (Aug –Sep),& 2018 (Jan- Feb) at Agricultural Research Station, Vaigai Dam The treatment consisted that alachlor 1.25kg ha-1 with addition of one hand weeding on 30 DAS, alachlor 1.0 kg ha-1coupled with tembotrione 120g ha-1 on 30 DAS, atrazine 0.5 kg ha-1with addition of one hand weeding on 30 DAS, atrazine 0.5 kg ha-1coupled with early post emergence herbicide of Tembotrione 120 g ha-1, Tembotrione 120g ha-1alone, hand weeding twice on 20 and 40 DAS and control (Unweeded control). From the experiments it can be concluded that the pre-emergence application of Atrazine 0.5 kg ha-1 with addition with addition of early post emergence herbicide of Tembotrione 120g ha-1has recorded higher grain and stover yield.

Effect of Pre and Early Post Emergence Herbicides on Weed Control in Irrigated Blackgram (Vigna mungo L.)

Field experiment was conducted to find out the effect of pre-emergence(PE) and early post-emergence (EPoE) herbicides on weed control inirrigated blackgram at College of Agricultural Technology, Kullapuram- Theniduring 2015-2016. In this experiment, weed management practice of preemergenceapplication of Pendimethalin 30 EC 1.0 kg a.i. ha-1 at 3 daysafter sowing (DAS), early post-emergence application of Quizalofop ethyl@50 g a.i. ha-1 at 15 DAS, early post-emergence and Imazethapyr each @50 g a.i. ha-1 at 15 DAS and their combinations of Pendimethalin @ 1.0 kgha-1 at 3 DAS followed by either Quizalofop ethyl or Imazethapyr each @50 g a.i. ha-1 were tested against hand weeding twice at 20 and 40 DAS,weedy check and weed-free check as controls in randomized block designreplicated thrice. Among the different weed management practices, preemergenceapplication of Pendimethalin 1.0 kg a.i. ha-1 (3 DAS) followedby Imazethapyr @ 50g a.i. ha-1 as EPoE (15 DAS) recorded relatively lesserproportion of broad-leaved weeds (30.90 and 49.16%) and higher WeedControl Efficiency (WCE) of 91.27 at 60 DAS. Application of pendimethalin1.0 kg a.i. ha-1 PE (3 DAS) followed by Imazethapyr @ 50g a.i. ha-1 as EPoE(15 DAS) registered significantly taller plants (42.22 cm), higher dry matterproduction(2649 kg ha-1), more number of pods per plant (44.19), seedsper pod(5.57) and higher grain yield (1052 kg ha-1). Thus, pre-emergenceapplication of pendimethalin 1.0 kg a.i. ha-1 (3DAS) followed by Imazethapyr@ 50g a.i. ha-1 as EPoE (15DAS) recommended as effective and economicweed management practices on the basis of better weed control, crop growth,and yield of irrigated blackgram.

Assessment of anilofos-induced mutagenicity in bone marrow and germ cells of Swiss albino mice.

Anilofos is an organophosphate compound and is used extensively as a preemergence and early postemergence herbicide for the management of sedges, annual grasses, and some broad-leaved weeds in rice fields. The present study was aimed to assess the mutagenic potential of anilofos after sub-chronic exposure in Swiss albino mice. For this, a combined approach employing micronucleus (MN), chromosomal aberration (CA) studies and sperm-head abnormalities (SHAs) was used. Three dose levels of 1%, 2%, and 4% of maximum tolerated dose (MTD) (235 mg/kg b.wt.), that is, 2.35, 4.7 and 9.4 mg/kg b.wt., respectively, were administered orally daily for 90 days. A higher incidence of micronucleated erythrocytes (polychromatic erythrocytes + normochromatic erythrocytes), significant increase in CA frequency, and significant decrease in the ratio of polychromatic/normochromatic erythrocytes (P/N) ratio were observed at the 4.7 and 9.4 mg/kg b.wt. dose levels. A significant increase in SHA was observed in all treatment groups (2.35, 4.7, and 9.4 mg/kg b.wt.) from the control group. In conclusion, anilofos exposure of 2% and 4% of MTD caused a higher rate of micronucleated erythrocytes, increased frequency of CA, increase in SHA, and lower P/N ratio, and pesticide exposure of 1% of MTD only resulted in higher SHAs. Thus, anilofos was found to have mutagenic potential in mice when administered daily orally at dose rate of 4.7 and 9.4 mg/kg b.wt. for 90 days.

Early Postemergence and Sequential Herbicides for Weed Control in Corn

Early Postemergence and Sequential Herbicides for Weed Control in Corn

Effect of weeding regime on the performance of boro rice cultivars

An experiment was conducted at the Agronomy Field Laboratory, Bangladesh Agricultural University, Mymensingh from December 2016 to May 2017 to investigate the effect of weeding regime on the performance of boro rice cultivars. The experiment comprised of two factors, Factor A- Rice cultivars: BRRI dhan28, BRRI dhan29, and BRRI dhan74, Factor B: Methods of weeding- no weeding, two hand weedings at 15 and 35 DATs, application of pre-emergence herbicide Commit, application of early post-emergence herbicide Pediplus, application of pre-emergence herbicide Commit followed by application of early post-emergence herbicide Pediplus, application of pre-emergence herbicide Commit followed by one hand weeding at 35 DAT, and application of early post-emergence herbicide Pediplus followed by one hand weeding at 35 DAT. The experiment was laid out in a split plot design assigning rice cultivars in the main plots and weed management practices in the sub-plots with three replications. Fourteen weed species infested the experimental field belonging to six families. Among the weed species, four were grasses, four were broad leaves and six were sedges. Cultivar exerted significant effect on weed density and dry weight. Both the highest weed density and dry weight were found in BRRI dhan28 and the lowest ones were observed in BRRI dhan29 rice cultivar. Weed density and weed dry weight were significantly influenced by weeding regime. The highest weed density and dry weight were observed in no weeding condition and application of pre-emergence herbicide Commit followed by one hand weeding at 35 DAT showed the best performance. BRRI dhan29 produced the highest grain and straw yields among the cultivars. Weed control had pronounced influence on yield of rice. The highest grain yield was obtained in application of pre-emergence herbicide Pretilachlor (Commit)followed by one hand weeding at 35 DAT and the lowest one was obtained in control (no weeding) treatment. From the results of the study it may be concluded that rice cultivar BRRI dhan29 with application of pre-emergence herbicide Commit followed by one hand weeding at 35 DAT might be the best treatment for controlling weed effectively as well as obtaining highest yield and highest economic return.
 J Bangladesh Agril Univ 17(3): 265–273, 2019

Anthem Maxx Tank Mixture Comparisons in Irrigated Corn

The use of multiple herbicide modes of action in single versus sequential applications was examined for efficacy in corn. Common sunflower control was complete with all early postemergence and postemergence herbicides late in the season. Control of Russian thistle, Palmer amaranth, and green foxtail were 95% or more with all early postemergence and postemergence herbicides except Halex GT. All herbicide treatments increased grain yield 15–33% compared to the nontreated controls except Halex GT applied early postemergence.

Residual effect of pre-sowing weed management on the purple nutsedge (Cyperus rotundus) and succeeding maize germination and yield

A study was carried out to evaluate different pre-sowing weed management methods on Cyperus rotundus and on succeeding maize germination and yield at Chinnankuppam village in Dharmapuri district, Tamil Nadu. Pre-emergence, early post-emergence and post-emergence herbicides viz metribuzin, halosulfuron methyl, glyphosate and 2, 4-D were applied at different doses to select an optimum dose suitable for the management of purple nutsedge (C rotundus) as a pre-sowing weed management method. Pre-sowing weed management treatments did not influence the per cent germination of succeeding maize. Among the pre-sowing weed management treatments early postemergence application of halosulfuron methyl at 50 g/ha followed by post-emergence application of glyphosate at 1.00 g/ha resulted in reduced density and dry weight (2.2 and 4.1/m2, 0.37 and 0.70 g/m2) followed by early postemergence application of halosulfuron methyl at 75 g/ha (3.5 and 5.7/m2, 0.60 and 0.97 g/m2) at 15 and 30 DAS respectively. Simultaneously both the treatments increased the weed control efficiency of C rotundus (69.16 and 58.33%) and (50.00 and 42.26%) at 15 and 30 DAS respectively. Among the treatments pre-sowing application of early post-emergence halosulfuron methyl at 50 g/ha followed by post-emergence application of glyphosate at 1.00 kg/ha recorded the higher grain (9, 387 kg/ha)and stover (9, 500 kg/ha) yield of succeeding maize.

Oxadiazon affects the expression and activity of aldehyde dehydrogenase and acylphosphatase in human striatal precursor cells: A possible role in neurotoxicity

Exposure to herbicides can induce long-term chronic adverse effects such as respiratory diseases, malignancies and neurodegenerative diseases. Oxadiazon, a pre-emergence or early post-emergence herbicide, despite its low acute toxicity, may induce liver cancer and may exert adverse effects on reproductive and on endocrine functions. Unlike other herbicides, there are no indications on neurotoxicity associated with long-term exposure to oxadiazon. Therefore, we have analyzed in primary neuronal precursor cells isolated from human striatal primordium the effects of non-cytotoxic doses of oxadiazon on neuronal cell differentiation and migration, and on the expression and activity of the mitochondrial aldehyde dehydrogenase 2 (ALDH2) and of the acylphosphatase (ACYP). ALDH2 activity protects neurons against neurotoxicity induced by toxic aldehydes during oxidative stress and plays a role in neurodegenerative conditions such as Alzheimer's disease and Parkinson's disease. ACYP is involved in ion transport, cell differentiation, programmed cell death and cancer, and increased levels of ACYP have been revealed in fibroblasts from patients affected by Alzheimer's disease. In this study we demonstrated that non-cytotoxic doses of oxadiazon were able to inhibit neuronal striatal cell migration and FGF2- and BDNF-dependent differentiation towards neuronal phenotype, and to inhibit the expression and activity of ALDH2 and to increase the expression and activity of ACYP2. In addition, we have provided evidence that in human primary neuronal precursor striatal cells the inhibitory effects of oxadiazon on cell migration and differentiation towards neuronal phenotype were achieved through modulation of ACYP2. Taken together, our findings reveal for the first time that oxadiazon could exert neurotoxic effects by impairing differentiative capabilities of primary neuronal cells and indicate that ALDH2 and ACYP2 are relevant molecular targets for the neurotoxic effects of oxadiazon, suggesting a potential role of this herbicide in the onset of neurodegenerative diseases.

English

Manual weeding, maize-cowpea intercropping, pre-emergence (PRE) and early post-emergence (EPOST) herbicide applications comprised ten weed control practices evaluated in the 2015-16 cropping season on weed species structure and maize (Zea mays L.) yield in the Middleveld and Highveld of Swaziland. The herbicides used were Harness (acetochlor) and Dual Gold (S-metolachlor) as pre-emergence applications and Micro-Tech (alachlor) and Callisto (mesotrione) as early post-emergence applications. PRE and EPOST herbicides were used as once-off or combined applications besides manual weeding or intercropping practices. Results indicated that the combination of PRE and EPOST herbicides reduced both species richness (number) and evenness (dominance) but weed species composition (types) were not distinguished amongst treatments. Manual weeding in combination with PRE herbicides or maize-cowpea intercropping resulted in significantly lower weed density and biomass as compared to singular or combinations of PRE or EPOST herbicides in both locations. The effects of weed control practices on grain yield of maize were not significantly distinguished among weed control practices between the two sites. The study reaffirmed that herbicides may need to be supplemented with other weed control strategies to obtain acceptable weed control. Key words: Herbicides, maize, Shannon-Wiener diversity index, Simpson’s dominance index, Steinhaus coefficient index, weeds.

Characterization of Activation of the Hypothalamic-Pituitary-Adrenal Axis by the Herbicide Atrazine in the Female Rat.

Atrazine (ATR) is a commonly used pre-emergence and early postemergence herbicide. Rats gavaged with ATR and its chlorometabolites desethylatrazine (DEA) and deisopropylatrazine (DIA) respond with a rapid and dose-dependent rise in plasma corticosterone, whereas the major chlorometabolite, diaminochlorotriazine (DACT), has little or no effect on corticosterone levels. In this study, we investigated the possible sites of ATR activation of the hypothalamic-pituitary-adrenal (HPA) axis. ATR treatment had no effect on adrenal weights but altered adrenal morphology. Hypophysectomized rats or rats under dexamethasone suppression did not respond to ATR treatment, suggesting that ATR does not directly stimulate the adrenal gland to induce corticosterone synthesis. Immortalized mouse corticotrophs (AtT-20) and primary rat pituitary cultures were treated with ATR, DEA, DIA, or DACT. None of the compounds induced an increase in ACTH secretion or potentiated ACTH release in conjunction with CRH on ACTH release. In female rats gavaged with ATR, pretreatment with the CRH receptor antagonist astressin completely blocked the ATR-induced rise in corticosterone concentrations, implicating CRH release in ATR-induced HPA activation. Intracerebroventricular infusion of ATR, DEA, and DIA but not DACT at concentrations equivalent to peak plasma concentrations after gavage dosing resulted in an elevation of plasma corticosterone concentrations. However, ATR did not induce c-Fos immunoreactivity in the paraventricular nucleus of the hypothalamus. These results indicate that ATR activates the HPA axis centrally and requires CRH receptor activation, but it does not stimulate cellular pathways associated with CRH neuronal excitation.