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Persistence and leaching of imazethapyr and flumetsulam herbicides over a 4-year period in the highly alkaline soils of south-eastern Australia
Abstract
Imazethapyr and flumetsulam are acetolactate synthase herbicides commonly used in the cereal belt of south-eastern Australia. As their labels recommend recropping periods of up to 34 months for imazethapyr and 24 months for flumetsulam, there are concerns that in some cases their persistence may damage subsequent rotation crops. This is the first major study in south-eastern Australia to investigate their leaching and persistence for up to 4 years after treatment. Imazethapyr persisted for more than 3 years at 2 sites and flumetsulam for more than 2 years at 3 sites. For imazethapyr, soil type (clay content) rather than soil pH seemed to be most important in determining persistence, with residues of 10% of applied imazethapyr predicted to persist for 24 months after treatment in clay soil and 5 months after treatment in sandy soil. The potential for leaching below our studied soil depth of 40 cm is of concern for imazethapyr but not for flumetsulam. The current labels appear to provide adequate information for safe recropping periods, but may be conservative for imazethapyr in sandy soils.
... Based on the findings of experiment, the response of plant roots and shoot biomass to the simulated imazethapyr residues follows the logistic model which is accordance with results from other studies (Halloway et al., 2006;Santin-Montanya et al., 2006). The results showed that the imazethapyr residues in concentrations of 0.002-0.04 ...
... In bioassay studies of herbicides residues in soil, root growth of plants is one of the most important indicators in assessing the sensitivity of plant species to herbicide residues and determining the probable amounts of their residues. In this regard, Halloway et al. (2006) reported that the sensitivity of lentil root growth to metsulfuron methyl residues was an appropriate index for determining the possible residues of this herbicide in agricultural soils. They reported that, despite the inability of analytical methods to detect device the herbicide residues, lentil root bioassay test was a suitable measure for the detection of metsulfuron methyl residues. ...
Imazethapyr is one of imidazolinone herbicides that may leave residual activity in the soil for extended periods causing injury and yield reduction of susceptible crops in rotation. An experiment was conducted in order to study the sensitivity of oilseed rape (Brassica napus L.) to imazethapyr soil residues. Experimental type was completely randomized design with three replications. Treatments included Imazethapyr simulated concentrations residuals in soil (0.002, 0.004, 0.008, 0.012, 0.02 and 0.04 mg. kg soil). Shoot and root biomass production was measured 30 days after emergence. Oilseed
rape responses to imazethapyr residues was fitted with sigmoidal 3 and 4 parametric equations to the root and shoot biomass data as a function of the herbicide residue concentrations and was used to calculate the doses for 50% inhibition of root and shoot growth (ED ). Results showed that the oilseed rape shoot and root dry matter were significantly affected -1 50 by increasing imazethapyr soil residue (p<0.01). This reduction in root dry matter was severe than shoot dry matter, where root ED (0.0019 mg.kg soil) was less than shoot dry matter (0.0025 mg.kg soil). Considering the high sensitivity
50 -1 -1 of oilseed rape to imazatepara residues, attention is needed to provide oilseed rape cultivation in fields with a history of imazateaper application.
... A low concentration of imazethapyr in soil is also compensated for high microbial activity, which increases the rate of degradation. 6,8,30,[32][33][34][35][36] O'Sullivan et al. 21) reported imazethapyr residues mainly in the top 0-10 cm soil fraction; however, some quantity of imazethapyr residue was found at 10-20 and 20-40 cm depths, also. Besides the organic matter, clay can also play an important role in the degradation of pesticides. ...
... Besides the organic matter, clay can also play an important role in the degradation of pesticides. However Hollaway et al. 34) reported the persistence of imazethapyr residues for 24 and 5 months in clay and sandy soils, respectively. Though the soils in all five locations were low in organic carbon contents, residues were detected below the maximum residue limits in plant samples. ...
Imazethapyr is widely used in soybean, and leguminous crops for control of wide variety of broad leaf weed species. A study was conducted to evaluate residues of imazethapyr in the soil and soybean grain at five different locations in India. Imazethapyr was applied at 100 g/ha, as a post emergence herbicide to control weeds in soybean fields. Residues of imazethapyr were found in the range from 0.006 to 0.018 μg/g in the soybean grains samples in all five locations. However in the soil, residues were found to be below 0.0010 μg/g in four locations, and 0.0015 μg/g in one location. Less residues were found in soils as compared to plant samples. Based on this study a pre-harvest interval of 90-102 days is suggested for soybean crops after imazethapyr application. This indicates the judicious use of imazethapyr by farmers in soybean fields.
... É absorvido pelas raízes e folhas (TAN et al., 2005) e transportado pelo floema e xilema, acumulando-se nos pontos de crescimento. O controle é proporcionado pela inibição da enzima acetolactato sintetase (ALS), que é essencial no processo de síntese de aminoácidos de cadeias ramificadas em plantas, como a valina, leucina e isoleucina (TAN et al., 2006). ...
... maiores concentrações se encontrassem nos primeiros 10cm. A maior concentração do produto, aos 30DAA, foi detectada nos primeiros 15cm, embora tenha ocorrido até 30cm de profundidade. A partir dos 90DAA, a concentração, nos primeiros cinco centímetros, diminuiu, concentrando-se o herbicida entre 5 e 30cm de profundidade. De acordo com HOLLAWAY et al. (2006), o imazethapyr pode permanecer no solo por mais de três anos e alcançar até 40cm de profundidade. O imazethapyr e imazapyr lixiviam rapidamente após uma chuva; porém, durante o processo natural de perda de umidade do solo, o herbicida movimenta-se para cima, conduzido pelas correntes de evapotranspiração (VAN WYK & REINHARDT, 2001; FIRM ...
O imazethapyr está sendo amplamente utilizado no Rio Grande do Sul desde o desenvolvimento da Tecnologia Clearfield® (CL) em arroz, em uma mistura formulada de imazethapyr + imazapic (75 + 25g L-1). No entanto, com o uso dessa tecnologia, surgiu o problema da persistência do herbicida no solo, afetando cultivos não tolerantes em sucessão com diferentes intensidades. A fitointoxicação está relacionada, dentre vários fatores, à localização do herbicida no perfil do solo. O presente trabalho teve por objetivo determinar o posicionamento do imazethapyr em profundidade, no perfil de um solo de várzea cultivado com arroz, frente a dois tipos de manejo. Foram coletadas amostras de solos, em diferentes profundidades (0-5, 5-10, 10-15 e 15-20cm), do solo de várzea sob dois sistemas de manejo: plantio convencional (PC) e plantio direto (PD), em uma área onde havia sido utilizado arroz CL por dois anos e no terceiro ano, arroz não tolerante. A concentração do herbicida no solo foi analisada por HPLC-DAD. Há maior concentração de imazethapyr na superfície do solo (0-5cm), no sistema convencional, quando comparado com o sistema de plantio direto, e o herbicida lixiviou até 20cm nos dois sistemas. No PC, ocorreu uma distribuição uniforme do imazethapyr nos primeiros 15cm de solo, enquanto que, no PD, constatou-se acúmulo de imazethapyr nas camadas de 5-10 e 10-15cm.
... Loux and Reese (1993) reported half-lives of imazethapyr in plots of silt loam soil that ranged from 70 to 119 d with less than normal rainfall but were considerably shorter (14-21 d) when rainfall was normal. Hollaway et al. (2006) reported half-lives of imazethapyr in three soils that varied from <56 to <126 d. Th us, the persistence of imazamethabenz-methyl and imazethapyr in soil indicates availability for leaching. ...
... Aft er fall applications of imazamethabenz-methyl to fi eld plots, Jensen et al. (1997) reported concentrations of the herbicide in the 20-to 30-cm soil layer were greater for loamy sand soil than for a clay loam soil. Hollaway et al. (2006) reported leaching of imazetha-pyr into the 20-to 40-cm soil layer in highly alkaline soils, and Goetz et al. (1990) detected imazethapyr in the 7.5-to 15-cm layer of silt loam and silty clay soils. Using undisturbed soil columns (30-cm diameter by 68-cm length), O'Dell et al. (1992) established breakthrough curves for imazethapyr and reported that, aft er the addition of two pore volumes of water to the column, approximately 60% of the applied amount was recovered in the leachate. ...
Some imidazolinone herbicides have been shown to be mobile in soil, raising concern about their possible movement to ground water. Three imidazolinone herbicides (imazamethabenz-methyl, 497 g ha(-1); imazethapyr, 14.7 g ha(-1); and imazamox, 14.7 g ha(-1)) commonly used in crop production on the Canadian prairies were applied to a tile-drained field to assess their susceptibility to leach when subjected to sprinkler irrigation using a center pivot. Tile-drain flow began when the water table rose above tile-drain depth, and peak flow rates corresponded to the greatest depths of ground water above the tile drains. Interception of irrigation water by the tile drains in each quadrant of the field varied from ∼11 to 20% of the water applied. Under a worst-case scenario in which irrigation began the day after herbicide application and irrigation water was applied at 25 mm d(-1) for 12 d, there was evidence of preferential flow of all three herbicides and hydrolysis of imazamethabenz-methyl to imazamethabenz in the initial samples of tile-drain effluent. In subsequent samples, concentrations (analysis by LC-MS-MS) of the summation of imazamethabenz-methyl (25-24,000 ng L(-1)) plus its hydrolysis product imazamethabenz (63-26,500 ng L(-1)) greatly exceeded those of imazethapyr (<13-1260 ng L) and imazamox (19-599 ng L(-1)), thus reflecting relative application rates. In contrast, estimates of total transport of each herbicide from the root zone, which varied in each quadrant and ranged from 0.06 to 2.3% for imazamethabenz-methyl plus imazamethabenz, 0.71 to 3.1% for imazethapyr, and 0.61 to 2.8% for imazamox, did not reflect application rates. In shallow ground water (piezometer samples), there was inconsistent and infrequent detection all four compounds. With the frequency and amount of rainfall typically encountered in the prairie region of Canada, contamination of shallow ground water with detectable concentrations of the three imidazolinone herbicides would be unlikely.
... Postemergence application of imazethapyr 75 g/ha is recommended for control of weeds in groundnut, but the choice of succeeding crops is limited because of its persistence in soil and plant for longer time with a half-life period of 33 months (Sondhia et al. 2015). However, persistence of imazethapyr depends upon soil type and its half-life which is 24 and 5 months in clay and sandy soils, respectively (Hollaway et al. 2006). There is need to evaluate alternate pre-and post-emergence herbicides for broad-spectrum weed control in groundnut and their residual effect on succeeding rotational crops. ...
... According to previous studies, imazethapyr hardly moves downward in the soil, even under conditions that favor leaching [9][10][11], with residues remaining in a layer of 10-20 cm in most soils [12,13] and being evenly distributed in the upper 15 cm [14,15]. Imazethapyr is strongly adsorbed to soil colloids at a low pH [16], and adsorption is positively correlated with organic matter content, clay content, and cation exchange capacity (CEC) [17][18][19][20][21][22][23][24][25][26][27][28]. Desorption hysteresis is more pronounced in higher pH soils [26,29,30]. ...
A bioassay study was conducted to determine the differences in the susceptibility of selected crops to simulated imazethapyr residues based on morphological and anatomical parameters. Sugar beet, white mustard, and rapeseed oil were found to be the most sensitive based on ED50 values for the root length and the root fresh weight. Corn and sunflower were less sensitive, and wheat was the least sensitive. The measured anatomical parameters confirmed the different sensitivities of the tested plants, as evidenced by a shortening of the meristem and elongation zones, a reduction in the distance between the root tip and the absorption zone, and the distance between the root tip and the point where the primordium of the lateral root appears. An imazethapyr residue level equivalent to ED20 (for root length) did not cause serious morphological changes in the less sensitive plants, nor did it cause significant changes in the length of the root cap, the beginning of the root absorption zone (root hair region), the beginning of lateral root formation (i.e., the permanent region), and the number of root primordia per root length. Therefore, ED20 could be proposed as an acceptable residue level (ARL) or herbicide residue level at which these plants can be safely sown.
... Loux et al. (1989) and Bresnahan et al. (2000Bresnahan et al. ( , 2002 also reported that IMR adsorption was strongly correlated with clay content which was responsible for longer persistence of these herbicides in clay loam soil. Hollaway et al. (2006) and Sondhia (2008) also reported that IMR has a rapid initial phase of degradation, followed by a slower second phase leading to long-term persistence especially in clay soil under field conditions and persistence of IMR was more affected by soil type rather than soil pH and microbial activities. ...
... It is phototoxic to succeeding crops like rapeseed, mustard, cabbage, sugar beet, potato and fibre flax (Cobucci et al. 1998;Bresnahan et al. 2002;Pannacci et al. 2006;Punia et al. 2011;Grichar et al. 2012). Previous studies have reported that imazamox is a persistent herbicide with DT 50 varying from 28 to 397 d under aerobic conditions depending upon temperature, soil texture, soil moisture, microbial activity and pH (Hollaway et al. 2004;Sondhia 2008). Anaerobic soil and aquatic metabolism studies have indicated that imazamox does not degrade under anaerobic conditions (DEPORS 2014). ...
As adsorption-desorption behavior of herbicide plays an important role in determining leachability, release rate and availability to target species, the present study aims to evaluate the influence of soil properties, temperature and ionic state of imazamox on its adsorption-desorption behaviour. The sorption was significantly influenced by above evaluated parameters and Freundlich adsorption coefficient varied from 0.24 х 10³ to 7.60 х 10³ mg1−1/n kg⁻¹ L1/n. In soils with pH in the range of 6.4 to 9.5, sorption of imazamox decreased with increase in solution pH while in acidic soil (pH 2.3 to 5.9) adsorption increased with increase in solution pH. At low solution pH adsorption occurs mainly through cationic form while at high solution pH adsorption was predominantly through anionic form. Presence of electrostatic attractive and repulsive forces, ∏→∏ charge transfer, hydrogen bonding and van der waals forces were key mechanisms affecting the adsorption of imazamox. Greater adsorption hysteresis was observed in soils having pH in the range of 6.2 to 9.5 suggesting relatively less adsorption and difficult desorption of imazamox in these soils. Due to irreversible binding in high pH soil, it can be speculated that it may enhance the chances of crop injury in these soils.
... Imazethapyr application resulted in greater control of docks than flumetsulam eight months after application. This finding is consistent with Hollaway et al. (2006) who found imazethapyr degraded more slowly than flumetsulam in the soil. They found 30% of applied imazethapyr present in the top soil layer after 10 months compared with flumetsulam, which was undetectable in some sites. ...
A field experiment was established in Lincoln, Canterbury in autumn 2018 to evaluate the effect of acetolactate synthase (ALS) inhibiting herbicides on subterraneun (sub) clover. Two herbicides, imazethapyr and flumetsulam, were applied to seven sub clover cultivars at the 4-5 trifoliate leaf stage during July 2018. By December 2018, both herbicides had reduced the broadleaf weed yield by 1000 kg DM/ha. Sub clover herbage yield in spring (3 Oct 2018) increased only for ‘Antas’ and ‘Napier’ cultivars but all cultivars had an increase in total annual herbage yield when herbicides were applied. Plots were managed for seed set so re-establishment was examined. Imazethapyr had a longer residual than flumetsulam with greater control of broad-leaved dock (Rumex obtusifolius) eight months after application. Herbicide application had no effect on subsequent sub clover emergence the following year. This experiment demonstrated the potential to establish a pure sward of sub clover with the use of ALS inhibiting herbicides, which could be used to create a high legume base in pasture before overdrilling grass the following year.
... These herbicides inhibits acetolactate synthase enzyme, which results in disruption of protein synthesis causing interference in cell growth and DNA synthesis leading to the death of plants (Cobucci et al., 1998;Sondhia, 2008). Previous studies have reported imazethapyr and imazamox as persistent herbicides with half-life varying from 7 to 513 days depending on temperature, soil texture, soil moisture, microbial activity and pH (Cobucci et al., 1998;Hollaway et al., 2004;Sondhia, 2008). These herbicides have differential sensitivity to succeeding crops such as sugarbeet, canola, raya, pea, spinach, barley and wheat (Cobucci et al., 1998;Bresnahan et al., 2002;Pannacci et al., 2006;Punia et al., 2011;Grichar et al., 2012). ...
Use of imazethapyr and imazamox has been an environmental concern due to their high persistence, water solubility, residue build up and potential to injure the succeeding crops. Hence, it is necessary to develop effective decontamination technology. In present study, effect of β-cyclodextrin-chitosan biocomposite (LCD) amendment in soil on dissipation of imazethapyr and imazamox and their phytotoxicity on succeeding crop was evaluated. The influence of different experimental variables viz. extractant solution and its concentration, liquid to soil ratio, amount of soil and soil type on dissipation of imazethapyr and imazamox was assessed through chemical assays. Irrespective of herbicide formulation and application rate, amendment of soils with LCD increased the dissipation rate of herbicide and the residues were below the detection limit (<0.005 μg g⁻¹) within 5 to 15 days in aridisol, entisol, inceptisol A, inceptisol B, inceptisol C and 7 to 21 days in alfisol and vertisol. Amendment of soils with LCD significantly reduced the growth inhibition of Brassica juncea (L.) Czern and improved the soil biological activity as evident from increase in dehydrogenase activity and soil bacterial count. Amendment of soils with LCD could be a promising, economically feasible and environmentally benign soil decontamination strategy for imazethapyr and imazamox contaminated soils.
... Loux et al. (1989) and Bresnahan et al. (2000Bresnahan et al. ( , 2002 also reported that IMR adsorption was strongly correlated with clay content which was responsible for longer persistence of these herbicides in clay loam soil. Hollaway et al. (2006) and Sondhia (2008) also reported that IMR has a rapid initial phase of degradation, followed by a slower second phase leading to long-term persistence especially in clay soil under field conditions and persistence of IMR was more affected by soil type rather than soil pH and microbial activities. ...
Imidazolinone group herbicides are known for longer persistence in soil. Therefore, a laboratory study was performed to evaluate the persistence of pre-mix formulation of two imidazolinone herbicides—imazethapyr and imazamox in clay and sandy loam soils. Herbicide formulation was applied at 70 and 140 g a.i. ha⁻¹ equivalent to recommended doses in legumes. For achieving efficient sample preparation, three methods namely ultrasonic-assisted extraction (UAE), matrix solid phase dispersion (MSPD), and solid phase extraction (SPE) were optimized. MSPD gave better recoveries (85.22 to 96.00%) over SPE (80.10 to 84.78%) and UAE (56.44 to 66.20%). Residues were estimated using gas chromatography tandem mass spectrometry (GC-MS/MS) which is previously not reported in open literature. Dissipation followed first-order kinetics and half-life period of 23.5 to 43.3 days in clay loam and 19.6 to 39.8 days in sandy loam soil. The results revealed the persistent nature of pre-mix formulation of both herbicides as only 64.2 to 86.6% residues dissipated after 90 days of application in both soils.
... Imazethapyr and its ready mix combination with imazamox, new herbicides of imidazolinone group have been found promising to control weeds in blackgram. Imazethapyr being highly persistent in soil may cause residual toxicity in succeeding crops (Hollaway et al. 2006). Keeping these in view, herbicides imazethapyr alone or in combination with imazamox and pendimethalin as pre-mixture were tested under pre and post-emergence conditions. ...
... Oilseed radish recovery in the Yu et al. (2015) study may be attributed to the slightly higher silt, clay, and cation exchange capacity compared with this study; temperature and rainfall were similar between their study and this study. Imazethapyr tends to persist more in soils with higher in clay and organic matter as it binds to clay and organic matter (Goetz et al. 1990;Hollaway et al. 2006); however, the persistence of imazethapyr contradicts the results obtained when comparing the two studies, as greater injury should have been seen in Yu et al. (2015). Higher clay content may also bind with imazethapyr, making it (Curran et al. 1991). ...
Residual herbicides can cause injury to a future crop. Residual herbicides applied to soybean [Glycine max (L.) Merr.] or winter wheat (Triticum aestivum L.) may impact cover crops seeded in the same growing season. The objective of this study was to determine the effect of residual herbicides on oilseed radish (Raphanus sativus L.) establishment and growth after 10 postemergence (POST) broadleaf herbicides were applied in winter wheat and 12 preemergence (PRE) and 7 POST herbicides were applied in soybean. Oilseed radish injury was assessed 14 and 28 d after emergence (DAE) and stand density and biomass were measured 28 DAE. Residual herbicides used for broadleaf weed control in winter wheat caused less than 5% oilseed radish visible injury and there was no reduction in stand density and biomass. In soybean, imazethapyr applied PRE caused 43% and 48% oilseed radish injury at 14 and 28 DAE, respectively. There was no decrease in oilseed radish stand density and biomass. Imazethapyr applied POST to soybean caused 47% and 59% oilseed radish injury at 14 and 28 DAE, respectively, and decreased oilseed radish biomass by 65%. There was no decrease in oilseed radish stand density. The results from this study conclude that many of the herbicides commonly used in winter wheat and soybean in Ontario do not negatively impact oilseed radish establishment and growth.
... The rate of degradation of imzaethapyr in soil is affected by a number of factors which include differential soil texture, pH, soil moisture, and temperature conditions. Hollaway et al. (2006) and Patel et al. (2009) reported that persistence of imazethapyr was more in clay soils than loam sandy soil. Bresnahan et al. (2000Bresnahan et al. ( , 2002 studied the effect of pH on the binding capacity of imazethapyr and observed that adsorption of imazethapyr increased with increase in pH. ...
... In our study, it was also found that the rainy days were up to 45 days after application of herbicides. Additionally, the observed biphasic pattern of degradation, i.e., initially rapid followed by a slower phase, supported the results of previous studies (Hollaway et al. 2006;Muñoz-Leoz et al. 2013). This can be attributed to increased sorption over time and growth of microorganisms being able to use imazethapyr as carbon source ( for as a fraction of the added herbicides was still in the dissolved phase and/or weakly adsorbed, Renner et al. 1988) and then become strongly adsorbed to clay and organic matter, thus resulting in lower bioavailability and slower degradation (Muñoz-Leoz et al. 2013). ...
A field experiment was conducted to examine the degradation and impact of two post-emergence herbicides (imazethapyr and quizalofop-p-ethyl) on soil ecosystems at a half recommended rate (HRE), recommended rate (RE), and double recommended rate (DRE) during kharif peanut cultivation. Herbicides were innocuous to soil microbial activity at HRE, however, showed some significant influences at RE and DRE, and exerted temporary toxic effects on microbial biomass carbon and fluorescein diacetate hydrolyzing activity. Dehydrogenase activity also declined for a shorter period except imazethapyr application at DRE. Acid phosphatase activity was inhibited whereas alkaline phosphatase activity fluctuated between promotion and inhibition, but promotion was predominant suggesting a direct role of alkaline soil environment. Soil NH4⁺ and NO3⁻ nitrogen were increased by the herbicides at initial (after 7 days) and last phases (after 30 days), respectively. After an early period of inhibition, urease activity returned to the control level after 30 days. Dissipation of imazethapyr residues fitted best to bi-exponential order rate kinetics at DRE and RE, whereas it followed first-order rate kinetics at HRE. The residues of quizalofop-p-ethyl were found only up to 1 day after application suggesting its rapid conversion to active acid metabolites. Both the herbicides had transient harmful effects on most of the soil microbiological parameters.
... Esses fatores influenciam diretamente a mobilidade do herbicida no perfil do solo, sendo este um aspecto importante na disponibilidade do herbicida para as plantas. Resultados de pesquisas demonstraram que, após um ano da aplicação de imazetapir, a maior concentração do herbicida foi observada até 20cm de profundidade em solo de várzea com 2,3% de matéria orgânica e 26% de argila (KRAEMER et al., 2009) ou 40cm após três anos de cultivos (HOLLAWAY et al., 2006). ...
The herbicides imazethapyr and imazapic, used in Clearfield® rice, have high mobility and persistence in the soil, causing injury to non-resistant rice grown in rotation. These herbicides can leach and reach greater depths along the profile. This positioning can be a in-depth selectivity factor and partially explain the different results found in literature about carryover of imidazolines. To understand this effect, this study had the objective of to evaluate the effect of the positioning of the mixture of imazethapyr and imazapic (75g ai L-1 and 25g ai L-1) on the injury to non-resistant rice crop. Two experiments were carried out in soil with 15% clay and 1.2% organic matter in a greenhouse at the Universidade Federal de Pelotas, Pelotas, RS, Brazil. Experiment I consisted of a preliminary study to verify the location depth of the herbicide in the soil profile that causes injury to rice non-tolerant rice, and the herbicides has been allocated at depths of 0, 5, 10, 20, 30, 50 e 70cm. Experiment II also consisted in the allocation of herbicide at depths in the soil profile of 3, 6, 9, 12, 15 and 18cm. The variables were visual plant injury, plant shoot dry weight and plant height. The formulated mixture of imazethapyr + imazapic located near the soil surface cause injury to non resistant rice plants but when allocated at depths greater than 20cm of the soil surface does not affect the development of non-resistant rice.
... The computation of adsorption coefficients K f produced low values ranging from 3.9x10 -5 to 114.4x10 -5 (Table 2) which indicates a weak sorption of imazethapyr by soil particles. This reflects high persistence for a long time in soils (Hollaway et al., 2006;Cessna et al., 2012), that can increase the potential carry over damage to non-target crops in rotations in subsequent year (Onofri et al., 1996). Moreover, it insinuates the contamination of the ground water through leaching process in a country experiencing physical water scarcity, and hence creates a threat to drinking water (Dabrowski et al., 2002). ...
Imazethapyr herbicide [5-ethyl-2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl) nicotinic acid] is widely used on agricultural field crops in Morocco. It is reported that soil properties largely enhance the sorption of the herbicide in soils, however understanding their impact in soils of Morocco is needed. The present article investigates the sorption behavior of imazethapyr herbicide toward six agricultural soils from Morocco in batch equilibrium experiments at pH 5; and evaluates the effect of the organic matter, the clay content, and the cation exchange capacity (CEC) on the sorption by applying simple and multiple linear regressions. Freundlich isotherm model described well the dynamic of imazethapyr sorption in all studied soils under the experimental conditions. The linear regressions showed significant differences between the soil properties on their impact on the sorption. While simple regression revealed strong positive correlations between the sorption and both the soil clay content (R2 = 0.91) and CEC (R2 = 0.92), the multiple regression revealed a noteworthy influence of soil organic matter when combined with clays. Our findings showed a weak adsorption of imazethapyr on the selected Moroccan soils, in addition to a potential role of clay minerals and CEC in the retention of the herbicide compared to the organic matter. The low adsorptive capacity of the Moroccan soils urges the necessity of minimizing herbicide application rates in agricultural regions to prevent environmental detrimental impacts.
... The concentration of imazethapyr slowly decreased over the incubation time of 120 d. Imazethapyr degradation was initially rapid, but was followed by a slower phase, which was consistent with the results of previous studies (Hollaway et al. 2006). The imazethapyr concentration was larger in the HS soil than the QL soil for all incubation times. ...
Large amounts of imazethapyr were applied for weed control in cultivation fields in China, but their effects on the soil microbial community remains unclear. In this study, two agricultural soils, a silty loam (HS) and a loamy soil (QL), were spiked with imazethapyr (CK, 0.1, 1 and 10 mg kg(-1)) and incubated for 1, 15, 30, 60, 90 and 120 d. In addition, untreated controls received only water. The soil microbial community structures were characterized by investigating the phospholipid fatty acids (PLFA) and microbial biomass C. Soil microbial biomass C and total concentration of PLFA were variable with incubation time, which were also reduced by the addition of imazethapyr. Imazethapyr addition also decreased the ratios of GN/GP and fungi/bacteria. A larger stress level, measured as the ratio of PLFA (cyc17:0+cyc19:0)/(16:1ω7c+18:1ω7c), was found in the high concentration (1 and 10 mg kg(-1)) herbicide treatment groups. The effects of imazethapyr at the field application on soil microbial biomass and microbial community were minor. Principal component analysis (PCA) of the PLFA clearly separated the treatments and incubation times. Both soils showed different total PLFA concentrations and ratios of GN/GP and fungi/bacteria, but similar changes in the PLFA pattern upon soil treatment. The soil microbial community structure was shifted by the addition of imazethapyr, which recovered after 60d. In addition, the dissipation of imazethapyr was slow in both soils. Our results demonstrated that the addition of imazethapyr shifted the microbial community structure, but that it recovered after a period of incubation.
... [5] [6] There is some evidence that imidazolinone herbicides may persist and affect growth of succeeding crops under certain conditions. [7] Hollaway et al. [8] reported ...
The abiotic degradation of the imidazolinone herbicides imazapyr, imazethapyr and imazaquin was investigated under controlled conditions. Hydrolysis, where it occurred, and photodegradation both followed first-order kinetics for all herbicides. There was no hydrolysis of any of the herbicides in buffer solutions at pH 3 or pH 7; however, slow hydrolysis occurred at pH 9. Estimated half-lives for the three herbicides in solution in the dark were 6.5, 9.2 and 9.6 months for imazaquin, imazethapyr and imazapyr, respectively. Degradation of the herbicides in the light was considerably more rapid than in the dark with half lives for the three herbicides of 1.8, 9.8 and 9.1 days for imazaquin, imazethapyr and imazapyr, respectively. The presence of humic acids in the solution reduced the rate of photodegradation for all three herbicides, with higher concentrations of humic acids generally having greater effect. Photodegradation of imazethapyr was the least sensitive to humic acids. The enantioselectivity of photodegradation was investigated using imazaquin, with photodegradation occurring at the same rate for both enantiomers. Abiotic degradation of imidazolinone herbicides on the soil surface only occurred in the presence of light. The rate of degradation for all herbicides was slower than in solution, with half-lives of 15.3, 24.6 and 30.9 days for imazaquin, imazethapyr and imazapyr, respectively. Abiotic degradation of these herbicides is likely to be slow in the environment and is only likely to occur in clear water or on the soil surface.
Simazine is one of triazine herbicides that may leave residual activity in the soil for extended periods causing injury and yield reduction of susceptible crops in rotation. An experiment was conducted in order to study the sensitivity of crops to simazine soil residue. Experimental type was completely randomized design in a factorial arrangement with three replications. Treatments included crops (rapeseed and barley) and simazine simulated concentrations re siduals in soil (0.0032, 0.016, 0.032, 0.064, 0.096 and 0.16 mg. kg-1soil). Results showed that the shoot and root dry matter were significantly affected by increasing simazine soil residue in all crops (p<0.01), but seed emergence was not affected. Crops showed different response to simazine soil residues. Based on ED50 parameter rapeseed (0.0091 mg.kg-1soil) and barley (0.0202 mg.kg-1soil) appeared the most sensitive and tolerant crops to simazine soil residue, respectively.
The dynamic and residues of florasulam and flumetsulam in corn field ecosystem were investigated using quick, easy, cheap, effective, rugged, and safe (QuEChERS) procedure with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The limits of quantification (LOQs) of the proposed method ranged from 0.005 to 0.01 mg/kg. Mean recoveries and relative standard deviations (RSDs) of the two compounds in all samples at three spiking levels ranged 94-110 % and 2.0-9.2 %, respectively. Florasulam and flumetsulam degradation followed first-order kinetics with half-lives 1.7-2.9 and 3.3-8.7 days in soil and 1.3-1.8 and 0.9-1.7 days in plant, respectively. The residues in all the samples were found to be less than the LOQs at preharvest intervals of 53 and 78 days. The results suggest that the combined use of florasulam and flumetsulam on corn is considered to be safe under the recommended conditions and can be utilized for establishing the maximum residue limit (MRL) of florasulam in corn in China.
A determinação da concentração de compostos no solo por meio de plantas quantificadoras apresenta como principal vantagem detectar somente resíduos biologicamente ativos, não havendo necessidade de instrumentos onerosos e de prévia extração dos resíduos do solo. Dessa forma, este trabalho teve como objetivo selecionar plantas quantificadoras da presença de herbicidas residuais (pré emergentes) para o uso em bioensaios. Utilizou-se delineamento experimental completamente casualizado com arranjo bifatorial 8 x 6, com cinco repetições. O fator A consistiu de espécies cultiváveis e o fator B de herbicidas aplicados em pré emergência. Os resultados evidenciaram que a sensibilidade na detecção do herbicida no solo depende da espécie utilizada. A sensibilidade das espécies Lactuca sativa L. e Raphanus sativus var. sativus L. não permitiu condições de quantificar a presença dos herbicidas atrazina, cloransulam, imazaquin, metribuzin e S-metolacloro. Raphanus sativus var. oleiferus Metzger é potencial quantificador de imazaquin e S metolacloro. Plantas de Curcubita pepo L. são promissoras na bioavaliação de metribuzin. A espécie Cucumis sativus L. mostrou-se potencial bioindicadora de cloransulan e imazaquin. Avena sativa L. apresentou-se como potencial quantificadora de imazaquin e metribuzin. Hordeum vulgare L. pode quantificar o metribuzin e Triticum aestivum L. é promissor na detecção da biodisponibilidade de atrazina. PALAVRAS-CHAVE: BIOENSAIO; CINÉTICA DE DISSIPAÇÃO; MEIA-VIDA; HERBICIDAS.
In the present paper the results of some studies on the synthesis of some new derivatives of sulfonamidated aryloxyalkylcarboxylic acids obtained by the condensation of their hydrazides with several substrata affording final compounds with potential biological activities such as anti-tumour, anti-oxidative, anti-tubercular as well as fungide, acaricide and plant growth regulating actions are reported. The synthesis stages of the new products (azomethines and diazoaminoderivatives) are presented as well as the elemental analysis data and IR, 'H-NMR spectral measurements aimed to elucidate the chemical structures while the anti-microbial properties were confirmed by microbiological tests. The anti-microbial activity was estimated by measuring the growth inhibition area for four different strains of microorganisms: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Candida albicans. The tests performed have confirmed the potential biological properties of the newly obtained compounds.
Five new aryloxyalkylcarboxylic acid derivatives (diazoaminoderivatives) are studied for their thermal behavior by applying a coupled TG-FTIR technique over the (30-400 oC) range in correlation with the environmental impact of gaseous species resulting by thermal degradation. These compounds are of a particular practical significance since they show a high biological potential as agrochemicals, such as pesticides (herbicides, acaricides, fungicides, growing stimulators etc.). This is why the paper follows the evaluation of the environmental impact of the gaseous species evolved by thermal degradation of the compounds under study when the processing temperature of the products retaining these compounds is exceeded above the initial degradation temperature. The evaluation of the impact on the environment - air (EIA) gave results corresponding to a real situation of a modified air for which the index of global pollution ( ) is estimated.
Imazethapyr has been widely used in Rio Grande do Sul since the development of Clearfield TechnologyTM(CL) on rice, in a formulated mixture of imazethapyr + imazapic (75 + 25g L-1). However, the use of such technology raised the problem of herbicide carryover, which might affect non-tolerant crops in rotation with different intensities. The plant injury is related, among other factors, with the herbicide position in the soil profile. The present work had the objective of determining the depth positioning of imazethapyr on a lowland soil cultivated with rice in two soil tillage system: conventional system (CS) and no till system (NT), in an area where CL rice had been cultivated for two years followed by non tolerant rice in the third year. Herbicide concentration in soil samples was analyzed by HPLC-DAD. There is a higher concentration of imazethapyr in the topsoil (0-5cm) on the CS, when compared to the NT, while it leached until 20cm in both systems. In the CS, imazethapyr were uniformly distributed in the first 15 cm of soil, whereas in NT, imazethapyr were accumulated in 5-10 and 10-15cm layers.
Grain growers in south-eastern Australia have reported unexpected crop failures with theoretically safe recropping periods for acetolactate synthase herbicides in alkaline soils. This experience has led to the concern that these herbicides may degrade very slowly in alkaline soils, and herbicide residues have at times been blamed for unexplained crop losses. To address this issue, we established 5 recropping trials across Victoria and South Australia with 5 acetolactate synthase herbicides (chlorsulfuron, triasulfuron, metsulfuron-methyl, imazethapyr, and flumetsulam). The herbicides were applied to separate plots in years 1, 2 or 3, and sensitive crop species were sown in year 4 to measure the impact of herbicide residues. We observed that the persistence of the sulfonylureas (chlorsulfuron, triasulfuron, metsulfuron-methyl) varied between herbicides, but all persisted longer in alkaline soils than in acid soils, and were, therefore, more likely to damage crops in alkaline soil. Imazethapyr persisted longer in clay soils than in sandy soils and was, therefore, more likely to damage crops in clay soils. All herbicides persisted longer when rainfall was below average. Canola was more sensitive to imazethapyr than either pea, lentil or medic, but was less sensitive to the sulfonylureas. In contrast, lentil and medic were the most sensitive to sulfonylureas. Despite some damage, we found that safe recropping periods could be predicted from the product labels in all but one situation. The sole exception was that metsulfuron-methyl reduced dry matter and yield of lentil and medic sown 10 months after application in a soil with pH 8.5. We hypothesise that the real cause of crop failure in many situations is not unusual herbicide persistence, but failure to take full account of soil type (pH and clay content including variation in the paddock) and rainfall when deciding to recrop after using acetolactate synthase herbicides.
The TG-FTIR analysis of some new diazoaminoderivatives is aimed to follow the structure-thermal stability-degradation mechanism correlation. The TG–DTG–DTA curves are indicative of a complex and specific mechanism of thermal degradation in air of the diazoaminoderivatives under study which show a common characteristic regarding their degradation in air (30–900°C) when two domains in function of temperature (time) can be noticed: an endothermic one, identical to the degradation under nitrogen atmosphere, and an exothermal one. The gaseous species resulting by degradation are also grouped in these domains.The identification by means of the specific absorbances of every gaseous species and those obtained by TG-FTIR revealed that N2, NH3, H2CNH, SO2, H2O, CO2, C4H8, C3H4 are eliminated within the first domain while SO2, H2O, CO2 within the second. These results afforded the most probable thermal degradation mechanism to be advanced.Since these compounds could show practical importance as initiators (generators of free radicals) and also as biologically active substances, their thermal stability and the degradation mechanism can give significant information on the temperature range proper for their practical application. Besides the compounds released by thermal degradation could give information about the potential environmental pollution.
The article is devoted to a comparative study on the thermal degradation of some new diazoaminoderivatives under both air
and nitrogen atmosphere by TG-FTIR analysis. The TG–DTG–DTA curves show the thermal degradation in air to present two temperature
domains: an endothermic one identical to the case of the degradation under nitrogen and an exothermic one which is not to
be found under nitrogen atmosphere. The identification of the gaseous species released by degradation in air within the endothermic
domain made evident the presence of the same components of the degradation in nitrogen atmosphere. In the exothermic domain
of the sample degradation in air, the CO2, H2O, SO2 species result by the burning of the molecular residues of the first domain. The obtained results afforded a degradation
mechanism to be advanced that coincide for the endothermic domain with that of degradation under nitrogen atmosphere. Due
to the importance of these compounds as possible reaction initiators and also as potentially bioactive substances (herbicides,
acaricides, fungicides), the study on their thermal degradation could give useful information on the environmental impact
of the degradation products resulting by the thermal processing of the plants which could possible retain these compounds,
when the initial degradation temperature is exceeded.
The study on the thermal behavior of some new diazoaminoderivatives was aimed to follow the structure-thermal stability-degradation
mechanism correlation by means of the TG-FTIR technique and formation enthalpies. The TG-DTG-DTA curves reveal the thermal
degradation in air (30–900 °C) to show two ranges as a function of temperature (time), where the gaseous species resulting
by degradation are eliminated: the first, an endothermic one which is identical to that under nitrogen atmosphere and the
second, an exothermal one. As made evident by the identification of the individual gaseous species by their characteristic
absorbances as well as those obtained by TG-FTIR the compounds C2H2, H2C = NH, SO2, NH3, CO2, H2O, HCl are eliminated in the first domain while CO2, SO2, H2O in the second, which afforded the advancement of the most probable degradation mechanism.
A determinação da concentração de compostos no solo por meio de plantas quantificadoras apresenta como principal vantagem detectar somente resíduos biologicamente ativos, não havendo necessidade de instrumentos onerosos e de prévia extração dos resíduos do solo. Dessa forma, este trabalho teve como objetivo selecionar plantas quantificadoras da presença de herbicidas residuais (pré emergentes) para o uso em bioensaios. Utilizou-se delineamento experimental completamente casualizado com arranjo bifatorial 8 x 6, com cinco repetições. O fator A consistiu de espécies cultiváveis e o fator B de herbicidas aplicados em pré emergência. Os resultados evidenciaram que a sensibilidade na detecção do herbicida no solo depende da espécie utilizada. A sensibilidade das espécies Lactuca sativa L. e Raphanus sativus var. sativus L. não permitiu condições de quantificar a presença dos herbicidas atrazina, cloransulam, imazaquin, metribuzin e S-metolacloro. Raphanus sativus var. oleiferus Metzger é potencial quantificador de imazaquin e S metolacloro. Plantas de Curcubita pepo L. são promissoras na bioavaliação de metribuzin. A espécie Cucumis sativus L. mostrou-se potencial bioindicadora de cloransulan e imazaquin. Avena sativa L. apresentou-se como potencial quantificadora de imazaquin e metribuzin. Hordeum vulgare L. pode quantificar o metribuzin e Triticum aestivum L. é promissor na detecção da biodisponibilidade de atrazina.
The disappearance of imazethapyr from soil solution was investigated to evaluate transport in undisturbed soil columns. Soil treated with imazethapyr was incubated for 0.15, 1, 2, 4, 8, and 16 d, at which times soil solution was obtained by vacuum displacement. The classical convective-dispersive equation was used to describe solute transport through undisturbed soil columns. Bromide and imazethapyr breakthrough curves (BTCs) were indicative of preferential solute mobility. Imazethapyr BTCs were similar to model simulation using transport parameters determined from Br- BTCs. Preferential flow paths apparently reduced attenuation of imazethapyr as predicted from equilibrium adsorption measurements. -from Authors
One of the most commonly used techniques to assess the efficacy of herbicides is to apply to the principle of bioassays. A bioassay is defined as an experiment for estimating the potency of a herbicide by analysis of the reaction that follows its application to living organisms. The analysis of variance is central to most applications of statistical methods in the analysis of experiments. This is true for bioassay, but perhaps the fundamental importance of regression and related concepts is here particularly apparent. The purpose of this presentation is to quantify herbicidal effects of applying non‐linear regression models to herbicide bioassays, and to demonstrate how some general hypotheses about the mode of action of the assayed herbicides can be incorporated into the regression models. The validity of herbicide bioassay data is discussed in view of the general principles used in bioassay in other biological sciences.
Research was conducted in 1994 and 1995 to evaluate the field mobility of flumetsulam in three soils of varied texture and organic matter content but constant pH (pH = 6.0 ± 0.1). Flumetsulam was monitored to a depth of 122 cm at 28, 56, and 84 days after treatment (DAT). Flumetsulam concentrations were determined by cotton bioassay, with separate standard curves for various soil-depth combinations. Following a preemergence application of flumetsulam at 224 g ai ha-1, the herbicide was primarily limited to the upper 8 cm of soil, regardless of soil type, year, or DAT. Exceptions to this typically occurred following substantial rainfall amounts early in the season. Beyond 28 DAT, no significant concentrations of flumetsulam were detected below 15 cm. Results from this research suggest that leaching is not a significant route of flumetsulam dissipation in the field.
Laboratory studies were conducted to evaluate flumetsulam adsorption and mobility in seven Mississippi soils of different organic matter content, pH, and texture. Adsorption isotherms were determined for all soils using a 1:1 (soil:water) technique. In six of seven soils, Freundlich n constants were close to unity, suggesting a partitioning-like adsorption mechanism for flumetsulam. Mobility was examined using packed soil columns. 14C-flumetsulam recoveries in leachate ranged from 1 to 70% and were influenced by both organic matter content and soil pH. However, the effects of organic matter content and soil pH were not independent. Consequently, clear relationships between flumetsulam mobility and either organic matter content or soil pH were not established across all soils. However, among soils of similar pH (7.5 ± 0.3), mobility decreased linearly (R2 = 0.75) as organic matter content increased from 0.7 to 3.6%. Across soils with similar organic matter content (3.9 ± 0.3%), mobility increased linearly (R2 = 0.98) as soil pH increased from 5.3 to 7.2. Net adsorption constants (K(d)) provided a more accurate assessment of flumetsulam mobility across all soils than K(oc).
Laboratory studies were conducted to evaluate 14C-flumetsulam mobility in two Mississippi soils of varied texture and organic matter content following delays in irrigation. Mobility was evaluated using packed soil columns, 25 cm deep, under unsaturated-saturated flow conditions. Irrigation timings included 0, 3, and 5 d after flumetsulam application. Flumetsulam mobility (defined as the amount collected in leachate) decreased from 45% to no more than 20% of the applied in the Prentiss sandy loam soil when irrigation was delayed 3 or 5 d. With the Okolona soil, flumetsulam recovery in the leachate was 21, 14, and 6%, respectively when irrigation occurred 0, 3, and 5 d after application. Flumetsulam proved to be mobile when irrigation immediately followed application, with 6 to 45% recovered in the leachate from all soils evaluated. The Prentiss soil retained 6% of the applied flumetsulam in the upper 5 cm and the Okolona soil retained 22% when irrigation immediately followed flumetsulam application. When the irrigation interval was delayed at least 3 d, the Okolona soil retained 40% in the upper 5 cm, whereas the Prentiss soil retained 10%. Flumetsulam mobility was dependent on irrigation timing and soil type.
The volatilization, photolysis, microbial degradation, and field persistence of imazethapyr were studied using formulated and ¹⁴ C-labeled imazethapyr. Volatilization losses from soil were less than 2%. Photodecomposition losses of up to 8% occurred from soil and up to 52% from a glass slide with no soil. Significantly greater photodecomposition occurred with chain-labeled than ring-labeled ¹⁴ C-imazethapyr. The amount of ¹⁴ CO 2 evolution from soil treated with either ring- or chain-labeled ¹⁴ C-imazethapyr was not significantly different. The total ¹⁴ CO 2 evolved from the soils ranged from 2.4 to 3.6% of the total ¹⁴ C-imazethapyr applied to the soil. However, degradation of imazethapyr from the same soils, as determined by high-pressure liquid chromatography, indicated that 62 to 82% of the applied ¹⁴ C-imazethapyr had been degraded. The degradation rate increased as soil moisture was increased from −100 to −33 kPa. Imazethapyr was more persistent in soil with the higher clay and organic matter content.
Use of imidazolinone herbicides has often resulted in carryover effects on sensitive rotational crops. The effect of soil residues of imazethapyr and imazamox on several vegetable crops grown in rotation with soybean (Glycine max [L.] Merr.) was investigated over a 5-yr period in southern Ontario. Imazethapyr at 0, 100 and 200 g a.i. ha -1 was applied preemergence to soybean from 1991 to 1993. Imazethapyr at 0 and 100 g a.i. ha -1 and imazamox at 35 g a.i. ha -1 was applied postemergence to soybean in 1994 and 1995. Cabbage (Brassica oleracea L.), potato (Solanum tuberosum L.), tomato (Lycopersicon esculentum L.), sweet corn (Zea mays L.) and cucumber (Cucumis sativus L.) were planted each spring, 1 and 2 yr following preemergence imazethapyr application and 1 yr following postemergence imazethapyr and imazamox application. Potato and sweet corn showed visual injury symptoms 1 yr after preemergence imazethapyr application in 2 of 3 yr while cabbage, tomato and cucumber showed visual injury symptoms all 3 yr. Minor visual injury symptoms did not reduce yields. Cabbage was the most sensitive to imazethapyr soil residues. Cabbage yields were reduced in 2 of 3 yr, due to carryover residues from 100 and 200 g ha -1 of imazethapyr applied the previous year. Tomato and potato also showed yield reductions in 2 of 3 yr due to imazethapyr soil residues. The degree of injury and yield reduction was influenced by soil pH and soil moisture. There were no yield reductions for any crop 2 yr after imazethapyr application. Imazamox soil residues were less injurious than imazethapyr soil residues to vegetable crops grown in rotation and resulted in only minor visual injury symptoms and no yield reductions on tomato, potato or cabbage.
The extent of ¹â´C-imazaquin and ¹â´C-imazethapyr abiotic vs biotic degradation in soil was investigated. Degradation was measured in an in vitro system which allowed 90% recovery of applied herbicide. Triallate biodegradation is well documented and therefore used as a standard. Herbicide degradation was compared in two soils, a Cisne silt loam and a Drummer silty clay loam. Herbicide degradation in gamma-irradiated soil was compared to fresh soil. Biomass quantities were measured for the duration of the experiments. ¹â´COâ evolution, extractable parent, metabolites, and unextractable residue were measured. After 12 weeks of incubation, 95% of the radioactivity could be extracted as parent from sterilized soil. In unsterilized soil, imazaquin and imazethapyr degraded at a similar rate which was dependent upon soil type. All herbicides degraded slower in the Drummer soil and triallate degraded two to three times faster than the imidazolinones in either soil. ¹â´C-imazaquin degradation products included ¹â´COâ and unextractable residues. The major product from ¹â´C-imazethapyr degradation was ¹â´COâ. Evolution of ¹â´COâ from an imazethapyr-treated Cisne soil, containing a serial dilution of activated charcoal, demonstrated that adsorption of herbicide was negatively correlated with degradation. Therefore imidazolinone microbial degradation is regulated by the amount of herbicide in soil solution as determined by soil characteristics.
SummaryA bioassay method using the radicles of pea (Pisum sativum L.) and lupin (Lupinus angustifolius L.) was developed for the assessment of trials on herbicides of common use in the sulfonylurea class (chlorsulfuron, triasulfuron and metsulfuron-methyl) and in the sulfonanylide class (flumetsulam and metosulam). Soils within a range of pH 5.8–8.4 with textures from sand to clay were used in these experiments. The sensitivities of the species were similar in chlorsulfuron and flumetsulam trials and their response range varied with soil type and herbicide, e.g. between 0.75 and 6.0 ng triasulfuron g−1 in the Wimmera grey clay and between 0.125 and 8.0 ng chlorsulfuron g−1 soil in the Mallee sand. The method was demonstrated in a wide range of uses, encompassing tests of the initial bioactivity of formulations of chlorsulfuron and flumetsulam, monitoring the field leaching and persistence of triasulfuron and measuring relative potencies between the classes, using metsulfuron-methyl and metosulam. The bioassay response provided a high level of reproducibility and precision, which was measurable by the logistic curve-fitting procedure. In each case, R2 values were >0.90 and lack-of-fit tests were clearly non-significant at the 0.05 level. Chi-square tests were used to measure differences between ED50's. The method does not require the pre-germination and selection of seedlings, daily watering or root-washing and results are obtained 7 days from sowing, providing favourable use for routine analyses and large-scale trials.
Sulfonylurea (SU), sulfonamide (SA), and imidazolinone (IMI) herbicides are relatively new classes of chemical compounds that function by inhibiting the action of a plant enzyme, stopping plant growth, and eventually killing the plant. These compounds generally have low mammalian toxicity, but plants demonstrate a wide range in sensitivity to SUs, SAs, and IMIs with over a 10,000-fold difference in observed toxicity levels for some compounds. SUs, SAs, and IMIs are applied either pre- or post-emergence to crops commonly at 1/50th or less of the rate of other herbicides. Little is known about their occurrence, fate, or transport in surface water or ground water in the USA. To obtain information on the occurrence of SU, SA, and IMI herbicides in the Midwestern United States, 212 water samples were collected from 75 surface-water and 25 ground-water sites in 1998. These samples were analyzed for 16 SU, SA and IMI herbicides by USGS Methods Research and Development Program staff using high-performance liquid chromatography/mass spectrometry. Samples were also analyzed for 47 pesticides or pesticide degradation products. At least one of the 16 SUs, SAs or IMIs was detected above the method reporting limit (MRL) of 0.01 microg/l in 83% of 130 stream samples. Imazethapyr was detected most frequently (71% of samples) followed by flumetsulam (63% of samples) and nicosulfuron (52% of samples). The sum of SU, SA and IMI concentrations exceeded 0.5 microg/l in less than 10% of stream samples. Acetochlor, alachlor, atrazine, cyanazine and metolachlor were all detected in 90% or more of 129 stream samples. The sum of the concentration of these five herbicides exceeded 50 microg/l in approximately 10% of stream samples. At least one SU, SA, or IMI herbicide was detected above the MRL in 24% of 25 ground-water samples and 86% of seven reservoir samples.