S.L.O. Machado

Monitoring of the herbicide clomazone in environmental water samples by solid-phase extraction and high-performance liquid chromatography with ultraviolet detection

SummaryEvaluation of a simple and rapid method for determination of clomazone in environmental water samples, by high-performance liquid chromatography with ultraviolet detection, is described. After solid-phase extraction with C18 extraction cartridges clomazone was separated on a C18 column with 65∶35 (v/v) methanol-water, pH 4.0, as mobile phase at a flow-rate of 1.0 mL min−1. After optimization of the extraction and separation conditions, the method was used for determination of clomazone residues in rivers and agricultural waters of the central region of the Rio Grande do Sul province. The results revealed that clomazone persists in agricultural water at least for 130 days, and was present in 90% of the river water samples analyzed.

Arroz tolerante a imidazolinonas: controle do arroz-vermelho, fluxo gênico e efeito residual do herbicida em culturas sucessoras não-tolerantes

After several decades searching for tools to control red rice, imidazolinone tolerant rice was developed to selectively control red rice. To better understand this technology An experiment was conducted in 2004/2005, in Santa Maria, Rio Grande do Sul, Brazil to evaluate: 1) red rice control by imidazolinone herbicides in Clearfield™ rice; 2) evaluate the imidazolinone herbicide carryover effect on rygrass and non-tolerant rice (IRGA 417) and 3) evaluate the outcrossing rates between Clearfield rice and red rice. The experimental design was a randomized block design, with 3 treatments and 12 replications. To determine the outcrossing rates between Clearfield rice and red rice, virtually all the red rice panicle was collected and analyzed in the area. The carryover effect was tested using ryegrass and a non-tolerant rice cultivar (IRGA 417). The herbicides tested controlled red rice. Although injury to Clearfield rice was observed, the herbicide did not affect yield. Herbicide carry-over to non-tolerant rice was observed, reducing plant stand on rice seeded 361 days after herbicide application. Natural out-crossing occurred between Clearfield rice and red rice, at rates of 0.065%.

Risk assessment of surface water contamination by herbicide residues: monitoring of propanil degradation in irrigated rice field waters using HPLC-UV and confirmation by GC-MS

This study evaluates the degradation of the herbicide propanil and of its major degradation product, 3,4-dichloroaniline (3,4-DCA) in water from irrigated rice farming in the State of Rio Grande do Sul, Brazil. It also assesses the contamination risk of surrounding surface waters. After a solid phase extraction step, the concentration of both compounds was determined by high performance liquid chromatography with ultraviolet detection. Confirmation was conducted by gas chromatography-mass spectrometry. Concentrations of propanil in water samples varied from 0.1 to 3600 µg L-1. Propanil was degraded very rapidly to 3,4-DCA and high concentrations of this product were found, varying from 1.0 to 567.5 µg L-1 in water. The obtained half-life times for propanil in water under real conditions for the 2001, 2002 and 2003 harvests were 18.2, 12.5 and 12.2 h, respectively.

Destino ambiental dos herbicidas do grupo das imidazolinonas: revisão

The herbicides of the imidazolinone group control a wide range of weed species. They are absorbed by weed roots and leaves and transported through the phloem and xylem, accumulating in the plant growing points. They inhibit the enzyme acetolactate synthase (ALS), which synthesizes the branched chain amino acids. When used in the field, a large portion of these herbicides reach the soil, where they can be absorbed by the roots of plants, sorbed into the soil colloids, or dissolved in soil solution, going through photolysis, hydrolysis, microbial degradation or leaching. The sorption of imidazolinone is faster and affects other processes. High contents of clay, organic matter and pH lower than 6.0 contribute to enhance the sorption and persistence of imidazolinones in soil. The most important way of dissipation is by microbial degradation, thus conditions favoring microbial development will also enhance imidazolinone degradation.

Study of the Degradation of the Herbicide Clomazone in Distilled and in Irrigated Rice Field Waters using HPLC-DAD and GC-MS

This study evaluated the degradation of the herbicide clomazone in distilled water and from irrigated rice fields, through UV irradiation and under natural conditions. After a solid phase extraction (SPE) as preconcentration step, the remained concentration of clomazone was determined by high performance liquid chromatography with diode array detection (HPLC-DAD) and the identification of the degradation products was achieved by gas chromatography-mass spectrometry (GC-MS). Under UV irradiation, the clomazone was degraded faster in distilled water than in surface water. In irrigated rice water, under sunlight irradiation, clomazone presented a half-life time average of 3.2 days in three consecutive harvests, and after application the concentration in water remained higher than 0.1 μg L-1 for 20 days. Several by-products, like 2-chlorobenzaldehyde and 2-chlorobenzene methanol, were identified by GC-MS, which evidenced that the concentration of intermediates at the begining increase and then they also undergo degradation.

Controle de arroz-vermelho em dois genótipos de arroz (Oryza sativa) tolerantes a herbicidas do grupo das imidazolinonas

Red rice (Oryza spp.) is one of the main limiting factors to rice (O. sativa) yield. An experiment was carried out to evaluate red rice control and the behavior of two rice genotypes tolerant to the imidazolinone herbicides in response to imazethapyr (75 g L-1 ) + imazapic (25 g L1 ) application rates and timing. The experiment was conducted in Santa Maria-RS, Brazil in 2004/2005 and was arranged in a factorial scheme, in a randomized block design, with four replications. Factor A included the two rice genotypes tolerant to the imidazolinones, a cultivar (IRGA 422 CL) and a hybrid (Tuno CL); and factor D included the treatments for red rice control, which was a combination of rates and herbicide application timing. The hybrid was found to be more tolerant to the herbicide only than the cultivar. Application rates up to 200% on the hybrid genotype could be done without affecting rice yield. It is important to state that increasing the rate of herbicide application can create carryover problems to non-tolerant crops. Red rice control was total with split application of imazethapyr + imazapic in PRE and POST emergence with the total rate above 125%. The most efficient treatment was application of 75% in PRE followed by 50% in POST, which was the lowest rate promoting 100% control, with relatively low toxicity to the cultivar and without affecting rice yield.

Persistence of the herbicides imazethapyr and imazapic in irrigated rice soil

The mixture of herbicides imazethapyr and imazapic is used to control red rice in irrigated rice crops. However, such herbicides might persist on the soil for a long period causing phytotoxicity on susceptible rice grown in succession. The objective of this work was to determine the effect of different soil tillage systems during the off-season on the residual phytotoxicity of imazethapyr and imazapic on non tolerant rice. Herbicide residues caused phytotoxicity on susceptible rice with the highest values being registered 25 days after emergence and decreasing after this period until almost disappearing 60 days after emergence. Herbicide residues affected plant stand, number of stems per m2, number of panicles per m2 and plant height, but did not affect grain yield. Soil movement decreased herbicide activity on the superficial soil layer (0-3 cm).

Controle químico de arroz-vermelho na cultura do arroz irrigado

Red rice (Oryza spp.) reduces rice (Oryza sativa L.) grain yield and quality. A field study was conducted to compare two red rice control tools, the first using the Clearfield™ system and the second using high rates of clomazone and rice seeds treated with safener to suppress red rice emergence. The treatments included: check control without herbicide application, three treatments for the formulated herbicide mixture (imazethapyr 75 g i.a. L-1 + imazapic 25 g i.a. L-1) under the Clearfield system, and three clomazone treatments (clomazone 500 g i.a. L-1). The most efficient treatment for red rice control was the formulated mixture of imazethapyr + imazapic (0.7 L ha-1 PRE followed by 0.7 L ha-1 POST). This treatment promoted 100% red rice control, without affecting plant stand and promoting high grain yield.

Carryover of Imazethapyr and Imazapic to Nontolerant Rice

Abstract The present work aimed to evaluate plant injury caused by residues in the soil of the formulated mixture of imazethapyr and imazapic to a nontolerant genotype of rice (IRGA 417) drilled at 371 and 705 d after herbicide application (DAA). Herbicide carryover reduced up to 55% of the grain yield of the IRGA 417 drilled at 371 DAA, and plant injury was still evident at 705 DAA but without grain yield reduction. Nomenclature: Imazethapyr; imazapic; rice, Oryza sativa L. ‘IRGA 417’

Imazethapyr and imazapic, bispyribac-sodium and penoxsulam: zooplankton and dissipation in subtropical rice paddy water.

Herbicides are very effective at eliminating weed and are largely used in rice paddy around the world, playing a fundamental role in maximizing yield. Therefore, considering the flooded environment of rice paddies, it is necessary to understand the side effects on non-target species. Field experiment studies were carried out during two rice growing seasons in order to address how the commonly-used herbicides imazethapyr and imazapic, bispyribac-sodium and penoxsulam, used at recommended dosage, affect water quality and the non-target zooplankton community using outdoor rice field microcosm set-up. The shortest (4.9 days) and longest (12.2 days) herbicide half-life mean, estimated of the dissipation rate (k) is shown for imazethapyr and bispyribac-sodium, respectively. Some water quality parameters (pH, conductivity, hardness, BOD5, boron, potassium, magnesium, phosphorus and chlorides) achieved slightly higher values at the herbicide treatment. Zooplankton community usually quickly recovered from the tested herbicide impact. Generally, herbicides led to an increase of cladocera, copepods and nauplius population, while rotifer population decreased, with recovery at the end of the experiment (88 days after herbicide treatment).