RESUMO
Lake Tota (Boyaca, Colombia) supplies water for human consumption, agriculture and industry for more than 500.000 people. Oxadixyl and Tebuconazole are fungicides used in onion crops in the lake catchment area. The mobility of pesticides in soil, bioavailability and transfer to other environmental compartments depend on sorption and desorption kinetics and mechanisms. An understanding of these processes is essential for transport modeling and the rational design of corrective measures against pollution. A displacement study was performed on a hand packed soil column in laboratory conditions. A pulse of 0,01 M CaCl2 solution, containing a tracer (Bromide) and the fungicides Oxadixyl y Tebuconazole, was injected. Column experiment was performed at 0.078 cmh(-1) flow rate under unsaturated conditions. Eluates were collected in flasks at constant intervals and the volumes of eluate were recorded. After rainfall simulation, the soil from the column was sliced into six successive sections (5 cm). Methanol extraction was used to determine the fungicide in each soil section. Samples were measured by HPLC. Only Oxadixyl was recovered in leachates. Unlike bromide breakthrough curve, Oxadixyl was asymmetrical, with early breakthrough and increased tailing. The percentage eluted was 96.7% after ten pore volumes. Tebuconazole showed the highest retention in the first five cm of soil layer. The results suggest that oxadyxil presents highs risk to leachate through the soil profile and that Tebuconazole is strongly absorbed in Colombian soil.
Assuntos
Acetamidas/química , Fungicidas Industriais/química , Oxazóis/química , Triazóis/química , Poluentes Químicos da Água/química , Colômbia , Monitoramento AmbientalRESUMO
Lolium multiflorum (Italian ryegrass) has recently demonstrated itself to be poorly controlled with glyphosate in cereal crops of South Chile. The concentration of glyphosate necessary to reduce shoot length by 50% (ED50) in seedlings, after eight days of root contact was 7.3-fold in the resistant Vil-1 than in the susceptible (S) biotype. The obtained spray retention values were higher on S than the resistant (Vil-1) biotype. Contact angles measured on the adaxial surface of S and Vil-1 were similar. However, on the abaxial surface contact angles were of 63 degrees on Vil-1 as compared to 42 degrees on S. A greater glyphosate uptake was observed through the abaxial surface of S. Regarding translocation, glyphosate accumulated mainly in the tip of the treated leaf of Vil-1, 24 h after treatment. It was afterwards also well distributed to the rest of the leaves and roots, as in the susceptible biotype. Nevertheless, 14C-glyphosate remained higher in the foliar apex of Vil-1. Hence, resistance to glyphosate by the Vil-1 Lolium multflorum biotype seems to involve a lower uptake through the abaxial leaf surface and a different migration pattern.
Assuntos
Resistência a Medicamentos , Glicina/análogos & derivados , Herbicidas/farmacologia , Lolium/efeitos dos fármacos , Adaptação Fisiológica , Bioensaio , Glicina/farmacologia , Concentração Inibidora 50 , Lolium/crescimento & desenvolvimento , Controle de Pragas/métodos , GlifosatoRESUMO
The effect of weeds on the diminution of agricultural production is considered to be between 30 and 50%. Imazethapyr is a herbicide which acts on the enzyme ALS, the first common enzyme in the biosynthetic pathway of valine, leucine and isoleucine. Euphorbia heterophylla is a common species in soybean fields in Brazil and different populations resistant to herbicides of the sulfonylurea and imidazolinone groups are currently being reported. The objectives of this work were: to determine the resistance of three different biotypes named RI, RII and RII to the herbicide imazethapyr: to establish the level of resistance to this herbicide, and to evaluate the behaviour of the biotypes to other herbicides with a similar mode of action. The response of plants treated with imazethapyr confirmed the existence of resistance in the biotypes denominated as RI, RII and RIII. The imazethapyr concentration required to reduce the activity of the enzyme ALS by 50% (I50) should be greater than 500 microM for biotypes RI, RII and RIII and 39.47 microM for the susceptible biotype. Applications made in the greenhouse at field doses of ALS inhibiting herbicides showed cross resistance in the case of imazamox and imazamethabenz but not in the cases of the other ALS inhibitor herbicides used. ALS activity results demonstrated that the imazethaphyr resistance in different biotypes of E. heterophylla is target site mediated.
Assuntos
Euphorbia/efeitos dos fármacos , Herbicidas/toxicidade , Ácidos Nicotínicos/toxicidade , Brasil , Resistência a Medicamentos , Imunidade Inata , Doenças das Plantas/microbiologia , Glycine max/microbiologiaRESUMO
APPs (aryloxyphenoxypropionates) and CHDs (cyclohexanediones) are two of the most important groups used post-emergence for the control of grass weeds. They inhibit the lipid synthesis in plants by interfering with the activity of the enzyme Acetyl-coenzyme A carboxylase (ACCase), acting at a meristematic level. The resistance patterns of the biotypes characterized seem to indicate the existence of different degrees of resistance. It is thus possible to identify biotypes presenting cross-resistance only to certain APPs, to APPs and CHDs, or only to CHDs. The objective of this work was to evaluate the cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, propaquizafop, cyhalofop-butyl, haloxyfop-R-methyl, tralkoxydim and tepraloxydim in three species of Lolium (L. multiflorum, L. perenne, and L. rigidum) resistant to diclofop-methyl. The assays were conducted with petri-dishes in which, over increasing doses, fifty seeds per biotype and dose were located in each dish. Two weeks later, the following parameters were evaluated: germination (%), number of roots, radicle length, plumule length, and fresh weight reduction (%). Based on plumule length and fresh weight reduction (%), diclofop-methyl resistant biotypes showed cross-resistance to fenoxaprop-P-ethyl, fluazifop-P-butyl, cyhalofop-butyl, haloxyfop-R-methyl, but not to propaquizafop, tralkoxydim and tepraloxydim. The parameters germination (%), number of roots or root length did not show a good relation between the dose and its efficacy (curves of dose response) for any of the susceptible and resistant biotypes studied.