Jethro Barros Osipe

Residual activity of herbicides applied to the soil in relation to control of four Amaranthus Species

Herbicides applied at pre-emergence normally present residual activity in the soil, controlling the first weed germinations, and preventing initial weed competition. The aim of this study was to determine the period of residual activity provided by sufficient herbicide rates for 95% (C95) control of the species Amaranthus hybridus, A. lividus, A. spinosus and A. viridis, and to assess the recommended rates of these herbicides. The study was conducted under greenhouse conditions in soils of sandy clay loam texture (20% clay and 1.9 of organic matter, with rates of alachlor, diuron, oxyfluorfen, pendimethalin, prometryne, oxyfluorfen, S-metolachlor, trifluralin 450 and trifluralin 600 being applied at 30, 20, 10 and 0 days before weed sowing. Weed control was evaluated after herbicide permanence in soil for 0, 10, 20 and 30 days after application (DAA). The residual activity of alachlor and prometryne at a rate C95 was not sufficient for the efficient control (>80%) of the species for up to 30 DAA. For alachlor, the use of the recommended rate did not provide considerable increase in residual activity, except for A. viridis. The recommended rate of prometryn promoted efficient control of the species for up to 30 DAA, except for A. hybridus. The recommended rate of oxyfluorfen provided an efficient control of A. hybridus and A. spinosus up to 30 DAA. These species had not been effectively controlled by the rate C95. Trifluralin 450 promoted efficient residual control for up to 30 DAA only compared with A. hybridus. Trifluralin 600 was effective in controlling A. hybridus and A. viridis up to 30 DAA and 29 and 28 DAA for A. lividus and A. spinosus, respectively. Clomazone did not promote efficient control of the species for 30 DAA, except for A. viridis. Diuron, pendimethalin and S-metolachlor were effective in controlling the species for up to 30 DAA, at both rates, showing consistent residual activity for the soil studied.

Identificação e controle de biótipos resistentes de Digitaria insularis (L.) Fedde ao glyphosate

Some invasive species has shown potential to develop resistance to glyphosate herbicide in no-till areas. Herbicides inhibitors of ACCase enzyme may be an alternative control to Digitaria insularis (L.) Fedde. The objectives of this study were to identify the occurrence of resistance in D. insularis (L.) Fedde to glyphosate in tillage areas of the State of Parana, and find the appropriate clethodim doses for its control. Were conducted two experiments in a greenhouse in Bandeirantes-PR, where the first was the experiment conducted with the glyphosate herbicide and the second with clethodim herbicide. Seeds of D. insularis (L.) Fedde plants were collected from five different places, and dose response curves were obtained for resistance verification. The tested doses were equivalent to 0; 0.5; 1; 2; 3 and 4 times the recommended dose of herbicide. The plants had 15 to 20 cm high when the herbicides were sprayed. The results showed that D. insularis (L.) Fedde biotypes from Parana cities are resistant to glyphosate herbicide. Furthermore, it was found differentiated tolerance to the clethodim herbicide in the biotypes.

Aplicações isoladas ou associadas de diuron, oxyfluorfen e prometryne para o controle de Euphorbia heterophylla

Pre-emergence herbicide application at the beginning of the crop cycle is a consecrated practice among cotton farmers. Although herbicides, such as diuron, oxyfluorfen and prometryn, are options for this crop, not much is known about their effect on Euphorbia heterophylla. This work aimed to elaborate dose-response curves for diuron, oxyfluorfen and prometryn in relation to E. heterophylla control, as well as to provide biological efficiency data for tank mixtures of these herbicides. Thus, six experiments were simultaneously carried out under greenhouse conditions, with three consisting of increasing doses of each herbicide applied isolated and three of tank mixtures of two herbicides. The dose-response curve was adjusted for % of biomass reduction at 28 days after application; I80 and I95 (respectively dose for 80% and 95% of weed control and biomass reduction), were also determined. Diuron, oxyfluorfen and prometryn applied alone were effective within the range of the doses evaluated to control E. heterophylla. In general, tank mixtures containing oxyfluorfen were considered additive or antagonistic, while tank mixtures of diuron + prometryn were additive or synergistic. Out of the three possible combinations evaluated, oxyfluorfen + prometryn resulted in the smallest number of combinations promoting acceptable control of wild poinsettia.

SPECTRUM OF WEED CONTROL WITH 2,4-D AND DICAMBA HERBICIDES ASSOCIATED TO GLYPHOSATE OR NOT

ABSTRACT The possibility of using auxin mimics herbicides in culture postemergence applications contributes to weed management. This study aimed at evaluating and comparing the effectiveness of 2,4-D and dicamba herbicides on glyphosate resistant or tolerant weeds. The treatments were dicamba and 2,4-D doses with or without glyphosate. The evaluated weeds in the experiment were Richardia brasiliensis, Commelina benghalensis, Conyza sp. and Ipomoea nil. Herbicides were applied when weeds were in 4 to 6 and 10 to 12 leaves stages. Data referring to evaluations on day 30 after application were submitted to analysis of variance. Response-dose curves were obtained for herbicides, and C85 and C95 values were identified. Weed species showed different tolerance to dicamba and 2,4-D, and differences were more evident for C. benghalensis. The addition of glyphosate to the auxin mimic reduced the differences between them. For plants in less developed stages, regardless of the species, mixtures of glyphosate + 2,4-D or glyphosate + dicamba provided excellent levels of control. In general, considering equivalent doses, for R. brasiliensis, C. benghalensis and I. nil, 2,4-D herbicide was superior to dicamba. As for Conyza bonariensis, dicamba showed better control percentages.