This study was developed based on a goosegrass (Eleusine indica (L.) Gaertn) population with resistance to multiple modes of action of herbicides (EPSPs inhibition - glyphosate; and ACCase inhibition - aryloxyphenoxypropionate chemical group), from Primavera do Leste, MT, Brazil. The objective was to identify possible mechanisms of resistance associated or not to sites of action of herbicides. Several experiments and analyses were carried out with the contribution of different laboratories and institutions. The results obtained allowed to conclude that: (i) the mutation Asp2078Gly conferred resistance to ACCase inhibitors, without overexpression of ACCase or changes in herbicide absorption and translocation; (ii) overexpression of EPSPs, mutations Thr102 and P106, and changes in absorption and translocation are not involved in the E. indica resistance to glyphosate; (iii) the metabolism of glyphosate in resistant E. indica plants requires further studies to elucidate the herbicide final destination in these plants. The mechanism of resistance of E. indica biotypes to ACCase-inhibiting herbicides was elucidated: it involves a change in the action site. However, the mechanism of resistance to EPSPs-inhibiting was not conclusive, denoting that some hypotheses should be tested, mainly regarding the metabolism of glyphosate in resistant plants.
Chloris elata is an important weed for grain and sugarcane crops. In addition to its aggressiveness, it may show resistance to glyphosate herbicide. In this context, the aim of this study was to assess the effectiveness of glyphosate formulations, isolated or in association with ACCase inhibitors, in controlling C. elata (putatively resistant to glyphosate) at different developmental stages. Four experiments were conducted in a completely randomized design. Treatments consisted of glyphosate application under different formulations with ACCase inhibitors, isolated or in mixtures. Applications were carried out at the stages of four fully expanded leaves in Experiment I, four tillers in Experiment II, and at regrowth of the four-tiller plants in Experiments III and IV. Applications of glyphosate isopropylamine salt associated with sethoxydim or clethodim showed to be among the best treatments in Experiments I, II, and III, presenting control scores equal to or greater than 90%. However, not even these treatments could provide successful control in Experiment IV. Moreover, and regardless of the formulation, isolated glyphosate, showed 85% (Experiment III) and 50% (Experiment IV) maximum controls. Associations between glyphosate and ACCase-inhibiting herbicides showed to be effective in controlling C. elata, especially at early developmental stages. In general, isolated herbicides provided lower percentages of control, as well as higher values of dry matter. Sole herbicide applications were not effective in controlling C. elata (putatively resistant to glyphosate), regardless of the developmental stage. Highlights: Mixtures between glyphosate and ACCase-inhibiting have been shown to be effective in C. elata control, especially in the early development stages. Isolated herbicide applications were not effective in controlling C. elata, regardless of the development stage. Mixtures between glyphosate and ACCase-inhibiting is more important in the control than the glyphosate formulation or ACCase-inhibiting used.
Glyphosate, glufosinate, and atrazine do not affect the growth and development of glyphosate and glufosinate-tolerant (RR2/LL) maize; however, the results are less consolidated for these herbicides applied in mixtures. The aim of the present study was to evaluate the effects of post-emergent application of glyphosate, glufosinate, and atrazine, alone and in mixtures, on the growth and development of the RR2/LL maize. The treatments consisted of the application of glyphosate (1080 g of acid equivalent [ae] ha-1), glufosinate (500 g of active ingredient [ai] ha-1), atrazine (2000 g [ai] ha-1), glyphosate + glufosinate, glyphosate + atrazine, glufosinate + atrazine, glyphosate + glufosinate + atrazine, and the control (without application). The experiment was carried out in two locations under greenhouse conditions with different maize hybrids. Crop injury and variables of the agronomic performance (height, stem diameter, chlorophyll indexes, fresh and dry weight of shoot, root dry weight, and total dry weight) were evaluated. Herbicides applied alone or in binary mixtures did not cause major damage. However, the application of the three associated herbicides in some situations might result in detrimental effects on the development of the RR2/LL maize.
use for selective post-emergence control of glyphosate-resistant Conyza spp. in black oats. Adv Weed Sci. 2021:e20210026.
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