Chemical control of Cyperus rotundus in pre and post emergent application Controle químico de Cyperus rotundus em aplicaçao pré e pós- emergente

Objective: the objective of this work was to test potential herbicides, tested in a single dose of each commercial product as indicated in the package insert. Materials and Methods: the experiment was carried out in two trials, preand post-emergent, in a completely randomized block design with eight treatments and three replications in an 8x3 factorial scheme. The test was carried out in a BOD oven at 25o and 12 hours/light photoperiod in sand beds containing sedge rhizomes, visual evaluations were performed 7 and 14 days after herbicide application, in both tests, followed by a tretrazolium test at the end. of visual evaluation in tubers that did not germinate, thirty days after pre-emergent application. Results: the most efficient control was the herbicide of the Organoarsenic group (MSMA) which presented 0.67% of viable rhizomes in the pre-emergent assay and 0.33% of viable rhizomes in the postemergent assay. Conclusion: the herbicide of the organoarsenic chemical group (MSMA) was the most efficient for the control of nutsedge in both trials. The herbicides ethoxysulforan and glyphosate showed control efficiency in the post-emergence assay.


Introduction
Cyperus rotundus L. (Cyperaceae), known in Brazil as tiririca, is considered the most widespread and aggressive weed in the world 1 .
The sedge is one of the most difficult weeds to control worldwide and also the one that causes the most damage in agricultural cultivation areas 2 . In Brazil, it grows substantially in a few days if subjected to favorable soil and climatic conditions, in soils of excellent agricultural aptitude, it can spread at an alarming level of 3000 tubers per m² in which up to 2000 plants can emerge 3 .
The adequacy of post-emergence herbicide application to the stage of maximum susceptibility is fundamental for the success in the control of nutsedge. It is important that the leaf area is sufficient for good retention and absorption of the spray applied 4 . There is a need to know the ability of the herbicide to act at the vital point after reaching the plant, directly on the leaves, or indirectly, by entering the soil solution, a herbicide that eliminates tubers of this weed will present better results in pre-emergent application 3 . Other studies have been carried out in order to seek the most appropriate management for this weed, as in the studies by 5,6 in which these authors seek to reduce the impacts of the growth of this plant in agricultural crops.
Due to the rapid ability to show resistance to herbicides, many commercial products are no longer effective in controlling sedge. This study aimed to evaluate the effectiveness of chemical control of the sedge Cyperus rotundus with pre-emergence and post-emergence treatment, with different commercial products available on the market.

Materials and Methods
Two experiments were set up (one with pre-emergent treatment of the tuber and the other with post-emergence of the tuber) in a controlled environment in a BOD-type greenhouse, adopting a completely randomized block experimental design, with eight treatments and three replications, conducted in a sand bed. (gerbox), containing ten healthy tubers of defined mass collected in a crop area, placed in a BOD-type oven at 25º C and 12 hours of photoperiod.
In both tests, 250 mL of spray volume were prepared for each treatment and 75 mL were applied in each repetition. For unit transformations, the spray volume per hectare indicated on the package insert of each product was used.
The germination was evaluated daily and after 15 days of the treatments application, the tuber mass of each repetition were evaluated and the treatments that did not germinate were submitted in the pre-emergent test to the tetrazolium test in an aqueous solution of 0.1% of the salt of Trazolium. They were conditioned in BOD at 30° for 1.5 hours to determine their viability, being considered viable those that stained pink.

Results
In the pre-emergent treatment of tubers, it was observed 15 days after sowing that there was no germination of nutsedge tubers in any of the herbicides tested (Graph 1).
Graph 1 -Percentage of seedling tubers germination in pre-emergent treatment with herbicides.
When the treatment was post-emergent of the bulbs, it was observed that the efficiency of the active principles was lower in controlling the sedge (Graph 2).   (Table 1).
In this experiment, there was no significant result for the pre-emergent test, where the rhizomes remained viable, as shown by the tetrazolium test (Table 1), but in the post-emergent test the result was effective in controlling the nutsedge. We can observe the results obtained through the pre-emergent and post-emergent tests Glyphosate is, therefore, a post-emergent herbicide, which cannot be used as a pre-emergent, as it undergoes strong adsorption to soil particles and, therefore, does not act on plants, as observed in the tetrazolium test (Table 1). Considered a non-selective herbicide for its broad aspect, it has In this experiment, there was no significant result for the pre-emergent test with ethoxysulforan, where the rhizomes remained viable, as shown by the tetrazolium test (Table 1) There were no significant results in both pre-emergence and post-emergence tests with the tested herbicide from the tembotrione group, these herbicides act as inhibitors of the synthesis of 4hydroxyphenylpyruvate dioxygenase (4-HPPD).
It is considered that herbicides of this group act in a general way in some enzymatic sites of the route of synthesis of carotenoid pigments. Blocking the synthesis of these pigments is the phenomenon responsible for the appearance of the characteristic symptom of "albinism" or depigmentation. HPPD inhibitor, enzyme that acts in the synthesis of plastoquinone, enzyme cofactor of the carotenoid synthesis pathway (PDS) and integrant of the electron flow of photosynthesis 13 .
However, this process may not inhibit chlorophyll synthesis, which may explain the low efficiency of these products 9,14 , as well as the rapid metabolism of some plants in relation to these products. Products, not producing toxic metabolites capable of producing an effect on nutsedge.
The test with the herbicide of the Aryloxyphenoxypropionic Acids group that acts as inhibitors of lipid synthesis, did not present significant results in the effective chemical control both in the pre-emergence test and in the post-emergence test, it is known that this herbicide acts from the first reaction in the metabolic route of lipid synthesis involves the carboxylation of acetyl coenzyme A (Acetyl-CoA), mediated by the enzyme Acetyl-Coa carboxylase (ACCase). ACCase These herbicides inhibit the production of lipids, but alone they may not be enough to kill the plant 9 , describe reports of weed resistance to this active ingredient, as well as the need to use adjuvants to increase absorption and translocation in the plant.
The herbicide that showed the highest efficiency in this experiment in both tests was from the organoarsenic group (MSMA) as shown in the tetrazolium test (Table 1), this herbicide has an unknown mechanism of action, since the sites of action of these herbicides are not known , it is possible that they present differences in the mechanism of action between them and in relation to the other groups, with MSMA being the only Brazilian herbicide registered with this mechanism of action 9 .
These herbicides are described as post-emergent, since their absorption occurs in the foliar form, thus being considered a contact product. Widely used in association with hormonal herbicides as a desiccant 9 .
Another point to be highlighted is the effect of the substance Organoarsenic (MSMA), which, regardless of the form of treatment, proved to be highly effective on the viability of sedge bulbs, as in the study carried out 6 , where this herbicide showed efficiency in reducing the viability of tubers.

Conclusion
It was concluded that the herbicide of the organoarsenic chemical group (MSMA) was the most efficient for the control of nutsedge in both trials. The herbicides ethoxysulforan and glyphosate showed control efficiency in the post-emergence assay.

Authors' contribution
All authors have approved the final version of the manuscript and declared themselves to be responsible for all aspects of the work, including ensuring its accuracy and integrity.