Elephant grass (Pennisetum purpureum Schum.) is an important forage crop that has been proposed as a potential feedstock for bioenergy production. However, weed interference is a major factor limiting elephant grass production. Field experiments were conducted in 2014 and 2015 to evaluate preemergence herbicides for selective weed control in an elephant grass pasture. Herbicide treatments included atrazine + S-metolachlor, atrazine + simazine, ametryn, ethoxysulfuron, S-metolachlor, diuron + hexazinone, sulfentrazone, imazethapyr, and atrazine at label use rates. Weedy and weed-free treatments were included. Atrazine + S-metolachlor, atrazine + simazine, ametryn, ethoxysulfuron, S-metolachlor, sulfentrazone, and atrazine did not cause phytotoxicity on elephantgrass 35 days after treatment (DAT). However, diuron + hexazinone and imazethapyr were the most phytotoxic on elephantgrass, resulting in 81 and 70% phytotoxicity in 2014, and 7 and 6% phytotoxicity in 2015 respectively 35 DAT. All treatments provided effective weed control (>81%) with the exception of ethoxysulfuron (0 and 11% in 2014 and 2015, respectively), and atrazine (59% in 2014). These results show that atrazine + S-metolachlor, atrazine + simazine, ametryn, ethoxysulfuron, S-metolachlor, sulfentrazone, and atrazine were selectives when applied in preemergence in elephant grass pasture.Index terms: Bioenergy; biofuel; napier grass; forage; Pennisetum purpureum. RESUMOO capim-elefante (Pennisetum purpureum Schum.) é uma planta forrageira importante que tem sido proposta como matéria-prima potencial para a produção de bioenergia. No entanto, a interferência das plantas daninhas é um fator limitante na produção do capim-elefante. Experimentos de campo foram realizados em 2014 e 2015 para avaliar herbicidas aplicados em condições de pré-emergência para o controle seletivo de plantas daninhas em pastagem de capim-elefante. Os tratamentos herbicidas incluíram atrazine + S-metolachlor, atrazine + simazine, ametryn, ethoxysulfuron, S-metolachlor, diuron + hexazinone, sulfentrazone, imazethapyr e atrazine em doses normalmente recomendadas no rótulo. Foram incluídas as testemunhas sem capina e capinadas. Atrazine + S-metolachlor, atrazine + simazine, ametryn, ethoxysulfuron, S-metolachlor, sulfentrazone e atrazine não causaram fitotoxicidade em capim-elefante aos 35 dias após os tratamentos (DAT). No entanto, diuron + hexazinone e imazethapyr foram os mais fitotóxicos ao capim-elefante, resultando em 81 e 70% de fitotoxicidade em 2014, e 7 e 6% em 2015, aos 35 DAT, respectivamente. Todos os tratamentos de controle de plantas daninhas foram eficazes (> 81%) com a exceção de ethoxysulfuron (0 e

The interference imposed by weeds is one of the most important factors limiting elephant grass forage yield. Two experiments were carried out in 2015/2016 and 2017 to evaluate the selectivity and weed control of 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicides applied alone or in combination with atrazine in elephant grass. The treatments applied in the experiment conducted in Valença, Rio de Janeiro State, Brazil, were as follows: two rates of mesotrione (0.072 and 0.144 kg ha -1 + 0.5% v/v mineral oil -Assist®), two rates of tembotrione (0.075 and 0.100 kg ha -1 + 0.5% v/v mineral oil -Aureo®), atrazine + mesotrione (1.25 + 0.072 kg ha -1 + 0.5% v/v mineral oil -Assist®), atrazine + tembotrione (1.25 + 0.100 kg ha -1 + 0.5% v/v mineral oil -Aureo®), atrazine + mesotrione (1.25 + 0.072 kg ha -1 ), atrazine + tembotrione (1.25 + 0.100 kg ha -1 ) and two checks (weed-free check and weedy check). The same herbicide treatments and a check without application were applied in an experiment conducted in Coronel Pacheco, Minas Gerais State, Brazil. Two application rates of mesotrione with the addition of mineral oil or the tank mixture of atrazine plus mesotrione, with or without the addition of mineral oil, did not provide injuries capable to reduce elephant grass forage yield. Tembotrione was phytotoxic to elephant grass when applied with mineral oil. Atrazine plus tembotrione in a tank-mix, with or without mineral oil, were also phytotoxic to elephant grass. All treatments provided satisfactory weed control.

Elephant grass (Pennisetum purpureum Schum.) fodder productivity and quality are directly affected by weed interference. The difficulty in controlling weed species is one of the major limitations to the production and use of elephant grass as a forage crop in dairy farming and biomass for energy production. In this study, field experiments were conducted in 2014 and 2015 at two locations in Minas Gerais State, Brazil, to evaluate the tolerance of elephant grass pasture to acetolactate synthase inhibitor herbicides. The experimental pastures were treated at 1× and 2× the normal field-use rates (g ai ha -1 ) with metsulfuron-methyl (7.8 and 15.6), chlorimuron-ethyl (15 and 30), halosulfuron (112.5 and 225), ethoxysulfuron (150 and 300), and nicosulfuron (60 and 120). A nontreated control was also included. The results showed that metsulfuron-methyl, chlorimuron-ethyl, halosulfuron, and ethoxysulfuron caused mild injury symptoms on elephant grass plants, but did not reduce forage biomass production. Nicosulfuron caused considerable percentage injury to the plants, which varied from 53% to 73% and from 65% to 83% for the lower and higher rates, respectively. Elephant grass was tolerant of metsulfuron-methyl, chlorimuron-ethyl, halosulfuron, and ethoxysulfuron. Therefore, these herbicides could potentially control weeds in elephant grass fields.