Amaranthus hybridus is a C4 broadleaf species widely spread across Brazilian agricultural territory. Recently, several herbicide resistance reports have been documented in southern Brazil, including the reports for enolpyruvilshikymate-3-phosphate (EPSPS)-and acetolactate-synthase (ALS)-inhibitors. The objective of this study was to confirm the existence of an ALS resistant (R) A. hybridus population from Paraná state. Dose-response experiments were conducted with R and a known susceptible (S) population with herbicides from three different chemical groups of ALS inhibitors. Biomass relative to untreated control was quantified and GR 50 (dose for 50% of biomass reduction), GR 90 (dose for 90% of biomass reduction) and resistant index (RI) were calculated based on non-linear regression analysis. The R population was 6.9-fold resistant to chlorimuron-ethyl and 6.5-fold resistant to metsulfuron-ethyl (sulfonylureas -SUL). Additionally, the recommended rates from each herbicide was not sufficient to reach 90% control to R based on GR 90 parameter estimation. There was no resistance to imazethapyr (imidazolinone -IMI) and cloransulan-methyl (triazolopyrimidine -TRI) due to the low doses of GR 90 and non-significant RIs. The R A. hybridus population investigated was resistant to ALS inhibitors chlorimuron-ethyl and metsulfuron-ethyl (SUL), but susceptible to IMI and TRI herbicides.
The objective of this work was to evaluate potential management strategies for control cotton stalks using herbicide treatments associated to mowing. The experiment was conducted in the field from August to December 2013, installed at the end of the development cycle of the cotton crop in a factorial scheme (28x2) with subplots, in a randomized complete block design with four replications (one or two sequential application). The factor analyzed in the plot was constituted by herbicide treatments and the factor analyzed in the subplots was the number of applications of the treatments after the mechanical control. The evaluated variables were the percentage of visual control, the number of regrown plants and the size average of the regrowth. Only one application of the herbicide treatments did not promote satisfactory control of the cotton stalks. The treatments with 2,4-D + glyphosate + saflufenacil + [imazapic + imazapyr], glyphosate + saflufenacil + fluroxypyr and glyphosate + dicamba + saflufenacil, promoted total control of the cotton stalks (100%) at 21 days after sequential application and did not present regrowth plants until the last evaluation date, and were, therefore, the most efficient treatments to control cotton stalks.
Knowledge on weed biology and ecology is fundamental to provide suitable control practices in weed management systems. The objective of this research was to understand the effect of light and temperature on germination of Chamaesyce hirta, as well as to evaluate the effect of depth of seed placement in the soil in the emergence of the plant. Two experiments were conducted. In the first one, in the laboratory, the seeds were placed to germinate in plastic boxes and kept in a B.O.D. germination chamber, under constant temperatures of 20, 25, 30 and 35 ºC, either in the dark or under continuous light. Daily germination assessments were performed. The percentage of germinated seeds in the 10-day period and the germination speed index (GSI) were calculated. In the second trial, carried out in greenhouse conditions, 100 seeds were planted, under six levels of seeding depth (0, 1, 2, 3, 4 and 5 cm) and three soil cover conditions: no straw, under black oats (Avena strigosa) straw and under corn (Zea mays) straw. Daily plant emergence was counted along 30 days and total emergence and GSI were calculated. Germination of C. hirta seeds occurs both in the presence and absence of light. For the highest temperature, both increased germination and GSI were reported in the presence of light. The highest levels of emergence were obtained with the absence of plant cover and under corn straw at 0 cm depth. The presence of black oat straw on the soil reduced the emergence of C. hirta.
Glyphosate has been widely used to control greater beggarticks populations that are resistant to acetolactate synthase (ALS) inhibitors in South America. However, herbicide control failures has been observed over the last three growing seasons in grain production areas of Paraguay. In this research, we report the first case of multiple resistance to glyphosate (EPSPs) and imazethapyr (ALS) in greater beggarticks (Bidens subalternans) population from Paraguay. This conclusion was supported by dose-response experiments conducted in two consecutive years (2018 and 2019) with a putative resistant (R) and a susceptible (S) population. Alternative herbicides were also tested for post-emergence control of R population. For glyphosate, the resistant factor (RF) values were 8.8- (2018) and 15.7-fold (2019). For imazethapyr, the RF values were 59- and 58-fold, in 2018 and 2019, respectively. Treatments with 2,4-D, dicamba, 2,4-D + glyphosate, dicamba + glyphosate, lactofen, fomesafen, ammonium-glufosinate, atrazine, and bentazon provided more than 80% control of the R population. This is the first case of multiple resistance to glyphosate and imazethapyr in greater beggarticks (Bidens subalternans) in the world. The mechanisms underlying resistance in this biotype should be evaluated in future research.
RESUMO - A inoculação das sementes com Azospirillum spp. é uma prática que tem sido rotineiramente realizada no milho, sobretudo via formulação líquida. Todavia, as respostas relativas a outros modos de inoculação com diferentes formulações são, ainda, pouco conhecidas. Desta forma, objetivou-se com este trabalho avaliar a eficiência agronômica de doses de A. brasilense em formulação polimérica em pó, aplicada diretamente na caixa semeadora, sobre os componentes da produtividade do milho. Para tanto, foi conduzido um ensaio em blocos casualisados, com quatro repetições. Os tratamentos consistiram de uma testemunha, dose total de N, ½ dose de N; ½ dose de N + inoculação comercial padrão e ½ dose de N + quatro doses de inoculante em pó (1, 2, 4 e 8 g kg-1), aplicado na caixa semeadora. Foram avaliados os caracteres produtividade, números de fileira por espiga e de grãos por fileira, massa de mil grãos, matéria seca da parte aérea e teores de N nos grãos e na parte aérea. Nas condições testadas, a dose de 2 g kg-1 de sementes do inoculante, quando associada à adubação nitrogenada de 90 kg ha-1, apresentou superioridade no rendimento da cultura, ultrapassando, inclusive, a inoculação comercial com produto líquido.Palavras-chave: Zea mays, fixação biológica, inoculante, rendimento. MAIZE YIELD IN RESPONSE TO THE APLICATION OF Azospirillum spp. INTO THE SEED TANK ABSTRACT - Seed inoculation with Azospirillum spp. is a practice that has been routinely carried out in maize crop, especially via liquid formulation. However, responses concerning other methods of inoculation of different formulations are still poorly understood. The objective of this work was to evaluate the agronomic efficiency of the application of powder formulation of Azospirillum brasilense directly into the sowing box. For this purpose, a randomized block trial with 4 replications was carried out. The treatments tested consisted of absence of N fertilizer, the full N recommendation and a combination of the half of recommended N associated with the inoculation of four doses of A. brasilense (1, 2, 4 and 8 g kg-1) in powder formulation. The following variables were evaluated: number of kernel per row, number of row per ear, shoot dry biomass, thousand seed weight, grain N content, shoot N content and grain yield. All treatments submitted to inoculation with the powder formulation showed higher yields than the treatment in which the total dose of N was applied. However, superior results were obtained for the treatment in which ½ dose of N was associated with the powder inoculant in the proportion of 2 g kg-1 of seed.Keywords: Zea mays, biological fixation, inoculant, productivity.
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