Abstract: Background: Echinochloa colona (junglerice), a troublesome weed in rice, is resistant to 15 herbicide active ingredients. High temperatures are linked to reduction of herbicide efficacy. Objective: Evaluate growth and seed production of junglerice, after five generations of recurrent selection with sublethal dose of rice herbicides under heat stress. Methods: Junglerice plants previously subjected to recurrent selection with herbicides and heat stress for three cycles were exposed to further iterative cycles of selection with heat stress (45 °C) and sublethal dose of florpyrauxifen-benzyl (FPB, 0.125x), imazethapyr (0.125x), quinclorac (0.25x), and glufosinate (0.25x). Plant injury was evaluated 1 and 3 weeks after treatment. Panicle number; plant height; and dry biomass of shoot, panicles, and seeds were recorded. Seed number plant-1 and reproductive effort were estimated. Results: The joint effect of heat stress and sublethal dose of herbicides reduced the sensitivity of junglerice to all herbicides tested. Plants treated with FPB and quinclorac produced more shoot biomass and seed number after five generations. Heat-stressed plants treated with FPB produced more seeds than non-stressed plants. Imazethapyr reduced seed production. Heat-stressed junglerice treated with glufosinate produced fewer seeds than non-stressed plants. Conclusions: The joint effect of heat stress and sublethal dose of herbicides reduced junglerice sensitivity to the four rice herbicides tested after five generations. Heat stress and sublethal dose of the relatively recent auxinic herbicide florpyrauxifen-benzyl reduced junglerice sensitivity and increased seed production. Abstract Background , (junglerice) ingredients efficacy Objective Methods 45 (4 °C C florpyrauxifenbenzyl florpyrauxifen benzyl FPB, (FPB 0.125x, 0125x x 0.125x 0 125x 0.125x) (0.125x) 0.25x, 025x 0.25x 25x (0.25x) 0.25x. . treatment height panicles recorded plant1 plant- estimated Results Heatstressed stressed nonstressed non Conclusions (junglerice 4 ( (0.125x (0.25x

RESUMO: A produtividade do arroz no Sul do Brasil aumentou linearmente ao longo dos anos. A semeadura no início da janela é o principal contribuinte para o aumento da produtividade do arroz no sul do Brasil. No entanto, essa prática pode expor as plântulas de arroz ao estresse por baixa temperatura, aumentando os danos do herbicida e reduzindo a produtividade do arroz. Este trabalho teve como objetivo avaliar o efeito de épocas de semeadura na seletividade de herbicidas em caracteres agronômicos do arroz. Conduzimos experimentos de campo durante as safras 2010/11 e 2011/12 em Capão do Leão, RS, Brasil. O delineamento experimental foi em blocos casualizados completos com arranjo fatorial. O fator A foram a semeadura-precoce (em setembro) e a semeadura-tardia (em novembro); o fator B foram os tratamentos com herbicidas (bispyribac-sodium, cyhalofop-butyl, penoxsulam, metsulfuron-methyl e controle - sem herbicida). A resposta do arroz aos tratamentos com herbicidas diferiu entre os anos. Em 2010/11, o bispyribac-sodium, o penoxsulam e o metsulfuron-methyl prejudicaram o arroz apenas na semeadura-precoce. Em ambos os anos, a semeadura precoce do arroz promoveu maior potencial de rendimento, apesar dos danos dos herbicidas. As injúrias causadas pelos herbicidas bispyribac-sodium, penoxsulam e metsulfuron-methyl foram transitórias, não acarretando em perdas de produtividade. A temperatura fria próxima a aplicação aumenta a injúria dos herbicidas ALS.

ABSTRACT: Rice yield in Southern Brazil has increased linearly over the years. Early season sowing is the primary contributor to rice yield increase in Southern Brazil. However, that practice might expose rice seedlings to the risk of low-temperature stress, which can enhance herbicide injury and reduce rice yield. This research evaluated the effect of sowing dates on herbicide selectivity and agronomical rice traits. We conducted field experiments during the 2010/11 and 2011/12 growing seasons in Capão do Leão, RS, Brazil. The experimental design was a complete randomized block with a factorial arrangement. Factor A was early-sowed (in September) and late-sowed (in November); factor B was herbicide treatment (bispyribac-sodium, cyhalofop-butyl penoxsulam, metsulfuron-methyl, and nontreated check). Rice response to herbicide treatments differed between years. In 2010/11, bispyribac-sodium, penoxsulam, and metsulfuron-methyl injured rice only on early-sowed. In both years, early sowing rice promoted higher yield potential despite herbicide injury. The injury caused by the herbicides bispyribac-sodium, penoxsulam and metsulfurom-methyl was transient did not lead to yield losses. Cold temperature close the application increases the injury of ALS herbicides.

Abstract Background Eragrostis plana , introduced from South Africa, is the most important invasive perennial weed in the grasslands of Southern Brazil (“Pampa biome”), becoming a threat in neighboring countries. How temperature, light, and water potential affect seed germination is poorly understood but essential to understand its invasiveness and dissemination. Objective This study characterized the seed germination of E. plana from locations in the Brazilian Bioma Pampa under different conditions. Methods Seed germination was evaluated by using a time-to-event model across a wide range of temperatures (15 to 45C), light (total darkness or 12-h light), and water potentials (0, -0.08, -0.2, -0.25, -0.5, -0.75, -1, and -1.5 MPa). Results E. plana seeds did not germinate below 15C and at water potential lower than -0.75 MPa. Among populations, the highest germination was at 40C (> 90%). The base temperature for germination ranged from 12.3 to 15.6C across populations. E. plana did not germinate more than 40% at 25C, except for one population (Caçapava do Sul), with a germination capacity of 73%. Light is a requirement for a fraction of the seeds as darkness inhibits the germination of a fraction of the seeds as well. Conclusions E. plana could adapt to cooler temperatures, as shown by the ability of the Caçapava do Sul population to germinate at low temperatures. This ability for seed germination help to explain why E. plana has successfully invaded the rangelands of Southern Brazil, spreading around neighboring countries. Management strategies have to be urgently adopted to avoid its dissemination abroad. Africa biome, biome biome”) countries E conditions timetoevent time event 15 (1 45C, 45C C 45C) total 12h h 12 light) 0, 0 (0 0.08, 008 08 -0.08 0.2, 02 2 -0.2 0.25, 025 25 -0.25 0.5, 05 5 -0.5 0.75, 075 75 1, 1 -1 1.5 -1. MPa . MPa) 0.75 -0.7 populations > ( 90%. 90 90% 90%) 123 3 12. 156C 6C 40 25C Sul, Sul) 73 73% well abroad biome” 0.08 00 -0.0 0.2 -0. 0.25 0.5 07 7 - 1. 0.7 9 4 0.0 0. -0

Abstract Background Glyphosate is the most effective herbicide to control the invasive and perennial Eragrostis plana in Southern Brazil. However, one application has not been sufficient to prevent the regrowth of plants.Objective: The aim of this research was to evaluate the efficacy of glyphosate sprayed alone or mixed with fluazifop-p-butyl or flumioxazin on E. plana control and to investigate 14C-glyphosate absorption and translocation. Methods Plants with 2-3 tillers were treated with glyphosate (700 g a.e. ha-1), fluazifop-p-butyl (47 g a.i. ha-1), flumioxazin (100 g a.i. ha-1), glyphosate + fluazifop-p-butyl (700 g a.e. ha-1 + 47g a.i. ha-1), glyphosate + flumioxazin (700 g a.e. ha-1 +100 g a.i. ha-1). Weed control was evaluated visually for 28 d after treatment (DAT) when plants were harvested for shoot dry biomass determination. 14C-glyphosate absorption and translocation were measured at 24 and 72 h after treatment. Results Glyphosate at 700 g a.e. ha-1 controlled E. plana plants at 2-3 tillers. The mixture with fluazifop-p-butyl or flumizin did not significantly increase the level of control (87 and 86% at 7 DAT, respectively) but increased 14C-glyphosate translocation to the roots. Conclusions Glyphosate is effective on E. plana. However, applied with fluazifop-p-butyl could improve the control of this weed, especially when perennial plants of E. plana dominate the field, preventing their fast regrowth.

Abstract Background: Weedy rice (Oryza sativa L.) is the main weed of rice crop. The high genetic variability of weedy rice contributes to the high phenotypic diversity between biotypes and different responses to environmental stress. Objective: The present study aimed to evaluate the response of imidazolinone-susceptible and -resistant weedy rice populations to increased atmospheric [CO2]. Methods: The experiment was arranged in a complete randomized design with six replications. The treatments included two [CO2] concentration (700 and 400 μmol mol-1) and three treatments: resistant genotype (IMI-resistant) treated with imazethapyr; resistant genotype without imazethapyr, and a susceptible genotype without imazethapyr. Results: The IMI-resistant and -susceptible weedy rice responded similarly to [CO2] enrichment. Enhanced [CO2] increased competitive ability of the weedy rice populations tested, by means of increased plant height. Weedy rice seed production also increased with enhanced [CO2] by means of increased photosynthesis rate and reduced transpiration (increased water use efficiency). Increased seed production also means increased weed persistence as it increases the soil seedbank size. The application of imazethapyr on IMI-resistant weedy rice did not alter its response to [CO2]; conversely, increased [CO2] did not change the resistance level of weedy rice to imazethapyr. High [CO2] increased spikelet sterility, but this beneficial effect was negated by the overall increase in production of filled grains. Conclusions: Enhanced [CO2] concentrations increases weedy rice growth, photosynthesis rates, seed production and spikelet sterility; the imidazolinone application does not affect the response of weedy rice to enhanced [CO2] affects weedy rice response to imidazolinone herbicide.