Abstract Urochloa panidoides P. Beauv is a problematic weed in the Argentine Northwest and glyphosate resistant biotypes have been detected. The aims of this study were to characterize the dynamics of emergency in relation to environmental conditions and to evaluate alternatives of chemical control on populations resistant to glyphosate. For two consecutive growing seasons 2015-2016 and 2016-2017, in crop areas, two studies were conducted. In the first study, every 15 days destructive seedling counts were carried out in six plots of 1m2. Temperature and rainfall were recorded. With the temperature, the calculation of the accumulated degree days (GDDA) was carried out. In the second study, in a randomized block experimental design, the efficacy of six pre-emergent residual herbicide treatments was visually evaluated at 30, 45 and 60 days after application (DDA). In both campaigns, the emergence dynamics of seeds that broke dormancy adjusted to the temperature, however, rainfall played a crucial role in triggering the germination process. This is evidenced by observing that in Tucumán U. panicoides emerges from the spring rains. Regarding pre-emergent residual herbicide treatments, Imazethapyr, sulfometuron + chlorimuron and clomazone had a control efficiency greater than 80% up to 60 DAA. S-metolachlor and diclosulam showed acceptable controls (above 88%) up to 30 DAA and after 45 DAA, and after 45 ADD, their controls were unsatisfactory. It is concluded that the herbicides Imazetapir, sulfometuron + chlorimuron (inhibitors of the enzyme acetolactate synthetase) and clomazone (inhibitor of dioxy-D-xylulose phosphate synthase) are useful residual chemical alternatives for the management of U. panicoides in previous fallows for soybean and corn crops.

Resumen Urochloa panidoides P. Beauv es una maleza problemática en el noroeste argentino y se han detectado biotipos resistentes a glifosato. Los objetivos de este estudio fueron caracterizar la dinámica de emergencia en relación a las condiciones ambientales y evaluar alternativas de control químico residual sobre biotipos resistentes a glifosato. Durante dos campañas consecutivas, 2015-2016 y 2016-2017, en campos en producción, se realizaron dos estudios. En el primer estudio, cada 15 días se realizaron conteos destructivos de plántulas en seis parcelas de 1m2. Se registró temperatura del aire y precipitaciones. Con la temperatura, se realizó el cálculo de los grados días acumulados (GDDA). En el segundo estudio, en un diseño experimental en bloques completos al azar se evaluó visualmente la eficacia de seis tratamientos herbicidas residuales pre-emergentes a los 30, 45 y 60 días después de la aplicación (DDA). En ambas campañas la dinámica de emergencia de semillas que rompieron dormición ajustó a la temperatura. Sin embargo, las precipitaciones jugaron un rol crucial para desencadenar el proceso de germinación. Lo anterior se evidencia observando que en Tucumán U. panicoides emerge a partir de las lluvias de primavera. Lluvias esporádicas anteriores a esta estación generan nulos a muy bajos porcentajes de emergencias porque el mayor porcentaje de semillas se encuentra en estado de dormición. En cuanto a los tratamientos con herbicidas residuales pre-emergentes, imazetapir, sulfometuron + clorimuron y clomazone registraron un control superior al 80 % hasta los 60 DDA. S-metolacloro y diclosulam presentaron controles aceptables (por arriba del 88 %) hasta los 30 DDA y a partir de los 45 DDA sus controles fueron no satisfactorios. Se concluye que los herbicidas Imazetapir, sulfometuron + clorimuron (inhibidores de la enzima acetolactato sintetasa) y clomazone (inhibidor de la dioxi-D-xilulosa fosfato sintasa) son alternativas químicas residuales útiles para el manejo de U. panicoides en barbechos previos para los cultivos de soja y maíz.

In Argentina, Tucumán province is the main producer of sugarcane. Among the factors that affect this cultivation, weeds are the main limiting factor. For this reason, weed communities present in sugarcane lots with the commercial cultivar LCP 85-384 were characterized and compared phytosociologically at the stages of ratoon four and eight. For each ratoon, 240 rings of 1 square meter were thrown. Species were identified from each ring; individuals were counted, and dry weight was determined. Subsequently, the phytosociological parameters frequency, dominance, density, importance value index, diversity indices and similarity index were calculated. In ratoon four, 12 species were identified, while in ratoon eight there were 26 species. In both ages, Dicotyledonous outnumbered Monocotyledonous. Regarding the cycle, in ratoon four there were 5 annual species and 7 perennial species, while in ratoon eight there were 18 annual species and 8 perennial species. According to the importance value index, Cynodon dactylon, Cyperus rotundus, and Sorghum halepense were relevant in both cutting ages, while other species such as Sicyos polyacanthus were relevant only in ratoon eight. Regarding diversity, ratoon four presented a Shannon Wiener index of 2.07 and a Simpson index of 0.87, while ratoon eight registered higher values (2.77 and 0.94, respectively), proving greater diversity of species in ratoon eight. The Jaccard similarity index was 26%, close to the threshold.

En Argentina, la provincia de Tucumán es la principal productora de caña de azúcar. Entre los factores que afectan al cultivo, las malezas constituyen la principal limitante en la producción. Por ello se caracterizaron y compararon fitosociológicamente comunidades de malezas presentes en lotes de caña de azúcar con el cultivar comercial LCP 85-384, en edades soca cuatro y ocho. Para cada edad, se lanzaron 240 aros de 1 metro cuadrado. De cada aro se identificaron las especies, se contaron los individuos y se determinó el peso seco. Posteriormente se calcularon los parámetros fitosociológicos frecuencia, dominancia, densidad, índice de valor de importancia, índices de diversidad e índice de similitud. En soca cuatro se identificaron 12 especies, mientras que, en soca ocho fueron 26 especies. En ambas edades las dicotiledóneas superaron en número a las monocotiledóneas. En cuanto al ciclo, en soca cuatro se registraron 5 especies anuales y 7 especies perennes, mientras que, en soca ocho fueron 18 especies anuales y 8 especies perennes. Según el índice de valor de importancia, Cynodon dactylon, Cyperus rotundus, y Sorghum halepense fueron relevantes en ambas edades de corte, mientras que otras especies como Sicyos polyacanthus fueron relevantes solo en soca ocho. En cuanto a la diversidad, soca cuatro, presentó un índice de Shannon Wienner de 2,07 y un índice de Simpson de 0,87, mientras que, soca ocho registró valores superiores (2,77 y 0,94, respectivamente), comprobándose mayor diversidad de especies en caña soca de 8 años. El índice de similitud de Jaccard fue 26 %, cercano al umbral.

RESUMO: As plantas daninhas constituem o principal fator limitante na produção de agroecossistemas de cana-de-açúcar argentinos. O objetivo deste trabalho foi analisar a composição florística e fitossociológica de plantas daninhas na cultura da cana-de-açúcar em diferentes regiões agroecológicas. Entre 60 e 90 dias a partir do surgimento da cultura, para cada região foram amostrados 15 lotes. Em cada um deles foi lançado um quadrado de 0,5 m2, seis vezes ao acaso. As espécies encontradas foram identificadas. Posteriormente, o peso da biomassa fresca e seca foi determinado por aro e por espécie. Frequência, densidade, dominância, índice de valor de importância, índice de diversidade das espécies de Shannon-Wiener e Simpson e índice de similaridade de Jaccard foram calculados. Para a interpretação da similaridade, foi utilizado o método de agrupamento da média do grupo (UPGMA). Em geral, 35 espécies foram identificadas, sendo 24 dicotiledôneas e 11 monocotiledôneas, das quais 18 eram anuais e 17 perenes. De acordo com o índice de importância, as famílias mais importantes foram Poaceae, Cyperaceae, Euphorbiaceae, Amaranthaceae e Asteraceae. Os resultados analisados em cada região coincidem em destacar a importância das espécies Panicum maximum, Sorghum halepense, Cyperus rotundus, Cynodon dactylon e Euphorbia hyssopifolia. As regiões de maior e menor diversidade foram a planície deprimida sub-região planície deprimida não salina e a planície Chaco-Pampeana subúmida-úmida, respectivamente. A semelhança foi de 53% entre a planície deprimida sub-região planície deprimida salina e a planície deprimida sub-região planície deprimida não salina e de 47% entre Pedemonte úmida e perúmida e a Planície Chaco-pampeana subúmida-úmida. O cluster hierárquico e o índice de Jaccard mostraram resultados semelhantes.

ABSTRACT: Weeds constitute the main constraint on the productivity of sugarcane agroecosystems in Argentina. This work aimed to analyze the floristic and phytosociological composition of sugarcane weed communities in different agroecological areas in Tucumán. Fifteen plots from each area were sampled 60 to 90 days after crop shooting, by throwing a 0.5 m x 0.5 m quadrat metallic frame six times in random directions in each of the plots. Species found within the frame were identified. Later, fresh and dry biomass weight were calculated per quadrat sample and species. Frequency, density, dominance, importance value index, Shannon-Wiener and Simpson species diversity index and Jaccard similarity index were calculated. The unweighted pair group method with arithmetic mean (UPGMA) was used to interpret similarity. Overall, 35 species were identified, 24 of which were dicotyledons and 11 monocotyledons. Eighteen of them were annual species, versus 17 which were perennial. Considering IVI, the most outstanding families were Poaceae, Cyperaceae, Euphorbiaceae, Amaranthaceae and Asteraceae. The results obtained in all the areas revealed the importance of the species Panicum maximum, Sorghum halepense, Cyperus rotundus, Cynodon dactylon and Euphorbia hyssopifolia. The areas with greater and less diversity were the Depressed Plain-Non-Saline Depressed Plain Subregion and the Subhumid-Humid Chaco-Pampean Plain, respectively. There was a 53% similarity between the Depressed Plain-Saline Depressed Plain and the Depressed Plain-Non-Saline Depressed Plain, and a 47% similarity between the Humid and Perhumid Foothills and the Subhumid-Humid Chaco-Pampean Plain. Hierarchical clustering and Jaccard index led to similar results.

ABSTRACT This work aimed to study the germination of Megathyrsus maximus seeds when exposed to high temperatures, as well as to evaluate the effects of different seed planting depths and sugarcane crop residue amounts on weed emergence. In the laboratory, germination and biomass of seeds with and without glumes were determined when exposed to 0, 40, 60, 80 and 100 oC, for five minutes. Two experiments were performed in the greenhouse to assess the emergence rate in relation to different weed seed planting depths (0, 0.5, 1, 2, 3, 4, 5, 7 and 8 cm) on the one hand, and in relation to different sugarcane crop residue quantities (0.5, 8, 11, 13, 15 and 18 t ha-1) on the other. Temperature tests were analyzed by means of covariance analysis, whereas greenhouse tests were analyzed with regression. The highest germination percentages for seeds with and without glumes were 48 and 35%, respectively, and they were obtained at 40 oC. The lowest values were 28 and 7% for seeds with and without glumes, respectively, and they were obtained at 80 oC. Seed planting depth had a negative effect on weed emergence: the control led to 51% emergence, which dropped to 23.3% at 7 cm and eventually to zero at 8.0 cm. Crop residues had a negative effect on emergence as well: when residue quantities ranged from 0 to 18 t ha-1, emergence decreased from 64.8 to 0%.Thus we can conclude that sugarcane management strategies affect M. maximus germination and emergence.

RESUMEN Se estudió la germinación de semillas de Megathyrsus maximus al exponerlas a altas temperaturas y el efecto de diferentes profundidades de siembra y cantidades de residuos de cosecha en la emergencia de las plántulas. En laboratorio, se determinó la germinación y biomasa de semillas con y sin glumas y glumelas, expuestas a 0, 40, 60, 80 y 100 oC durante cinco minutos. Se realizaron dos experimentos en invernáculo para evaluar la emergencia de la maleza, primero a diferentes profundidades de siembra: 0, 0.5, 1, 2, 3, 4, 5, 7 y 8 cm. Posteriormente, se evaluó emergencia con diferentes cantidades de residuos de cosecha: 0, 5, 8, 11, 13, 15 y 18 t ha-1. Los resultados de los ensayos de temperatura se analizaron mediante análisis de covarianza y los datos de los ensayos de invernáculo mediante regresión. Los máximos porcentajes de germinación para semillas con y sin glumas y glumelas se obtuvieron a 40 oC y fueron del 35 y 48%, respectivamente; los mínimos valores se registraron a los 80 oC y fueron del 7 y 28%, respectivamente. La profundidad de siembra afectó la emergencia: un 51% se registró en el testigo, valor que disminuyó al 23,3% a los 7 cm y a 0% a los 8 cm. Los residuos de cosecha también afectaron la emergencia: con 0 a 18 t ha-1, esta disminuyó del 64,8 al 0%. Puede concluirse que las estrategias implementadas en el manejo del cultivo de caña de azúcar afectarán la germinación y emergencia de M. maximus