Sumatran fleabane (Conyza sumatrensis [Retz.] E. Walker) control in soybean with combinations of burndown and preemergence herbicides applied in the off-season

Sumatran fleabane (Conyza sumatrensis [Retz.] E. Walker) can be found in many different agricultural environments and impact different crops, such as soybeans and corn. It is believed that the application of burndown and preemergence herbicides in the off-season are effective in controlling Sumatran fleabane in soybean crops. The objective was to evaluate the effectiveness of burndown and preemergence herbicides in the off-season, with one or two applications, in the control of Sumatran fleabane in soybean cultivation. Five field experiments were conducted in Maripá, state of Paraná (PR), Brazil. The treatments consisted of the application of burndown herbicides in combinations with preemergence ones, with one or two applications. Control of Sumatran fleabane and soybean yield were evaluated. With the set of experiments, it is highlighted that the strategy combining more applications, with different herbicides, burndown and preemergence, is more promising in the control of Sumatran fleabane. When comparing synthetic auxins, dicamba and triclopyr stand out. For sequential application, worse performance was observed for diquat. Combinations between burndown and preemergence herbicides were effective in controlling Sumatran fleabane, for pre sowing application in soybean. With emphasis on managements with sequential applications of saflufenacil with glufosinate or glyphosate. The strategy combining more applications, with different herbicides, burndown and preemergence herbicides, is more promising in the control of Sumatran fleabane.

Control of Conyza spp. with sequential application of glufosinate in soybean pre-sowing / Controle de Conyza spp. com aplicação sequencial de glufosinate em pré-semeadura da soja

Conyza spp. is among the main weeds reported worldwide. Due to its aggressiveness, such as high seed production and dispersion, and the growing reports of biotypes resistant to glyphosate, paraquat, and other herbicides, different control practices are required. Thus, this study aimed to evaluate the efficacy of herbicides with sequential application of glufosinate in soybean pre-sowing for control of Conyza spp. with indicative of resistant to paraquat. The study was carried out in the field, at Assis Chateaubriand and Palotina, state of Paraná, Brazil, in the 2018/19 season. The experiments were conducted in a randomized block design with four replications. The treatments consisted in application of glyphosate, 2,4-D, saflufenacil, glufosinate, saflufenacil/imazethapyr, diclosulam, paraquat/diuron, paraquat and imazethapyr/flumioxazin, at different combinations, in soybean pre-sowing. Control of Conyza spp., crop injury to soybean plants and variables related to agronomic performance (plant height and yield) were evaluated. All treatments were selective for soybean, which showed stronger crop injury in the presence of diclosulam herbicide, but this did not compromise soybean agronomic performance. In general, control levels were high for the treatments used. Except for paraquat treatments, in the area with the highest frequency of Conyza spp. with indicative of resistant to paraquat, and imazethapyr/flumioxazin treatment in both areas. These control results emphasized the importance of glufosinate in this management system and showed promising results for saflufenacil/imazethapyr.(AU)

A planta daninha Conyza spp. está entre as principais encontradas em todo o mundo. Devido a sua agressividade, como elevada produção e dispersão de sementes e os crescentes relatos de biótipos resistentes ao glyphosate, paraquat e outros herbicidas, faz-se necessário o uso de diferentes ferramentas de manejo. Assim, o objetivo deste estudo foi avaliar a eficácia de herbicidas com aplicação sequencial de glufosinate em pré-semeadura da soja, no controle de Conyza spp. com indicativo de resistência ao paraquat. O estudo foi realizado em campo nos municípios de Assis Chateaubriand e Palotina, estado do Paraná (PR), Brasil, na safra 2018/19. O delineamento experimental utilizado foi o de blocos casualizados, com quatro repetições. Os tratamentos foram compostos pela aplicação de glyphosate, 2,4-D, saflufenacil, glufosinate, saflufenacil/imazethapyr, diclosulam, paraquat/diuron, paraquat e imazethapyr/flumioxazin, em diferentes combinações em pré-semeadura da soja. Foram avaliados controle de Conyza spp., sintomas de injúria nas plantas de soja e variáveis relacionadas ao desempenho agronômico (altura de plantas e produtividade). Todos os tratamentos mostraram-se seletivos a soja. Visualizou-se maiores sintomas de injúria quando se tinha a presença do herbicida diclosulam, mas não resultou em danos ao desempenho agronômico da soja. De forma geral os níveis de controle foram altos para os tratamentos utilizados, em exceção para os tratamentos com paraquat na área que apresentava maior frequência de Conyza spp. com indicativo de resistência a este herbicida, e para o tratamento com imazethapyr/flumioxazin nas duas áreas. Estes resultados de controle enfatizam a importância do glufosinate neste sistema de manejo e demostram resultados promissores para saflufenacil/imazethapyr.(AU)

Effects of nozzle types and 2,4-D formulations on spray deposition.

The objective of this study was to evaluate the effects of nozzle types and 2,4-D formulations on spray deposition on different targets. Two field experiments were carried out in a completely randomized design, and treatments were arranged in a factorial scheme. Species in experiment 1 were Sumatran fleabane (Conyza sumatrensis) and Brazil pusley (Richardia brasiliensis) and in experiment 2 were soybeans (Glycine max) and Benghal dayflower (Commelina benghalensis). For both experiments, the first factor corresponded to spray nozzles with different settings (AD 110.015 - 61 and 105 L ha-1; AD 015-D - 75 and 146 L ha-1; XR 110.0202 - 200 L ha-1; and ADIA-D 110.02 - 208 L ha-1) and the second factor consisted of two formulations of 2,4-D (amine and choline). The formulation of 2,4-D choline has contained Colex-D™ Technology. Similar or higher spray deposition was observed on the leaves and artificial targets when using 2,4-D choline as compared to the 2,4-D amine formulation, and these differences in deposition were more evident for nozzles applying lower spray volumes. Deposition was more affected by nozzle type when amine formulation was used, compared to choline formulation.

Physiological, morphological and biochemical studies of glyphosate tolerance in Mexican Cologania (Cologania broussonetii (Balb.) DC.).

In recent years, glyphosate-tolerant legumes have been used as cover crops for weed management in tropical areas of Mexico. Mexican cologania (Cologania broussonetii (Balb.) DC.) is an innate glyphosate-tolerant legume with a potential as a cover crop in temperate areas of the country. In this work, glyphosate tolerance was characterized in two Mexican cologania (a treated (T) and an untreated (UT)) populations as being representatives of the species, compared in turn to a glyphosate-susceptible hairy fleabane (S) (Conyza bonariensis (L.) Cronq.) population. Experiments revealed that T and UT Mexican cologania populations had a higher tolerance index (TI), and a lower shikimic acid accumulation and foliar retention than the hairy fleabane S population. Absorption and translocation, leaf morphology and metabolism studies were only carried out in the Mexican cologania T population and the hairy fleabane S population. The latter absorbed 37% more (14)C-glyphosate compared to the Mexican cologania T at 96 h after treatment (HAT). Mexican cologania T translocated less herbicide from the treated leaf to the remainder of the plant than hairy fleabane S. The Mexican cologania T presented a greater epicuticular wax coverage percentage than the hairy fleabane S. This morphological characteristic contributed to the low glyphosate absorption observed in the Mexican cologania. In addition, the Mexican cologania T metabolized glyphosate mainly into AMPA, formaldehyde and sarcosine. These results indicate that the high glyphosate tolerance observed in Mexican cologania is mainly due to the poor penetration and translocation of glyphosate into the active site, and the high glyphosate degradation into non-toxic substances.