Abstract
Fleabane (Conyza spp.) has spread in no-tillage areas of Paraná State (PR), Brazil, and currently represents one of the main challenges related to weed control, particularly during off-season period. For this purpose, two experiments were carried out in Campina da Lagoa (PR) and Floresta (PR) with the aim of assessing the efficacy of herbicide treatments applied to fleabane areas during the off-season period between maize harvest (June to July) and soybean sowing (November). Treatments consisted of herbicide treatments (glyphosate + 2, 4-D; glufosinate, MSMA) targeting the control of fleabane plants in POST, tank-mixed with residual herbicides (metsulfuron, chlorimuron, diclosulam, imazethapyr, imazaquin, flumioxazin, metribuzin, amicarbazone and isoxaflutole) to control the emergence and growth of new flushes in PRE. Applications were performed when fleabane plants reached a height of 2 cm. Evaluation on both efficacy and residual weed control was accomplished from the first day of application day to 75 days after application (soybean crop sowing). Glyphosate + 2, 4-D mixture was efficient for burndown of Conyza spp. in all situations. During 75 day off season period, diclosulam and chlorimuron were the best options for controlling fleabane emergence when mixed with any other options of herbicide treatments, for the control in POST. Mixtures of glyphosate + 2, 4-D with metribuzin and glufosinate with flumioxazin, metribuzin and isoxaflutole maintained good fleabane control throughout the whole 75 days off season period. Fall management was an effective option for fleabane control. Key words: Conyza spp., herbicide resistance, management, residual effect, weeds.
Highlights
Fleabane (Conyza spp.) ranks among the top ten main weeds distributed around the world
In Brazil, glyphosate-resistant Conyza bonariensis and C. canadensis were first reported in 2006 both in citrus orchards located in São Paulo State (Moreira et al, 2007) and in grain-producing areas in Rio Grande do Sul (Vargas et al, 2007)
In Campina da Lagoa (PR) treatments with glyphosate + 2, 4-D and glufosinate provided >90% control for fleabane, while MSMA presented the lowest efficacy (81%) among burndown options. For this particular option, tank mixing these herbicides with residual herbicides increased control to >87%
Summary
Fleabane (Conyza spp.) ranks among the top ten main weeds distributed around the world. Different species in this genus stand out in this ranking due to their ability to develop resistance to herbicides of different mechanisms. In the United States, the controlling failures were observed after only three years of continued use of glyphosate in post-emergence (POST). In 2001, the first case of Conyza canadensis resistant to glyphosate was reported Vangessel (2001). In Brazil, glyphosate-resistant Conyza bonariensis and C. canadensis were first reported in 2006 both in citrus orchards located in São Paulo State (Moreira et al, 2007) and in grain-producing areas in Rio Grande do Sul (Vargas et al, 2007). Resistant biotypes of Conyza sumatrensis were reported in Paraná State (Santos et al, 2014)
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