Sourgrass (Digitaria insularis L.) and fleabane (Conyza spp. L.) constitute a major challenge to weed management in soybean [Glycine max (L.) Merr.] production systems in Brazil, especially when both are resistant to glyphosate and present concurrently. The aim of this study was to evaluate the interaction of haloxyfop-P-methyl [methyl(R)-2{4-{3-chloro-5(trifluoromethyl)-2-pyridyloxy] phenoxy} propanoate] and 2,4-D [2,4-Dichlorophenoxyacetic acid-N-methylmethanamine] to control sourgrass at three to four tillers and flowering stages and 12-to 15-cm fleabane at vegetative stage. The experiments were arranged in a randomized complete block design with four replicates and were conducted twice. Treatments were composed of haloxyfop-P-methyl and 2,4-D applied sequentially at 3-, 6-, and 12-d intervals.Treatments also included an untreated check, haloxyfop-P-methyl, and 2,4-D sequentially (without interval) and stand-alone applications of both herbicides. All treatments across experiments completely controlled fleabane plants, except haloxyfop-P-methyl alone. Haloxyfop-P-methyl applied ≥6 d before 2,4-D controlled flowering and three-to four-tiller sourgrass plants at rates of 50 and 100%, respectively. Based on results of this study, haloxyfop-P-methyl should be applied ≥6 d before 2,4-D in a sequential application structure to control fleabane and sourgrass (three or four tillers) when present concurrently.

O efeito residual duradouro de alguns herbicidas depende das características do solo e das moléculas, entretanto, a bioatividade do herbicida pode causar danos nas culturas em rotação/sucessão. A maneira mais comum de identificar a presença de herbicidas no solo, é pela implementação de bioensaios que utilizam uma espécie potencialmente sensível às moléculas herbicidas como indicador deste resíduo no solo. O objetivo foi identificar a sensibilidade da melancia como bioindicadora à resíduos de herbicidas pré-emergentes utilizados na cultura da soja. O ensaio foi conduzido em casa de vegetação, em vasos de 3 L, em delineamento por blocos ao acaso, com quatro repetições, em esquema fatorial de 3x4+1, onde o fator A foram os herbicidas diclosulam, [imazapyr + imazapic] e metribuzin, e o fator B as doses dos produtos comerciais [1/8D, 1/4D, 1/2D e D (dose recomendada em bula)] e mais o tratamento controle. Foram semeadas quatro sementes de melancia por vaso, contendo solo argiloso, após a aplicação dos herbicidas. As variáveis analisadas 30 dias após a emergência das plantas foram comprimento de parte aérea (cm), comprimento (cm), volume de raiz (mL), massa seca da parte aérea (g) e massa seca de raiz (g). Verificou-se que a melancia não germinou nos tratamentos com subdoses dos herbicidas diclosulam e metribuzin, e o crescimento reduziu nas subdoses do herbicida [imazapyr + imazapic]. Os resíduos de herbicidas estudados exerceram controle das plantas bioindicadora. Melancia possui sensibilidade aos herbicidas diclosulam, metribuzin e à mistura comercial dos herbicidas [imazapyr + imazapic], possuindo potencial para indicar resíduo destes herbicidas em solo argiloso.

The long residual period of pre-emergent herbicides can interfere with successor crops, causing a phenomenon named carryover. This study evaluated the residual effect of imazapyr + imazapic herbicides on cotton crop grown in succession to soybean. The experiment was conducted between September 2016 and March 2017, in a randomized block design with 4 replicates, where the treatments were four doses of imazapyr + imazapic, 75, 150, 225 and 300 g a.i. ha-1, and the control. The analyzed variables were chlorophyll a fluorescence, shoot height, root length and volume, dry shoot mass and root dry mass. The data were submitted to analysis of variance and Tukey’s test, at p ≤ 0.05. The reduction in photosynthetic performance indexes for treatments of 150, 225 and 300 g a.i. ha-1 at 15 days after emergence (DAE) and of 75 g a.i ha-1 at 60 DAE indicated a photoinhibitory effect of these herbicides on plants. However, shoot height, length, volume and root dry mass were not affected in the treatments tested. Therefore, the persistence of the herbicide in the soil was not enough to characterize a carryover effect in cotton 135 days after application (DAA).

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