Eficácia do diquat no controle de Hydrilla verticillata, Egeria densa e Egeria najas e toxicidade aguda para o Guaru (Phallocerus caudimaculatus), em condições de laboratório

Abstract

RESUMO -No Brasil, as macrófitas aquáticas submersas, Egeria densa e Egeria najas, têm causado prejuízos aos usos múltiplos da água. Hydrilla verticillata foi recentemente introduzida, mas tem histórico como planta problemática nos EUA, no México e na Austrália. O objetivo deste trabalho foi avaliar as suscetibilidades relativas dessas três macrófitas aquáticas ao diquat e os riscos da utilização desse herbicida para o guaru (Phallocerus caudimaculatus). Para isso, foram instalados ensaios em condições de laboratório, a fim de avaliar a suscetibilidade relativa das três macrófitas por meio da manutenção de ponteiros dessas plantas em soluções contendo 0,0; 0,2; 0,4; 0,8; e 1,6 mg L -1 de diquat (Reward ® ) por 14 dias. A avaliação foi realizada pela variação do acúmulo de matéria fresca e do comprimento dos ponteiros no período de exposição ao herbicida. H. verticillata mostrou maior sensibilidade ao diquat em comparação com as duas macrófitas do gênero Egeria, mesmo em baixas concentrações do herbicida. Nas maiores concentrações, E. densa mostrou maior sensibilidade que E. najas. O risco da aplicação do diquat para P. caudimaculatus foi estimado pela toxicidade aguda. Alevinos de P. caudimaculatus de 0,4 ± 0,2 mg foram expostos a soluções de 0,0; 1,0; 5,0; 10,0; 15,0; 20,0; 25,0; e 30,0 mg L -1 de diquat. A concentração letal de 50% (CL(I) (50;96h)) do diquat estimada para P. caudimaculatus foi de 7,17 mg L -1. Para P. caudimaculatus, a toxicidade aguda foi superior à concentração recomendada para o controle de macrófitas aquáticas submersas, indicando risco muito baixo para esse peixe.Palavras-chave: macrófitas aquáticas, toxicidade, herbicida, risco ambiental.ABSTRACT -In Brazil, the submerged plants Egeria densa and Egeria najas have caused damage to multiple uses of water. Hydrilla verticillata has been recently introduced, but it has a history as a problem plant in the U.S., Mexico and Australia. The objectives of this work were to assess the relative susceptibilities of these three macrophytes to diquat and the risks of using this herbicide for fish guppy (Phallocerus caudimaculatus). Thus, laboratory assays were set up to assess the relative susceptibility of the three macrophytes. Pointers of these plants were kept in solutions containing 0.0, 0.2, 0.4, 0.8 and 1.6 mg L -1 diquat (Reward ® ) for 14 days. The evaluation was performed based on the variation of fresh matter weight and length of the pointers during the period of exposure to the herbicide. H. verticillata was more sensitive to diquat, compared with the two Egeria macrophytes, even at low herbicide concentrations. At higher herbicide concentrations, E. densa was more sensitive than E. najas. The risk of applying diquat to P. caudimaculatus was estimated by acute toxicity. Fingerlings of P. caudimaculatus of 0.4 ± 0.2 g were exposed to solutions of 0.0, 1.0, 5.0, 10.0, 15.0, 20.0, 25.0 and 30.0 mg L -1 of diquat. The 50% lethal concentration (LC (I) (50.96h)) of diquat estimated for P. caudimaculatus was 7.17 mg L -1 . For P. caudimaculatus, a...

EFFECTIVENESS OF DIQUAT, BOTH ISOLATED AND ASSOCIATED WITH COPPER SOURCES IN CONTROLLING THE Hydrilla verticillata SUBMERGED MACROPHYTES AND ANKISTRODESMUS Gracilis microphyte

“…Comparing these studies, it was verified that this plant has greater sensibility to diquat, both isolated and associated with copper sources, since, according to Henares et al (2011), 14 days after diquat application (1.6 mg L -1 ) there still was E. densa and E. najas fresh biomass. According to Langeland et al (2002) and Glomski et al (2005), there was H. verticillata dry biomass on day 21 with the application of 0.25 mg L -1 and 0.37 mg L -1 , respectively.…”

“…According to Henares et al (2011), Hydrilla verticillata is more sensitive to diquat than other (Table 2). The high chlorophyll a reduction on day 15 DAA for A. gracilis algae is similar to what was described for diquat; copper oxychloride and hydroxide reduced photosynthetic activity, with values between 0.09 and 0.14 μg L -1 (Garlich et al, 2016a).…”

“…Studies on its effectiveness were performed with Hydrilla verticilata, Egeria densa and Egeria najas (Henares et al, 2011) and Ceratophyllum demersum (Garlich et al, 2016b).…”

“…and Scenedesmus obliquus (Ma and Liang, 2001), Pseudokirchneriella subcapitata (Schamphelaere et al, 2005), Chlorella pyrenoidosa (Xia and Tian, 2009) and Ankistrodesmus gracilis (Garlich et al, 2016a). Diquat and copper sources mixtures are described as effective to control macrophytes or algae (Martins et al, 2008;Henares et al, 2011;Garlich et al, 2016a,b).…”

Improving diquat efficacy on grasses by adding adjuvants to the spray solution before use

“…It is also used as an aquatic herbicide (Ahrens, 1994;Henares et al, 2011) and as a desiccant in potato, alfalfa, and other crops to aid harvesting (Calderbank & Slade, 1976). Its application rates are 400-1000 g a.i./ha (Tomlin, 2000).…”