Identificação de resistência aos herbicidas utilizados no algodoeiro em biótipos de Amaranthus retroflexus e Amaranthus viridis oriundos da regiões produtoras da Bahia, Goiás, Mato Grosso e Mato Grosso do Sul

Abstract

The shortage of registered products in cotton growing for several years for the same mechanisms of action has promoted pression selection on weed species, selecting resistant biotypes. Thus, there are been complaints from producers caused by the deficit of control provided by certain herbicides, increasing the amount of plants not controled in crops. Thus, the objective was to investigate the optimum dose control of trifloxysulfuron-sodium and pyrithiobac-sodium applied in pre-emergence control of four Amaranthus species, to investigate the possible occurrence of resistant biotypes of Amaranthus hybridus collected from cotton producing states (MS, GO, BA and MT) with herbicides ALS inhibitors applied in post-emergence, and investigate cases of resistance in biotypes of Amaranthus hybridus to the herbicides: Photosystem II inhibitors, ALS inhibitors, tubulin inhibitors, cell division inhibitors all applied in pre-emergence. All experiments were performed in greenhouse. It is thus that the herbicides trifloxysulfuron-sodium and pyrithiobac-sodium applied in pre-emergence control were effective in all tested species of pigweed, and the most sensitive to the applications was Amaranthus lividus and Amaranthus hybridus to lethal and sublethal doses and can be recomend of control of such plants in pre-emergence applications. In the evaluation of suspected resistant biotypes of Amaranthus retroflexus in post emergence applications of trifloxysulfuron-sodium can be confirmed resistance in samples of MS 1, MS 2, GO 3, GO 4 and GO 6, and applications of pyrithiobac-sodium confirmed cases of resistance in samples of MS 2, GO 3, GO 4 e GO 6. Biotypes of A. viridis confirmed resistance only in MS 1 .In applications carried out in pre-emergence of Amaranthus retroflexus biotypes, to verify the suspected herbicide resistance to ALS inhibitors, tubulin inhibitors, proteins and nucleic acids inhibitors and Photosystem II inhibitors, was possible to identified resistant biotypes present in samples from states of Mato grosso do sul (MS), Goiás (GO), Bahia (BA) and Mato Grosso (MT). A. retroflexus were identified resistant to atrazine (GO 3 and MT 13), prometryne (GO 3, GO 5, GO 6 and MT 13), rifloxysulfuron-sodium (MS 2, GO 3, GO 4, GO 5, GO 6 and MT 13) and to pyrithiobac-sodium herbicide (MS 2, GO 3, GO 4, GO 5 e GO 6). Was found resistance in biotypes of A. viridis to atrazine (BA 7 and BA 9), to prometryn (BA 7, BA 8, BA 9, BA 10 and BA 11), to trifloxysukfuron-sodium (BA 7, BA 8, BA 9 and BA 11).Was been identified yet, cross-resistance between A. retroflexus biotypes to ALS-inhibiting herbicides (trifloxysulfuron-sodium X pyrithiobac-sodium). Cross-resistance was found in biotypes of both species of Amaranthus between the triazine herbicides (atrazine X prometryn). Also in the same samples of A. retroflexus and A. viridis confirmed cases of multiple resistance among ALS inhibitors and inhibitors of the FSI. There was no confirmation of resistance to all biotypes tested to herbicides like trifluralin, s-metolachor and diuron, can be used as an alternative in the pre-emergence management control for resistant weeds biotypes.