Seletividade de herbicidas, aplicados em pós-emergência, às plantas de alfafa

Abstract

Foram conduzidos doi experimentos na UNESP/Jaboticabal, em casa-de-vegetação, com o objetivo de avaliar-se a toxicidade de diferentes herbicidas, aplicados em pós-emergênica, às plantas de alfafa. No primeiro, utilizou-se de um delineamento experimental com parcelas inteiramente casualizadas para avaliar-se os efeitos fitotóxicos dos seguintes herbicidas: MSMA, clethodim + óleo mineral, lactofen, fluazifop-pbutil, fomesafen + óleo mineral haloxyfop-methyl + óleo mineral, fenoxaprop-ethyl, chlorimuronethyl, halosulfuron + óleo mineral, nicosulfuron, acifluorfen, imazethapyr, bentazon + óleo mineral e cyanazine + simazine, todos em só dose. Foram feitas avaliações da fitotoxicidade por meio de notas, atribuídas visualmente, em função dos sintomas constatados nas plantas. A altura das plantas e o peso da matéria seca da parte área foram avaliadas no período de desenvolvimento inicial e após a primeira rebrota. No segundo experimento foi seguido mesmo esquema de instalação e condução do anterior, após escolherse os herbicidas e doses, sendo eles, o MSMA, chlorimuron-ethyl, imazethapyr, bentazon + óleo mineral, clethodim, clethodim + óleo mineral e bentazon + MSMA. Os herbicidas mais seletivos às plantas de alfafa foram haloxyfop-methyl, fluazifop-p-butil, fenoxaprop-ethyl, MSMA, imazethapyr, bentazon e clethodim isolado e adicionado de óleo mineral).

Herbicide selectivity in alfalfa crops

“…A similar result was found by Silva et al (2004). However, the phytotoxicity symptom found by Mello et al (2000) was considered as average, with decreased dry mass and lower plant development. Mesbah et al (2005) found injuries to alfalfa due to phytotoxicity caused by the herbicides imazethapyr and imazamox after application to plants 15 cm tall.…”

“…Silva et al (2004) showed that alfalfa treated with chlorimuron-ethyl showed initial symptoms of phytotoxicity with full recovery after 14 DAA. Mello et al (2000) obtained the same result, with less negative effects on alfalfa between the first and second cuts.…”

“…With respect to shoot biomass, no significant differences were observed for imazaquin, but differences were observed for nicosulfuron, whose larger doses caused a decrease in biomass. In the study by Mello (2000), nicosulfuron provided reductions in dry matter yield over 96%, which indicates high phytotoxicity to the crop.…”

“…Some crops, however, quickly metabolize the bentazon molecule into non-toxic forms, whereas susceptible plants do not possess this ability (Roman, 2007), as was found for alfalfa in this study. Mello et al (2000) also reported phytotoxicity and reduction in plant size and in dry matter yield. However, in an experiment conducted by Silva et al (2004), plants treated with bentazon showed initial symptoms of phytotoxicity with full recovery after 14 DAA and 90 DAA.…”

“…In their research, Mello et al (2000) concluded that haloxyfop-methyl, fluazifop-pbutyl and clethodim, all of which were ACCase inhibitors, were the most selective herbicides to alfalfa.…”