Tolerância da cebola implantada por semeadura direta ao flumioxazin aplicado em pós-emergência inicial

Weed management in onion culture is a fundamental practice to reduce or eliminate interference from weeds community, since the crop, especially in direct sowing system, presents slow initial growth and low competitive capacity. In this sense, for the correct use of the herbicides it is necessary to know the effects provided by the doses in the onion crop as well as to quantify this effect for the different phenological stages. In view of the above, the purpose of this study was to evaluate the tolerance of the onion in a system of direct sowing to flumioxazin applied in the initial post-emergence in different phonological stages. The experiment was carried out in a completely randomized design, with four replications in factorial arrangement 4 × 5 + 1, the first factor being the flumioxazin (2.5, 5.0, 7.5 and 10 g ha-1) doses (whip, 1st leaf, 2nd leaf, 3rd leaf and 4th leaf), as well as additional treatment (control without application). Leaf height, shoot dry matter, diameter and weight of bulb’s were evaluated. Application of flumioxazin in post-emergence of onion reduced all the variables assessed when held up until the stage of two true leaves. Negative effects were greater with increase of the dose of the herbicide in the initial stages of growth of the onio. On the other hand, flumioxazin applied from the third dose-independent true leaf did not affect any of the analyzed parameters. After the emission of the third leaf the onion presented tolerance to flumioxazin.