POSICIONAMENTO DO HERBICIDA OXADIAZON NA CULTURA DA CEBOLA EM SEMEADURA DIRETA

Abstract

The onion crop production system has undergone major transformations, among them the introduction of hybrid cultivars and the implementation of direct seeding, but there is a difficulty in the weeds management for the current model of cultivation with the herbicides available in the marketplace. The present work aims to evaluate options for positioning the oxadiazon herbicide, which acts as a protox inhibitor in the onion crop, implanted through direct sowing with the fractionation and scaling of the current label recommendation. For this purpose, an experiment was carried out in the city of Uberlândia, state of Minas Gerais, using the hybrid onion Akamaru®, implanted through direct sowing in beds with 9 treatments and 4 replications, with a randomized block design in linear 5-meter plots. The treatments with oxadiazon application were 1 day after sowing (DAS) in active ingredient doses of 1000 g ha-1, 500 g ha-1, 250 g ha-1, 125 g ha-1, also with application of 125 g ha-1 1 DAS followed by 4 foliar applications of 125 g ha-1 in a spray interval of 21 days and 125 g ha-1 1 DAS followed by an application of 125 g ha-1 and another 3 applications of 250 g ha-1 in an interval of 21 days, compared with an application of 1,400 g ha-1 of pendimentalin 1 DAS, control treatments were one weed free and another one with the presence weeds in the area. Evaluations were carried out to quantify the effects of phytotoxicity on the crop through visual assessments, effects on plant size, chlorophyll determination, electrolyte release rate, bulb diameter and productivity. The weeds control present in the experiment was being evaluated by counting in sample squares of 0.25 m², percentages of effectiveness through the coverage of each weed species in the plot and with the collection for dry matter determination. Pre-emergence oxadiazon applications above 500 g ha-1 and the pendimentalin standart caused visual injuries in the crop, such as wilting and plant death, which consequently reduced productivity and bulb size, although they did not differ in chlorophyll determination, growth rate and electrolytes release. Treatments with application of 125 and 250 g ha-1 of oxadiazon before and after crop emergence did not affect any of the evaluated parameters. In the control of infesting weeds, all treatments presented initial control when applied in pre-emergence. In the residual control, the best treatments were oxadiazon applications of 500 and 1,000 g ha-1 in pre-emergence and the treatments with sequential applications in the 21-day interval of 125 and 250 g ha-1. Based on the results of phytotoxicity, productivity and efficacy in weed control, it was concluded that oxadiazon is safe and effective for the direct seeding system of the onion crop when applied at a dose of 125 g ha-1 1 DAS followed by one application of 125 g ha-1 and 3 more applications of 125 - 250 g ha-1 in a spray interval of 21 days.