Elephantopus mollis Kunth (Asteraceae): fluxo de emergência e curva de dose-resposta a herbicidas

Abstract

Elephantopus mollis is a Asteraceae family species recently found in soybean crops / winter pastures in the central-western region of Rio Grande do Sul, Brazil. Its presence has reduced yields and increased the cost of production of these crops. In order to get the emergency pattern of the species throughout the year and its sensitivity to the main herbicide used in these crops it is that took place this work. To determine the emergency flow and the seed bank in the area two experiments were conducted in a rural area of the municipality of Tupanciretã, and for the response to herbicides were conducted five trials of dose-response curves to the herbicide glyphosate, 2, 4-D, metsulfuron-methyl, flumioxazin and saflufenacil. In the emergency experiments it have been demarcated two areas side by side. One kept uncroped and another subjected to the usual crop of the total area. In both areas, treatments were represented by twelve months of the year to carry out the count of emerged plants for each month. The samples to estimate the seed bank were collected in the month of August in each of the twelve portions of the area kept uncroped in the depths of 0 to 5 cm and 5 to 10 cm. In trays kept in a greenhouse (UFSM), counts were made of emerged plants, every 15 days for 150 days. For dose-response curves were established doses and represents the division multiple of the recommended dose of herbicide for similar species as 0; x / 8; x / 4; x / 2; x; 2x; 4x; 8x. For glyphosate x = 1440 g ha-1, 2,4-D x = 670 g ha-1, metsulfuron x = 2.4 g ai ha-1, flumioxazin x = 50 g ai ha-1 and saflufenacil x = 35 g ai ha-1. Herbicide treatments were applied to plants with 8 to 10 leaves. The variables were visual assessment of control (%) (range 0-100) at 3, 7, 14, 21 and 28 days after treatments and the mass of green and dry matter of roots and shoots, producing the total mass and relative, by its expression as a percentage of treatment without herbicide to 28 days. The results show that E. mollis emerges during all months of the year, with major emergencies in the months of November, February and May. But the seed bank pointed to the presence in the average of all samples of 400 seeds m2 of E. mollis in the 0 to 5 cm and inexpressive 5 to 10 cm. There was a weak correlation between the emerged plants and seed bank, proving to be the most intense emergency probably due to soil temperature for the months of November, February and May. It can be suggested that emergency peaks coincide with the time of implantation of cultures and thus represent the best opportunities to make up the control. The results found with the curves show that glyphosate and 2,4-D are not efficient in the control and can not conclude on the efficiency metsulfuron, flumioxazin and saflufenacil.