Use of different doses of glyphosate to control invasive plants: Bidens pilosa, Commelina benghalensis, Digitaria insularis, Ipomoea grandiofolia and Tridax procumbens

Glyposhate is among the most widely used herbicides in Brazil and worldwide and has a broad spectrum of control, low toxicity, non-selective, and systemic action. In Brazil, it has been increasingly consumed after its release to be used in plants with tolerance to the product; however, excessive use has contributed to select resistant or tolerant weed species. Our goal was to evaluate the efficiency of weed control by using glyphosate in a growth chamber at different doses, periods of applications, and weed species. The experimental design was completely randomized – factorial scheme 7 x 5 – by assessing seven doses of glyphosate: 0; 720; 960; 1200; 1440; 1680, and 1920 g ha-1 i.a., in five weeds: black picket, bitter grass, bull herb, viola string, and ragged, with five repetitions. The weeds were sowed in polyethylene pots with three plants per pot. Assessments of dry biomass were conducted after 7, 14, and 21 days of application (DAA) with the treatment of glyphosate in scores from 0 to 100%. We concluded that the herbicide was efficient at controlling the black picket and bitter grass species as 100% of the weed plants 14 DAA died with the doses of 720 g ha-1 i.a. Doses of glyphosate required to reach indices of control above 915 were 1680 g ha-1 i.a. for ragged, 960 g ha-1 i.a. for bull herb, and 1440 g ha-1 i.a. for viola string at 21 DAA – since these are considered hard to control. It is recommended to apply 1440 g ha-1 i.a. of glyphosate for an effective control over 80% of all invasive plants assessed at 21 DAA,.