Herbicides in forest restoration: Selectivity and adequate dose as key factors for the management of Urochloa decumbens

Forest restoration in the Atlantic Forest is challenged by the invasion of Urochloa decumbens, which suppresses native species and hinders ecosystem recovery. This study evaluated the selectivity and optimal doses of Glyphosate and Haloxyfop to enhance invasive control while minimizing impacts on native species. Ten native tree species were tested under four increasing doses of Glyphosate, ranging from 720 to 2880 g a.i. ha⁻¹, and Haloxyfop, ranging from 30 to 90 g a.i. ha⁻¹. We assessed survival, growth, biomass allocation, and photosynthetic efficiency. Glyphosate suppressed U. decumbens by more than 90 % from 60 days after application. However, it severely affected native species, reducing survival to 60 %, biomass by up to 80 %, and photosynthetic efficiency to an Fv/Fm ratio of 0.05. Haloxyfop was more selective, maintaining 96 % survival and preserving biomass and photosynthesis, but its effectiveness in controlling U. decumbens declined from 67 % at 30 days to 13 % at 120 days. The optimal dose of Glyphosate for balancing invasive control and native species conservation was 171 g a.i. ha⁻¹, which reduced U. decumbens cover by 55 % while limiting biomass loss to 11 %. For Haloxyfop, the optimal dose was 90 g a.i. ha⁻¹, achieving maximum invasive control without affecting native species' biomass. Our findings demonstrate that integrating herbicide selectivity with optimized doses can effectively control invasive grasses while preserving native species, providing a valuable strategy for ecological restoration.