Glyphosate affects the susceptibility of non-target native plant species according to their stage of development and degree of exposure in the landscape

Abstract

Unsustainable agriculture is producing a great socio-ecological transformation in Latin America because it has expanded into areas occupied by native forests. Glyphosate is the most widely used herbicide, with severe ecotoxicological effects on non-target organisms. The aim of this study was to determine the effects of glyphosate on seedlings of 24 non-target herbaceous and non-herbaceous plant species present in forest relicts of Argentine Chaco. The effects of a gradient of glyphosate doses (525, 1050, 2100, 4200, and 8400 g ai/ha) were measured in seedlings of each species under greenhouse conditions. Seedlings were grown from seeds collected from native forest fragments of different sizes (assuming three different degrees of historical exposure to glyphosate in the landscape). Doses were applied at different stages of seedling development (five- and ten-weeks after emergence), and phytotoxicity, growth reduction, and sensitivity were measured. Glyphosate produced lethal or sublethal effects in all 24 species, some of which were very sensitive (>60 % of the species presented strong to severe growth reduction with ¼ of the dose used on crops). The greatest toxicological effects were related to early stage of development, herbaceous species, and low historical exposure to glyphosate. According to the species sensitivity distribution, the drift-dose to protect 95 % of the plant species that occur in larger forest fragments should not exceed 5 % of the dose commonly used on crops. These results suggest that the current weed management linked to glyphosate-resistant crops could lead to a gradual loss of biodiversity in the landscape. Concurrently, selection of glyphosate-tolerant biotypes in some non-target species could represent a very problematic cycle for the current model of industrial agriculture. Some alternatives for weed control are proposed.