Herbicidal activity of Tunisian plant extracts against various weeds

Abstract

In agricultural systems, weeds can dramatically reduce crop yields (by the constant competition for water and nutrients) and interfere with plant functions to suppress their growth causing huge economic losses.Yield losses can reach up to 34% in crops. Plant extracts are known since a long time to have phytotoxicity potentialities and could be used as new natural compounds with bioherbicide activities. The study began with the selection of ten plant species suspected to be phytotoxic due to their wealth of phenolic, terpene and alcaloid compounds, such as flavonoids and phenolic acids coumarins. Then, three weeds were selected from Maghreb and European weeds as models (Phalaris minor, Sylibum marianum and Trifolium incanatum). Aerial plant materials were grounded and macerated with methanol for 24H. Methanol was then eliminated along rotavapor. The yield of plant extract varied between 5.29% and 29.71 % following the species. The essential oil was extracted by hydrodistillation using a Clevenger type apparatus (with a yield of 1.2%). Methanol extracts and the essential oil were then tested for their herbicidal activity in post-emergence assays against the three weeds species.The most active extracts were selected and formulated to increase their efficiency. Post-emergence bioassays consisted in spraying each extract at 3 concentrations (7500, 20000 and 340000 ppm) at 2 leaves stage . Pelargonic acid was used as commercial positive control at 34000 ppm. After 7 days on incubation in greenhouses, results showed that E6, presented poor phytotoxicity against three weeds at 7500 and 20000 ppm. However, E6 caused total wilting and several leaf blight against Phalaris minor and Trifolium incanatum and sever necrosis against Sylibum marianum. At that higher concentration of 34000 ppm. , the extracts E3 and E8 and the essential oil appeared also phytotoxic. The three extracts and the essential oil were selected for the formulation. After formulation to enhance the distribution, the coverage and the penetration of the active molecules at 34000 ppm, E3, E6, E8 and essential oil presented a high herbicidal activity compared with the extracts without formulation. E6 with the formulation has completely punctured Trifolium incanatum and suppressed growth of Phalaris minor and Sylibum marianum. The results of this study reveal that plant extracts, after formulation, are more effective in inhibiting weed growth. The strong weed suppressive ability of formulated E6 therefore offers interesting possibilities as an effective natural environment-friendly approach for weed management.Lutte Biologiqu