Relationships between leaf anatomical features of Arundo donax and glyphosate efficacy.
Cuticle thickness is known to affect the amount of active ingredient that reaches the target site of a post emergence herbicide and consequently its efficacy. So, this work aimed to relate glyphosate efficacy with the thickness of leaf cuticle of young and mature leaves of Arundo donax. Glyphosate was applied at different development stages of the invasive species, in spring, summer and autumn at the concentrations of 0.675; 1.350 and 2.025 g L-1. Cuticle thickness of mature and young leaf blade and leaf sheath was measured on transverse sections by light microscopy. Despite the significant differences in the cuticle thickness between young and mature leaves, this did not seem affect the efficacy of glyphosate uptake since no significant differences were observed between young and mature leaves glyphosate treatments. But herbicide efficacy was dependent of the plant development stage. Higher efficacy of glyphosate was recorded when plots were sprayed at the end of October (flowering) compared to end April and mid June applications. Mortality of giant reed was higher than 90% one year after treatment only in autumn treatments. This result suggests that other mechanisms are involved, probably the reserves carrying over to rhizomes, on herbicide efficacy.