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 efficac