Behaviour of glufosinate and glyphosate in Ambrosia artemisiifolia
Ambrosia is reported to have a tendency to be xerophile (resistant to drought) and is even sometimes described as halophyte (resistant to a certain concentration of salt in the soil). One characteristic of drought resistant species is to have a cuticule which is not very permeable to water. This lipidic structure is in fact a barrier to hydrophilic substances and water. Previous studies have shown that glufosinate and glyphosate seem to penetrate very rapidly in A. artemisiifolia even though these herbicides present important hydrophilic characteristics. The foliar epidermis of A. artemisiifolia and the behaviour of these herbicides have therefore been studied to understand this paradox. Both leaf surfaces exhibited 3 types of trichomes, varying by their size and shape. Epicuticular waxes appeared amorphous, which may explain the high levels of spray retention. Glufosinate and glyphosate were rapidly and almost completely taken up by A. artemisiifolia leaves; half maximum uptake was nearly reached after 5 and 3 hours respectively. The longest trichomes were stained with AgNO3, indicating the presence of hydrophilic domains, which possibly facilitated the uptake of these very hydrophilic herbicides. Both were ambimobile, with 10-15% translocation out of the treated leaves. Glufosinate was mainly directed towards the apical developing tissues, with low amount reaching the roots. Glyphosate was directed towards the apical developing tissues and the roots. The sensitivity of A. artemisiifolia to glufosinate and glyphosate can be explained by high spray retention, rapid and important foliar uptake, and appreciable migration out of the plant parts hit by the spray.
Sources
Gauvrit C, Grangeot M, Chauvel B (2006) Les paradoxes du glufosinate et du glyphosate – comportement dans l’ambroisie à feuille d’armoise. Phytoma - La Défense des Végétaux no. 591, 8-11