FOLIAR UPTAKE OF PGRS: BARRIERS, MECHANISMS, MODEL SYSTEMS, AND FACTORS

Many systemic agrochemicals such as plant growth regulators (PGRs) are foliar applied. Consistent performance of foliar-applied PGRs requires maximized uptake. In this review, foliar uptake of active ingredients (ai) is discussed including: the mechanism of penetration along cuticular and stomatal routes, the concepts of lipophilic and polar pathways, and techniques commonly employed to investigate foliar uptake. We compare published data on isolate cuticle finite dose penetration of lipophilic naphthalene acetic acid (NAA) and hydrophilic aminoethoxyvinylglycine (AVG) as model compounds. We discuss the effects of environmental factors such as temperature and humidity and the importance of penetration from the droplet residue/deposit. Finally, Five Generalized Rules of Finite Dose Penetration of isolated tomato fruit cuticles are presented based on previous research on S-abscisic acid (ABA), AVG, 6-benzyladenine (6BA), NAA, polyethoxylated (Triton X) surfactants, and urea.