Some aspects of absorption, translocation and metabolism of two foliar applied auxin herbicides in gorse (Ulex europaeus L.) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science at Massey University
Since Ulex europaeus is a problem scrub weed in New Zealand hill country, glasshouse and laboratory experiments were undertaken to study factors relating to the absorption of 2,4-D and picloram and the translocation and metabolism of picloram. Any one of these parameters may be limiting the effectiveness of picloram and other auxin herbicides in the field. Absorption was studied using in vitro and in vivo methods. Cuticular surfaces were studied using scanning electron microscopy and the contact angles of droplets were photographed using an optical microscope. Translocation patterns were observed using autoradiographs as well as by sectioning the plant and counting the distribution of radioactivity in each section. Metabolites were examined for by a radio chromatogram scan of tissue extracts separated by descending paper chromatography. The results obtained suggest that absorption is poor due primarily to the presence of a thick smooth layer of cuticular waxes. Environmental conditions at, and subsequent to, spraying are likely to affect absorption in the field. Drying of the spray deposits inhibits absorption; re-wetting a dried deposit with mist enhances absorption. Additives, especially surfactants and the inorganic salts KCN and Na2
HPO4, enhanced in vitro absorption. Information on the mechanism of absorption was gained from the response to light, temperature and concentration of herbicide. Picloram was readily translocated from the treated stem to the roots. Very little re-distribution of picloram occurred. Source-sink relationships occur. No metabolites could be detected from spines and stems. Stem tips and roots were not tested.