THE INFLUENCE OF FORM OF DEPOSIT ON THE PHYTOTOXICITY OF MCPA, PARAQUAT AND GLYPHOSATE APPLIED AS INDIVIDUAL DROPS

MCPA [4-chloro-2-methylphenoxyacetic acid] paraquat and glyphosate were applied as individual drops (200-400 .mu.m) to pot-grown plants of radish (Raphanus sativus) or wild oat (Avena fatua), using concentrations appropriate to very low volume applications of these herbicides. For a given dose per plant, herbicide activity was unaffected by concentration of MCPA or paraquat but was enhanced as the concentration of glyphosate was increased. The activity of all 3 herbicides on both species was affected by variation of the site of application but not by drop size. On radish the greatest activity resulted when paraquat was applied to the cotyledons, glyphosate to the interveinal areas of true leaves and MCPA to the veins of true leaves. This is discussed in relation to herbicide mobility and local toxicity following applications at high concentration.