The effects of application factors on the performance of MCPA, difenzoquat, paraquat and glyphosate have been studied in relation to very low volume, controlled drop size sprays. Factors studied were drop size, herbicide concentration, position of deposit on the plant surface, and surfactant concentration. Spray retention was measured on wild oat, radish and barley, comparing an application of around 20 l. ha-1 using 250 mum drops with a conventional spray of around 200 l. ha-1. More herbicide was retained with the low volume rate application, but a greater proportion of that retained with the conventional spray was on the young and erect plant parts. With MCPA and paraquat performance was unaffected by drop size between 200 and 400 mum, herbicide concentration or surfactant concentration. Glyphosate performance was not affected by drop size but was enhanced by higher concentrations of the herbicide. With difenzoquat, performance was impaired by higher concentrations and larger drop sizes due to necrosis at the site of treatment, which reduced entry and movement of the 14C-labelled herbicide. Evidence is given that stomatal guard cells are preferential sites of entry of exogenously applied chemicals, and it is suggested that this may contribute to the onset of necrosis by damage to the stomatal mechanism. Difenzoquat performance was also reduced by a low surfactant concentration. The effects of position of deposit were specific to each herbicide. On radish, paraquat was most effective when applied to the cotyledons whilst MCPA was most effective on the midvein of the foliar leaves, and glyphosate when applied to the foliar leaf laminae between veins. Paraquat and difenzoquat were most effective on younger leaves of wild oat and towards the lamina base, whilst leaf age did not influence the performance of glyphosate with this species.
|Date of Award||1980|