EFFECTS OF APPLICATION METHOD ON THE PERFORMANCE OF SOME SOIL-APPLIED HERBICIDES .2. FIELD STUDIES

Plots sown with a range of test species [Alopecurus myosuroides, Stellaria media, Chenopodium alba, Avena fatua, Lolium perenne, Raphanus raphanistrum] were treated with chlortoluron, nitrofen, propyzamide or terbutryne applied at several doses either by rotary atomizer (30 l ha-1), conventional hydraulic nozzle (250 l ha-1) or dribble bar (with orifices spaced at 2 cm intervals) (520 l ha-1). The performance of chlortoluron, propyzamide and terbutryne was similar with all the methods used, regardless of soil and weather conditions. Vertical movement in the soil was similar for each application method. Horizontal variability following dribble-bar application was measured for chlortoluron and was very large across short distances, but weed control was as uniform as with the other application methods. In a further experiment, the phytotoxicity of chlortoluron applied by each of the 3 methods was less in a seed bed prepared by minimum tillage following straw burning than in a plowed and cultivated seed bed. Activity following minimum tillage and straw baling was intermediate. This difference in phytotoxicity probably resulted from greater adsorption in the surface layers of the minimal cultivation treatments.