Effect of the volume rate of application on the glasshouse performance of crop protection agent/adjuvant combinations

The effects of volume rate of application on the glasshouse performance of three recently developed crop protection agent/adjuvant combinations are discussed. High volume rates of application on easy-to-wet foliage, such as potato (Solanum tuberosum, L.) caused reduction of the adjuvant-enhanced performance of dimethomorph seen at low volume rates. These reductions were largely attributable to relatively lower spray retention with spray drop coalescence and run-off being observed, particularly at the higher adjuvant rates. On difficult-to-wet foliage (wheat, Triticum aestivum, L.; oat, Avena sativa, L.) two different effects were seen. With a metconazole formulation/'Dobanol' 91-6 combination on wheat, no systematic changes in performance were observed with change in volume rate. With a flamprop-M-isopropyl formulation/'Dobanol' 25-7 combination, statistically significant increases in performance were seen with increasing volume rate. In both cases the observations can be explained as the result of a combination of interacting factors involving spray pattern, spray deposition and, by inference, foliar uptake of the crop protection agent, the proportions of which differed between the two cases. It is suggested that the effect of volume rate of application on performance of adjuvant-containing formulations is investigated on easy-to-wet foliage to determine the upper limits and on difficult-to-wet foliage to determine any variation in performance that may occur. Such information will guide the design of field trials and may aid interpretation of field results.