TOWARDS PREDICTING PESTICIDE DEPOSITION FROM PLANT PHENOLOGY - A STUDY IN SPRING BARLEY

The relationship between crop architecture and spray interception was investigated in spring barley at two developmental stages. Height and outer surface area were determined for stems, leaves and ears, when pr esent. To trace the droplet interception by the crop a fluorescent dye was used. To avoid difficulties in measuring spray deposition on plan t surfaces, the non-intercepted pesticide at different heights in the air between the plants was determined from the deposit on glass strips placed horizontally at different crop strata. A regression model was used to relate the glass strip measurements to the plant surface measu rements. Analysis of the crop architecture indicated that the position and size of the leaves, the stem thickness and stem surface could all be described as a function of the height of the flag leaf. Analysis o f deposition measurements showed that stems, leaves and ears all contr ibuted significantly to spray interception, which correlated in a log- linear way with plant surface. The plant surfaces of stems, leaves and ears showed no significant differences in the fractions of droplets t hat were captured per unit of surface area, which fraction was indicat ed as the 'k value'. This showed that the droplet interception in spri ng barley could, in principle, be modelled using a single coefficient. As a one-parameter model would restrict interpretability and comparab ility of the present results with other studies, the approach with sep arate k values was nevertheless preferred when analysing the depositio n pattern in the crop and on the soil. The prospects of using crop hei ght as the main model parameter for crop architecture in future predic tions of pesticide deposition in cereals are discussed. (C) 1998 SCI.