Uptake and distribution of [14C]metalaxyl by detached tobacco leaves

When the petioles of detached tobacco leaves (10–17 cm2) were incubated in aqueous solutions containing [14C]metalaxyl, uptake of the fungicide was dependent on the temperature and photoperiod. Detached leaves took up 78% more [14C]metalaxyl at 26°C than at 16°C. The rate of uptake in the light at 21°C was linear, but after an additional 20h in the dark, there was only twice as much fungicide in the leaves. Different sized leaves contained the same amount of fungicide per cm2 area. Uptake by detached leaves of the 14C‐labelled anilide lactones ofurace and RE‐26940 [2‐methoxy‐N‐(tetrahydro‐2‐oxo‐3‐thienyl)acet‐2′,6′‐xylidide] was similar to that of metalaxyl. At the concentration of metalaxyl (66 ng ml−1) that controlled blue mould (Peronospora tabacina) on detached tobacco leaves, the amount of fungicide in the leaves was found to be 7.25 ng. Autoradiography showed that the distribution of [14C]metalaxyl in detached leaves after incubation for 23h was uniform, although higher concentrations of the label were present in the smaller veins of the leaves.