Uptake into and local translocation within leaves sprayed with radiolabelled glucose and fourteen agrochemicals dissolved in aqueous acetone has been measured for four species (maize, rape, strawberry and sugar beet). Uptake during droplet drying (2‐3 min after application) was small (mean value 4% of applied compound) and similarly only small amounts of compounds were found in the epicuticular wax 24 h after application. Total uptake into the leaf ranged from 1‐97% at 24 h, depending on compound and on species. Enhancement of uptake by addition of a non‐ionic surfactant was very variable. Regression analysis and graphical plots showed that uptake was inversely related to melting point, except into sugar beet, and for this species and for strawberry, uptake was also inversely related to water solubility. Both uptake and translocation passed through a maximum with increasing partition coefficient in most cases, with optimum values of log (partition coefficient) of c. 0 and 1.5‐2.2 respectively. The uptake of the four polar compounds used also appeared to be affected by their hygroscopicity and state of ionisation.

The time course of uptake has been determined for seven poly(oxyethylene) surfactants, and one anionic surfactant (sodium dodecyl sulphate), into the leaves of wheat plants grown in a phytotron. Uptake was relatively rapid during an initial period of 24 h for six of the eight surfactants; after this period, the uptake rate was lower, and total uptake after 48 h was in the range 80‐91% for those six surfactants. The other two compounds, sodium dodecyl sulphate and cetostearyl alcohol‐22EO condensate (hexadecan‐1‐ol/octadecan‐1‐ol ethylene oxide condensate; average number of ethylene oxide units 22) were barely taken up at all. The observed time course for uptake was consistent with a complex process based on more than one rate‐determining process. The physical properties of the surfactants are discussed in relation to their observed uptake behaviour. The surfactant deposit areas, measured by microscopy, were concluded to be not particularly relevant in interpreting the uptake results. Uptake was not related to surfactant chain length, but the physical form of the hydrated surfactant on a leaf surface appeared to influence uptake behaviour.

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The uptake from foliar deposits of 10 14C‐labelled compounds into each of 10 species of field‐grown plants was measured 26 h after deposition by combustion of leaf tissue after removal of surface deposits. The compounds, which included eight pesticides, covered a wide range of lipophilicity and each was formulated in the same way; they were applied as droplets with a microsyringe. Uptake varied greatly between the species. All compounds were taken up well into maize and Xanthium pennsylvanicum, whereas relatively little entered the leaves of apple or orange. Uptake into the six other species varied according to the compound. Amongst the eight non‐polar compounds, no relationship between the rate of uptake and molecular size was discerned, and only in X. pennsylvanicum was uptake related to the partition coefficient and water solubility. Considering all the compounds, weak relationships were observed between molecular cross‐sectional area and uptake into four species. The range of the uptake rates (×130) was small compared with those of octan‐1‐ol‐water partition coefficients (×1010) and water solublities (×107) shown by the 10 compounds. Possible reasons for the absence of correlations between the uptake and the molecular properties considered are discussed. The results are consistent with either separate routes of cuticular entry for non‐polar and polar compounds, or a common route for both types of compound. The generally poor uptake by apple and orange leaves, which may be related to their thick cuticles, highlights the need to develop special formulations to optimise uptake into these species.

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