AbstractPenetration of four herbicides (atrazine, diclofop‐methyl, dinoseb and glyphosate‐mono(isopropylammonium) salt) was followed through isolated pear leaf cuticles into agar and across intact cuticles of Argenteum (ARG) mutant pea leaves from monosized droplets (300 μ diam.) during 48 h following application. Penetration into pea leaves ranged from low for glyphosatemono(isopropylammonium) (5 of amount applied) and atrazine (14) to rapid for dinoseb (91) and diclofop‐methyl (82). A major proportion (90) of the dinoseb retained in the tissues underlying the site of droplet application migrated across the cuticle and the epidermal layer of cells. In contrast, only a small proportion (13) of the dinoseb entering the leaf was transported to the tissues surrounding the treatment zone. Corresponding values for diclofop‐methyl were 61 and 4 respectively. Initially, dinoseb also penetrated rapidly through isolated pear leaf cuticles, 36 of the applied dose being recovered in an agar receiver disc 4 h after treatment, but subsequent uptake was slower. Penetration of glyphosate‐mono(isopropylammonium) also decreased after 4 h whereas atrazine and diclofop‐methyl diffused steadily through isolated cuticles up to 216 h after treatment. The incorporation of ‘Tween 20’ or ‘Agral 90’ (1 g litre−1) into the formulation reduced the penetration of glyphosate‐mono(isopropylammonium) through iso
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