LAUSR

Background and Aims Spring drift of herbicides can have devastating consequences on grapevines. The impact of 2,4‐dichlorophenoxyacetic acid (2,4‐D), dichloro‐2‐methoxybenzoic acid (Dicamba), 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA) and glyphosate exposure on reproductive and vegetative development was investigated. Methods and Results Simulated herbicide drifts were applied to potted vines at the cessation of flowering. Leaf gas exchange and biomass, root structural biomass and carbohydrate reserves, fruit yield and compound bud necrosis were assessed, along with berry composition, including the primary metabolites, at fruit maturity. Fruit yield was reduced by 2,4‐D without any detriment to most aspects of berry composition. While root structural development was curtailed by 2,4‐D, Dicamba and MCPA, none of the herbicides altered the reserve level of root total non‐structural carbohydrates. Primary bud necrosis was evident following 2,4‐D and Dicamba exposure, especially in younger buds. Conclusions Exposure to 2,4‐D may be particularly damaging to fruit yield during the current season because of an increased risk of bunch necrosis. Bud fruitfulness can be impaired by 2,4‐D and Dicamba because of the increased potential for primary bud necrosis. Significance of the Study Auxin‐type herbicides can limit fruit yield during the current and next season. Compared to cane pruning, spur pruning may minimise the detrimental effects of these herbicides on fruitfulness.