Response of Malus x domestica Borkh to metamitron and high night temperature: Effects on physiology and fruit abscission

•Increased nighttime temperature and metamitron application, per si, retarded fruitlet growth rate by 30%, reduced sucrose and sorbitol leaf content and enhanced abscission, in a similar way.•The greatest reductions in sucrose and sorbitol were caused by metamitron combined with higher nighttime temperature, followed by the strongest thinning efficacy and fruit size improvement.•Metamitron inhibit photosynthesis and reduced carbohydrate (CH) production whereas high nighttime temperature increased CH consumption likely due to greater respiration rates.•Enzyme related with oxidative stress control were moderately enhanced under the combined use of metamitron and nighttime temperature.