Maize is the most commonly grown field crop in the Republic of Croatia, where weeds are the main cause of yield loss. Today, weed species in maize are controlled mainly by the use of herbicides. However, considering the European Commission's "European Green Deal strategy," which aims to reduce the use of all pesticides by 50% by 2030, it is necessary to explore other ways to control agricultural pests. In previous research, phenolic acids have shown their potential as an alternative to pure herbicides, particularly vanillic, p-coumaric and ferulic acids, which inhibit the growth and early development of Ambrosia artemisiifolia, the most common broadleaf weed in maize. Since it is not possible to obtain a satisfactory inhibitory effect on weed species with phenolic acids alone, it is necessary to study their application simultaneously with reduced doses of herbicides. Therefore, the objective of this study is to determine the selective effect of vanillic acid in combination with various reduced doses of the herbicide mesotrione. In the laboratory, maize seeds were treated under in vitro conditions with a reduced dose of mesotrione and combinations of linearly decreasing doses of herbicide containing the phenolic compound vanillic acid. Subsequently, germination, radicle and coleoptile length, and dry weight of maize seedlings were determined. The research results show that maize is selective to all applied herbicide doses in combination with vanillic acid under in vitro conditions. For all measured parameters, no greater inhibition was observed when the combination of herbicide and vanillic acid was applied compared to when the herbicide was applied independently.