Background Boron (B) and silicon (Si) are fundamental for brassica nutrition, and in some cases, they have potential as an insecticide. Plutella xylostella (L.) (Lepidoptera: Plutellidae), one of the most economically important agricultural pests, is difficult to control due to the resistance to insecticides and the absence of alternative control methods. Results Cauliflower leaves sprayed with Si and B showed a higher concentration of the beneficial element and micronutrient, respectively. When evaluating the firmness of the cauliflower leaves, it was found that the plants with leaf sprayings of Si and B did not differ statistically from each other. However, they showed an increase in firmness, in relation to the plants of the control treatment. Leaf spraying of Si and B on cauliflower did not influence the number of eggs/female. The attractiveness index showed that both Si and B applications stimulated the presence of second instar larvae, being more stimulating in relation to the control treatment. However, the use of Si and B in isolation showed a positive result, since it caused high mortality in diamondback moth larvae compared to the control treatment. Conclusion The application of both foliar fertilizers positively affects the attractiveness index of the larvae, being attractive; however, both Si and B caused high mortality (~80%). The results showed that Si and B have the potential to control P. xylostella and serve as a basis for alternative pest management in brassica crops. © 2022 Society of Chemical Industry. The application of boron (B) or silicon (Si) increase B or Si leaf concentration, leaf firmness, attractiveness index and larval mortality, and decrease oviposition preference.