Organic foliar fertilisers containing calcium, phosphorus, and plant extracts for the potential control of some insect pests of Brassica oleracea var. capitata L.

The cabbage whitefly (Aleyrodes proletella L.; Hemiptera: Aleyrodidae), the diamondback moth (Plutella xylostella L.; Lepidoptera: Noctuidae), and the cabbage aphid (Brevicoryne brassicae L.; Hemiptera: Aphididae) are responsible for the most significant losses in cabbage (Brassica oleracea var. capitata L.) cultivation. In this study, two commercial foliar fertilisers, Mitemine® (a calcium fertiliser) and D-Fense (a phosphorus and potassium fertiliser), and the insecticide Movento 100 SC (spirotetramat) were used to control these pests. In 2020, all treatments applied 6 times reduced pest infestations by approximately 60%–80% compared with the untreated controls. In 2021, a decrease in the number of treatments to 4 resulted in a 10%–20% reduction in effectiveness. Light and scanning electron microscopy revealed variations in the number and density of stomata, cuticle thickness, and leaf structure between the control and treatment groups. Anatomical evaluation suggested that the thickening of the cuticle and epidermis on the abaxial side of the leaves, including the vascular bundles – likely due to the calcium in Mitemine® – may be one of the mechanisms responsible for the observed decrease in the pest population density. The combination of D-Fense and Mitemine® did not significantly alter the effectiveness of Mitemine® against herbivores; however, this combination resulted in a more compact structure of the mesophyll, thicker abaxial epidermis inner cell walls, and a thick layer of cuticle on stomata surface. The findings indicate that foliar fertilisers containing calcium can enhance plant resistance to pests, offering a potential alternative to chemical pesticides in sustainable crop protection strategies.