High-Temperature Influences Plant Bio-Stimulant-like Effects of the Combination Particle Film-Forming Materials-Foliar Fertilizers on Apple Trees

Particle film forming materials were introduced as a solution to reduce the effects of excessive solar irradiation on plant photosynthesis. Covering plant leaves with particle films leads to plant bio-stimulant-like effects: increased protection against abiotic stress and increased fruit quality. We used zeolites and diatomaceous earth carriers for foliar fertilizer, known for their application as particle film-forming material. The aim of this paper was to investigate the plant bio-stimulant-like effects of this combined two-in-one product on the yield of apple trees and their photosynthetic pigments and fruit quality. The experiments were conducted for two years, 2021 and 2022, which had different agroclimatic patterns: 2021 had a deficit of precipitation, whereas 2022 was warmer by more than +4.8 °C compared to the recorded average temperature. Applying particle film-forming material and foliar fertilizer reduces the degradation of the photosynthetic pigments by drought and excessive solar radiation by 25–30%. In the year with a deficit of precipitation there was an increased yield by an additional 11.56–12.38% and the fruit quality similarly increased. Such effects of these combined two-in-one products were limited in 2022 as the temperature was higher than normal by several degrees.