Abstract: Apple rust and apple scab are leaf diseases that can significantly diminish apple production. This study aimed to develop a biocontrol strategy using a combination of traditional Chinese herbal medicine and potassium phosphite to manage these diseases. The efficacy of this combined treatment was evaluated on disease control and its impact on apple leaf growth. The results showed that the integrated approach provided control efficiencies of 61.65% and 73.00% against apple rust, and 90.91% and 98.85% against apple scab at 14 and 28 days post-final application, respectively. These rates were comparable to the application of difenoconazole 10% WG, while reducing the dosage of the Chinese herbal medicine and potassium phosphite by 10% and 24.92%, respectively, demonstrated a significant synergistic effect. The combined treatment also led to an increase in leaf area, thickness, and both fresh and dry weights, as well as enhanced levels of chlorophyll and amino acids. Additionally, it significantly boosted the activities of defense enzymes, including superoxide dismutase (SOD), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL), and lipoxygenase (LOX), with increases ranging from 83.73% to 503.45% over the control. The combination of Chinese herbal medicine and potassium phosphite could control the occurrence of apple rust and apple scab effectively, and improved the disease resistance of apple trees, showing great potential for green control of apple leaf diseases.

Key words: Chinese herbal medicine, potassium phosphite, apple scab, apple rust, control effect, enzymatic activity