Pseudostellaria heterophylla (or Taizishen in Chinese), a medicinal, edible, and ornamentalChinese herb, is seriously affected by leaf spot disease (LSD). Oligochitosan is a natural agricultural antibiotic that is produced via the degradation of chitosan, which is deacetylated from chitin;pyraclostrobin is a broad-spectrum and efficient strobilurin fungicide. In this work, the ability ofpyraclostrobin, oligochitosan, and their formula to manage P. heterophylla leaf spot disease and theirrole in its resistance, leaf photosynthesis, agronomic plant traits, root growth, and root quality werestudied. The results show that the joint application of oligochitosan and low-dosage pyraclostrobincould control LSD more efficiently, with control effects of 85.75–87.49% compared to high-dosagepyraclostrobin or oligochitosan alone. Concurrently, the application of this formula could more effectively improve the resistance, leaf photosynthesis, agronomic plant traits, root yield, and medicinalquality of P. heterophylla, as well as reduce the application of pyraclostrobin. This finding suggests that30% pyraclostrobin suspension concentrate (SC) 1500-time + 5% oligosaccharin aqueous solutions(AS) 500-time diluent can be recommended for use as a feasible formula to manage LSD and reducethe application of chemical pesticides.