ZNC is an ultrahighly active plant immune inducer extracted from the endophyte Paecilomyces variotii that can promote plant growth and enhance plant immunity. Our research aim was to further reveal the trade-off balance between plant growth and immunity by evaluating the mechanisms of ZNC on potato growth, yield, and priming immunity against the oomycete Phytophthora infestans indoors and under field conditions. ZNC sustained the balance between potato growth and resistance to Phytophthora infestans with ultrahigh activity. It induced ROS production, promoted plant growth, yield and quality parameters, enhanced the expression of IAA-related genes, and increased the absorption of N. Moreover, the flg22 and chitin signaling pathways contributed to the ZNC-mediated defense response. Irrigation with ZNC at one of two optimal concentrations of 1 or 10 ng/ml could enhance resistance against potato late blight and marketable yield. Spray application of ZNC onto potato plants significantly reduced the occurrence of potato blight disease and greatly increased potato yield in the field. In summary, ZNC, which is a new ultrahighly active plant inducer, is a kind of green agricultural input with high efficiency and low cost that has excellent potential in agricultural applications.