Disease resistance is often associated with compromised plant growth and yield due to defense‐growth tradeoffs. However, key components and mechanisms underlying the defense‐growth tradeoffs are rarely explored in maize. In this study, we find that ZmSKI3, a putative subunit of the SUPERKILLER (SKI) complex that mediates the 3′‐5′ degradation of RNA, regulates both plant development and disease resistance in maize. The Zmski3 mutants showed retarded plant growth and constitutively activated defense responses, while the ZmSKI3 overexpression lines are more susceptible to Curvularia lunata and Bipolaris maydis. Consistently, the expression of defense‐related genes was generally up‐regulated, while expressions of growth‐related genes were mostly down‐regulated in leaves of the Zmski3‐1 mutant compared to that of wild type. In addition, 223 differentially expressed genes that are up‐regulated in Zmski3‐1 mutant but down‐regulated in the ZmSKI3 overexpression line are identified as potential target genes of ZmSKI3. Moreover, small interfering RNAs targeting the transcripts of the defense‐ and growth‐related genes are differentially accumulated, likely to combat the increase of defense‐related transcripts but decrease of growth‐related transcripts in Zmski3‐1 mutant. Taken together, our study indicates that plant growth and immunity could be regulated by both ZmSKI3‐mediated RNA decay and post‐transcriptional gene silencing in maize.