Survivorship and development rates were determined for cohorts of noctuid larvae caged on irrigated and dryland ‘Braxton’ soybean plants in the Delta of Mississippi. In September 1985, larval survival of fall armyworm,Spodoptera frugiperda(J. E. Smith), was higher in irrigated than in dryland soybean, although no differences were observed for rate of larval development. In July 1986, survival of fall armyworm and soybean looper,Pseudoplusia includens(Walker), was higher and development faster in irrigated than in dryland soybean, whereas no differences were observed for corn earworm,Helicoverpa zea(Boddie), during a period of high temperatures. In September 1986, survival and development rates were similar for these three species. In a study conducted with soybean planted in a nursery in July 1987, survival and rate of larval development of soybean looper, but not beet armyworm,Spodoptera exigua(Hübner), were positively correlated with canopy closure. Irrigation of soybean resulted in a cooler canopy environment or higher leaf water content or both. Irrigation increased survival (in the absence of predators) and optimized larval development of some noctuids, whereas the lack of irrigation had no effect or was favorable for larval development of other noctuid species.