Four steinernematid strains, Steinernema carpocapsae All strain, S. carpocapsae Umeå strain, S. feltiae Lie strain, and S. feltiae strain 27, were evaluated in laboratory and field tests as potential agents for the control of the black army cutworm, Actebia fennica (Tauscher). Although each of the six instars was susceptible to attack, incidences of infection were highest and generally over 60% for the third, fourth, and fifth instars when exposed to 100 infective juvenile nematodes in petri dishes. Fifth-instar larvae exposed for 1 week to soil containing 4000 infective juveniles in a 1:1:1 mixture of the L1c, All, and Umeå strains were most frequently infected with the L1c strain when reared at 10 and 12 °C and with the All strain when reared at 14 and 16 °C. One hundred thousand infective juveniles of the L1c, All, and Umeå strains and strain 27, alone and in various combinations, and applied by either a spray or soil-plug inoculation, killed black army cutworm larvae caged in the field for 1 week with treated black spruce seedlings and provided protection of current and 1 -year-old foliage. Treatments that included strain 27 provided the best protection when daily mean soil temperatures were 7–11 °C in comparison to treatments that included the Umeå or All strains, whereas treatments that included the All strain as a component appeared to be more effective than treatments containing the L1c and Umeå strains when daily mean soil temperatures were 16–17 °C.