Species combinations, split applications, and syringing to optimize the efficacy of entomopathogenic nematodes against Agrotis ipsilon (Lepidoptera: Noctuidae) larvae in turfgrass

Abstract

Entomopathogenic nematodes, especially Steinernema carpocapsae, can provide good control of the larvae of the black cutworm, Agrotis ipsilon (Hufnagel), a cosmopolitan pest of golf course turfgrass. However, these biocontrol agents do not meet the high expectations for level and consistency of control by golf course managers on the affected high-profile areas. We explored three different approaches to further improve nematode performance. Combinations of S. carpocapsae with two other nematode species, S. feltiae or Heterorhabditis bacteriophora, did not improve control rates compared to S. carpocapsae alone. Syringing (i.e., light irrigation applied twice daily during hot weather) improved S. carpocapsae efficacy by on average 8% and also significantly reduced control variability (mean 78%, range 75–87%) at 109 nematodes per ha. The beneficial effect of syringing on S. carpocapsae performance can in part be ascribed to the improved persistence of the IJs in the syringing regime. The most effective approach to improve S. carpocapsae efficacy was through splitting applications into two applications at half rate applied 3 days apart. This improved efficacy by 13% on average while significantly reducing control variability (mean 84%, range 80–92%) at a rate of 109 nematodes per ha. At the generally recommended rate of 2.5 × 109S. carpocapsae per ha, split applications and syringing should consistently provide black cutworm control of 90% or higher and could make this approach competitive with synthetic insecticide use.