Entomopathogenic nematode application against root-damaging Diabrotica larvae in maize: what, when, and how?

Abstract: Due to restrictions of neonicotinoid seed coatings and due to the high toxicity of tefluthrin-based soil insecticides, biological control solutions have been developed against the maize-root feeding larvae of the western corn rootworm (Diabrotica virgifera virgifera, Coleoptera: Chrysomelidae). Commercially mass-produced entomopathogenic nematodes of the species Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) had been registered against the larvae of D. v. virgifera in a number of countries. However, their use on a larger scale in field crops like maize is still limited. Whilst laboratory experiments and plant-scale field experiments have shown high control efficacies by those nematodes, field-scale trials by farmers lead to more variable results. We herewith summarise results of 22 field-scale trials implemented with farmer machinery between 2005 and 2018. In all field trials, nematodes were applied as fluid stream sprays into the sowing furrow after seed placement. This is currently the most common and economic application method. Results showed that nematodes usually appeared as effective as, or better than standard pesticides at reducing D. v. virgifera populations, and usually similarly effective or occasionally slightly less effective at preventing heavy root damage. Findings support a nematode-based solution for the biological control of D. v. virgifera larvae in maize fields as one among the alternative options to synthetic insecticides.