The effect of application techniques on field-scale efficacy: can the use of entomopathogenic nematodes reduce damage by western corn rootworm larvae?
Field studies on the efficacy of entomopathogenic nematodes as biological pest control agents in field crops and over multiple seasons are rare. In the present study, we investigated the efficacy of Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae) at reducing maize root damage caused by the larvae of the western corn rootworm Diabrotica virgifera virgifera LeConte (Coleoptera: Chrysomelidae). The study consisted of 21 field-scale experiments in Hungary conducted between 2004 and 2007. Key factors behind successful control, such as application techniques, nematode dosage, soil environment and rainfall, were analyzed. Five of the six tested techniques for applying the nematodes using readily available farming machinery resulted in a reduction of root damage, as well as subsequent plant lodging. According to damage rating with the Iowa 1-6 scale, damage was reduced by 3-18%. According to the 0.00-3.00 node injury scale, damage was reduced by 14-54%. Approximately 7-62% of plant lodging, and thus direct yield losses as a result of in-harvestability, was prevented. An increase in nematode dosage and/or an increased rainfall during the period of applications increased the efficacy of H. bacteriophora at reducing root damage. Except for the obvious effect of moisture, the soil environment had little measurable influence on nematode efficacy. The present study demonstrates the potential for field-scale nematode application to significantly reduce damage caused by D. v. virgifera larvae. It is recommended that the method of agent application should be selected on a case-by-case basis considering the efficacy data presented here, the available application machinery and its associated costs.