Suppression of plant-parasitic nematodes by application of live and dead infective juveniles of an entomopathogenic nematode, Steinernema carpocapsae, on boxwood (Buxus spp.)

Effects of live and dead (heat-killed) infective juveniles (IJs) of the entomopathogenic nematode Steinernema carpocapsae on nematodes associated with boxwood Buxus spp. were evaluated in field experiments during 1999 and 2000. Both living and dead IJs of S. carpocapsae were equally effective, causing more than 50% reduction in total populations of plant-parasitic nematodes relative to the control 15 and 30 days after treatment in both years. No significant differences were observed between reductions in populations of plant-parasitic nematodes following entomopathogenic nematode and chemical nematicide (ethoprop) treatments. In 2000, populations of Criconemella, Hoplolaimus, Longidorus, and Rotylenchus were significantly reduced in all treatments relative to the control 30 days after treatment. However, in 1999 these genera were unaffected by treatments even though total plant-parasitic nematode population was decreased. The population of Tylenchorynchus was significantly reduced in all treatments 30 days after treatment in 1999. Further, the population of Tylenchus was significantly reduced in ethoprop and dead S. carpocapsae treatments 15 days after treatment relative to the control whereas the population of Aphelenchoides was unaffected by these treatments in 1999. Live S. carpocapsae showed no significant effect on the population of both these genera either 15 or 30 days after treatment in 1999. No viable symbiotic bacteria were observed in the dead nematodes used in this study indicating that dead nematodes alone or dead nematodes in combination with dead symbiotic bacteria produced the suppressive effect. In contrast to the plant-parasitic nematodes, populations of non-stylet-bearing nematodes were not affected by the application of entomopathogenic nematodes. Although ethoprop reduced population of non-stylet-bearing nematodes relative to the untreated control 15 days after treatment in 2000, no significant differences were observed 30 days after treatment. These findings suggest that allelochemicals produced by dead or live nematodes and/or by their symbiotic bacteria may be selectively acting against plant-parasitic nematodes. Our results demonstrate that both live and dead infective juveniles of S. carpocapsae may provide a possible control strategy for plant-parasitic nematodes on boxwood.