Entomopathogenic nematodes (Steinernema spp. and Heterorhabditis bacteriophora) and a fungus Beauveria brongniartii for biological control of the white grubs, Ectinohoplia rufipes and Exomala orientalis, in Korean golf courses

Three species of entomopathogenic nematodes, a combination of two nematode species, an entomopathogenic fungal species, and a combination of a nematode and fungal species were evaluated against the white grubs Ectinohoplia rufipes and Exomala orientalis (Coleoptera: Scarabaeidae) in the field. The nematodes were a commercial formulation of Steinernema carpocapsae (BioSafe) and S. glaseri from Dongrae and from Hanrim, and Heterorhabditis bacteriophora from Hamyang, Republic of Korea. The entomopathogenic fungus was Beauveria brongniartii, produced on Sabouraud maltose agar plus 1% yeast (SMAY), rice bran, or compost. The combination treatment was S. carpocapsae with H. bacteriophora or B. brongniartii. Field applications were made in August or September against third instars at a golf course infested with E. rufipes in Gyeongnam Province in 1991, and one in Pusan with E. orientalis in 1992 and 1993. In 1991, a significant reduction of 70.2 to 79.4% of E. rufipes larvae was observed in the nematode, fungal and chemical (fenitrothion) treatments compared with a 15.7% reduction in the control. In 1992, the E. orientalis larval population was reduced between 62.7 and 82.8% in the treatments compared to 10.7% in the control. In 1993, larval reductions in plots treated with nematodes (78.3 to 97%) and B. brongniartii propagated on rice bran (84.5%) were significantly better than in plots treated with B. brongniartii propagated on SMAY (63.6%) or compost (59.6%). Combining two nematode species did not enhance the efficacy compared to treatments with one nematode species alone, but combining S. carpocapsae with B. brongniartii produced on SMAY resulted in a significant increase in grub mortality over the application of the fungus alone produced on SMAY or compost. The high efficacy of the nematode and most fungal treatments was attributed to the close proximity of the white grubs to the soil surface which allowed for excellent pathogen-host contact and to favorable soil temperatures, sandy soil, post irrigation application and/or rain and a minimal thatch layer in the turfgrass.