Several reports indicate that nematodes can be used to control Japanese beetle in turf, but many questions remain about how much irrigation is necessary, the effect of soil temperature on efficacy, and what rates to use.
Nematode efficacy is greatly influenced by irrigation. In previous studies, the efficacy of Heterorhabditis bacteriophora was improved by daily irrigation vs. watering at 2 to 10 day intervals. Similar improvements were seen with steinernematid nematodes when the turf was watered before and after treatment. Several strains of Steinernema glaseri did not control beetle larvae when they were applied without posttreatment irrigation, but the nematodes were as effective as chemical controls when they were watered in with 1/8 inch of irrigation after treatment. Surfactants do not seem to provide additional control.
Soil temperature is another important factor affecting nematode efficacy. Average parasitization is ~80% when soil temperatures are from 70° to 86°F, but is less than 40% when temperatures are less than 60°F.
The minimum rate needed to reduce grub populations below a threshold of 8 per ft2 appears to be between 1 and 2 billion per acre, with the higher rate giving greater consistency and better control. However, a greater degree of control can be achieved by applying more S. glaseri per acre. In autumn field trials in Rhode Island the greatest reduction in larvae occurred where S. glaseri was used at 8 billion per acre and irrigated daily with inch of water for 14 days. Greater control may be achieved with lower rates if nematodes are applied against earlier instars.
Yeh, T. and S. R. Alm. 1995. Evaluation of Steinernema glaseri (Nematoda: Steinernematidae) for biological control of Japansese and Oriental beetles (Coleoptera: Scarabaeidae). J. Econ. Entomol. 88(5): 1251-1255.
Nematode Strains and Species Vary in Control of Japanese Beetle
Entomogenous nematodes vary in their activity against beetle grubs partly because of differences in their host-finding behavior. Steinernema carpocapsae uses an ambush strategy to attach to and parasitize moving hosts--so it is usually ineffective against a sedentary, subterranean pest like Japanese beetle. In contrast, both S. glaseri and Heterorhabditis bacteriophora use a cruising strategy to locate hosts and tend to be more effective against sedentary pests.
Unfavorable field results usually obtained with S. carpocapsae against scarab larvae have been attributed to low powers of host search. However, a strain of S. carpocapsae selectively bred in the lab for improved host-finding of beetle grubs did not provide better control than the standard strain. This is probably because S. carpocapsae is poorly adapted to cause infection, and genetic improvement cannot be expected to overcome this.
Many species and strains of nematodes have been evaluated for control of Japanese beetle, with varying degrees of success. In one field study in New Jersey, two strains of H. bacteriophora and two strains of S. glaseri reduced grub populations to a level comparable with that achieved with the standard chemical insecticide (77%). In another field study two strains of S. glaseri reduced Japanese beetle grubs by 65%, while a third strain of S. glaseri, S. anomali, and a Steinernema sp. only reduced populations by 44%. Choosing an appropriate strain or species is an important factor in obtaining control of Japanese beetle.
Selvan, S., R. Gaugler, and J. F. Campbell. 1993. Efficacy of entomopathogenic nematode strains against Popillia japonica (Coleoptera: Scarabaeidae) larvae. J. Econ. Entomol. 86(2): 353-359.
Gaugler, R., I. Glazer, J. F. Campbell and N. Liran. 1994. Laboratory and field evaluation of an entomopathogenic nematode genetically selected for improved host-finding. J. Invert. pathol. 63(1): 68-73.
Selvan, S., P. S. Grewal, R. Gaugler and M. Tomalak. 1994. Evaluation of steinernematid nematodes against Popillia japonica (Coleoptera: Scarabaeidae) larvae: species, strains, and rinse after application. J. Econ. Entomol. 87(3): 605-609.
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