Effect of mulches on persistence of entomopathogenic nematodes (Steinernema spp.) and infection of Strobilomyia neanthrana (Diptera: Anthomyiidae) in field trials

The effect of mulches on the persistence of entomopathogenic nematodes. Steinernema spp., for infecting larvae of the spruce cone maggot, Strobilomyia neanyhracina Michelsen, was tested in a series of field trials conducted in New Brunswick, Canada. Peat mulch increased the percentage of maggots infected with Steinernema feltiae strain 27 (=bibionis) (Filipjev) strain 27, S. feltiae Umea and Steinernema carpocapsae (Weiser) All strain, when maggots were placed on nematode-treated soil beneath the peat layer. However, when maggots were placed on the surface of the peat (to simulate larvae dropping) in a subsequent experiment, the percentage of maggots infected by S. feltiae strain 27 was less than half of that for maggots placed beneath the peat. Significantly fewer maggots were infected in peat than in either sand or potting soil in a laboratory experiment. Mean percentage of maggots infected by S. feltiae strain 27 over a 21-d period after application was not increased by retaining a natural vegetative cover, or by mulching with hay, wood-bark chips, or bark. Bark mulch, however, did reduce the rate of decline in percentage of infection over time. The numbers of S. feltiae infective juveniles present in the soil from 0 to 3 wk after application were estimated in 2 field trials by repeated baiting with greater wax moth larvae. Numbers of infective juveniles per gram of soil were positively related to percentage of cone maggots infected in 1 of 2 yr, but were not significantly affected by mulching. Mulching with hay, bark, or wood-bark resulted in significantly lower soil moisture potentials compared with nonmulched treatments. The results suggest that the mulches tested in this study would not maintain adequate efficacy or persistence of S. feltiae strain 27 for suppression of cone maggot over the 2- to 4-wk period of larval drop.