The occasional failure of entomopathogenic nematodes to control pests may be attributed to poor strain selection or incompatibility with the habitat, particularly available moisture. But little is known about just what soil and moisture conditions will optimize nematode survival, particularly in potted woody ornamental production where nematodes can be used for black vine weevil control.
Experiments in New York greenhouses using the cold-tolerant nematode Heterorhabditis bacteriophora 'Oswego' examined nematode survival in several types of commonly-used greenhouse potting soil mixes.
Watering from the top down, a typical greenhouse and nursery production method, tends to flush the nematodes out of the soil altogether. Nematodes were no longer detectable in all soil types within 30 days of overhead watering. When the watering regime was changed to sub-irrigation where pots are placed in water-holding trays nematodes persisted for at least 120 days.
Choosing the right soil mix is critical, too, for improving nematode survival, since population levels of nematodes varied among the soil types tested. However, the experiments are still continuing, so no recommendations can be made yet on the best soil mix to use to enhance nematode survival and efficacy in potted plant production.
Cowles, M. H. and J. P. Tette. 1999. Biological control with nematodes: Increasing the odds of success. New York State Integrated Pest Management Program 1999 Annual Report, page 27.
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