Application rate and timing, potting medium, and host plant effects on the efficacy of Steinernema feltiae against the fungus gnat, Bradysia coprophila, in floriculture

Abstract

Abstract Effects of three nematode concentrations, five application timings, four potting media, and two host plants on the efficacy of Steinernema feltiae against the fungus gnat, Bradysia coprophila, were studied in the greenhouse and growth chamber experiments. In New Guinea impatiens (Impatiens hawkeri), application rates of 1.25 and 2.5 × 105 infective juveniles/m2 of S. feltiae equally and significantly reduced the population of fungus gnats relative to the control but in poinsettia (Euphorbia pulcherrima), 2.5 and 5 × 105 infective juveniles/m2 produced similar reductions. Nematode efficacy against the fungus gnats was significantly lower in the nursery-mix as compared with Ball-mix, Metro-mix, and Pro-mix potting media. Nursery-mix was also favorable to fungus gnat colonization and had the highest infestation. Application of S. feltiae to the Metro-mix and Pro-mix significantly reduced B. coprophila emergence relative to the control 7 days after treatment but in the Ball-mix it took 14 days. In all the four media, poinsettia supported significantly higher numbers of fungus gnats than the impatiens but nematode efficacy was higher in the impatiens. Application timing affected the efficacy of S. feltiae against fungus gnats infesting poinsettia but not impatiens. In the growth chamber, only application 16 days post-transplanting significantly suppressed the fungus gnat emergence as early as 31 days after treatment and remained significant throughout the experiment but all other application timings (0–8 days post-transplanting) suppressed the fungus gnat emergence only after 75 days. In the greenhouse, all four application timings significantly suppressed the fungus gnats on poinsettia relative to the control 34 days after treatment. We conclude that nematode application rate and timing, potting medium, and host plant are all important factors in the control of fungus gnats with entomopathogenic nematodes.