|SPRINGER T L|
Submitted to: American Forage and Grassland Council Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/12/1995
Publication Date: N/A
Interpretive Summary: Fungus gnats, Bradysia spp., are widely reported as pests of greenhouse grown ornamentals and seedling crops, but information is largely lacking about their effects upon economically important forage legume species. Twenty-one species were evaluated to determine which legume species were preferred and/or damaged by fungus gnats. The five most preferred species included: hairy vetch, Illinois bundleflower, cowpea, western indigo, and wollypod vetch, and the five least preferred species were: ball clover, kura clover, white clover, arrowleaf clover, and red clover. All species suffered feeding damage with 17 of 21 species averaging at least 70% seedling mortality. The "lack of persistence" of forge legumes is a problem throughout most of the USA as well as many other countries. In some areas, stand reductions of legume species may result from feeding fungus gnat larvae. Root wounding caused by feeding larvae not only weakens the seedling but also exposes it to secondary infections by pathogenic microorganisms. Several species of fungi are associated with the seed of legumes, thus the transmission of legume root pathogens may be accomplished by fungus gnats larvae and adults. At this time, economic losses caused by fungus gnats are unknown. Livestock producers that utilize legume components in their pasture base need to be aware of fungus gnats and their potential destructive nature.
Technical Abstract: Although fungus gnats, Bradysia spp., are considered common pests of greenhouse-grown ornamentals, field observations suggest that they may be pests of some forage crops as well. Twenty-one species were evaluated to determine adult fungus gnat oviposition preference and associated seedling mortality of 21 legume species in a replicated free-choice test conducted in the greenhouse in June 1992. Significant variation (P<0.05) in fungus gnat oviposition preference and seedling mortality was detected. The five most preferred species were hairy vetch, Illinois bundleflower, cowpea, western indigo, and woolypod vetch. The five least preferred species were ball clover, kura clover, white clover, arrowleaf clover, and red clover. A significant difference (P<0.05) due to plant-habit- type (cool- vs. warm-season species) was also observed in this study. Warm-season species were preferred nearly 2:1 over cool-season species. All species tested were susceptible to feeding damage with 17 of 21 species averaging >70% seedling mortality. Based on data collected in the greenhouse and the fact that fungus gnats have been reared from field collected sod samples of white clover, fungus gnats may post a threat to some forage legumes during seedling establishment.