Fungus gnats are very serious pests in greenhouses, especially where propagation by cuttings takes place. We suspect that many disease problems in greenhouses are due to high fungus gnat populations. In 2003, several of the collaborators in the poinsettia nutrient monitoring project funded by the NYS IPM Program described fungus gnat populations that were not well managed, and they reported that root rot diseases subsequently developed causing serious losses. The larvae of the insects feed on fresh plant tissue and vector disease pathogens, such as Pythium, Fusarium, Verticillium and Thielaviopsis spp. Managing fungus gnats is not easy, since larvae may arrive in the bagged soil mix, can overwinter in the greenhouse floor, and adults can fly in from other sections of the operation or outdoors. Pesticides such as insect growth regulators will not affect the adults; some of the traditional materials labeled for fungus gnats are on the FQPA list for evaluation of chronic low dose effects. We prefer not to recommend materials such as chlorpyrifos and diazinon. The fungus gnat biological control products on the market include bacteria (Gnatrol, Bacillus thuringiensis), nematodes (ScanMask or Nemasys, Steinernema feltiae), and predacious mites (Hypoaspis miles). Although described in basic IPM resources such as the Guide for Greenhouse Florist Crops and Integrated Pest Management for Bedding Plants, relatively few experts recommend these products. However, they are widely used in organic greenhouses and appear to be cost-effective. In this project, we will examine several scouting methods for early detection of fungus gnat populations and test various biological control products for their ability to prevent outbreaks. If the test materials prove unsuccessful, intervention with a traditional insecticide may be necessary. There are several insect growth regulator products (including azadirachtin) that can be used without damaging the biocontrol organisms.