Fungus gnats are more than a nuisance pest One of the interesting aspects of this year's 23rd Annual Society of American Florists Pest and Disease Management for Ornamentals Conference was the increased focus on using alternative controls for insect and disease pests. There was still plenty of discussion about chemicals, but I got the sense that there seems to be more interest on which alternative controls can be used with "traditional" chemical controls. It was quite clear that if you aren't scouting regularly and using sticky cards then it doesn't matter what control you use -- they're effectiveness is going to be limited. It was repeated throughout the conference that a preventive program is the best way to stay ahead of what might ail your crop. Insect/disease interaction Control of fungus gnats may be even more critical based on research by University of California plant pathologist Mike Stanghellini. Previously, the adult stages of these insects were considered to be primarily a nuisance. Studies by Stanghellini have shown that both the adult and immature stages of these insects can transmit disease pathogens such as Verticillium, Fusarium, Phytophthora and Thielaviopsis. Adults carry spores on their bodies and the larvae are capable of ingesting the fungi and excreting viable spores. Scott Ludwig, entomologist with Texas Cooperative Extension, reported that severe infestations of adult fungus gnats and moth flies on Texas container roses have caused retailers to reject plants. The flies usually don't emerge until the trucks are opened and plants are unloaded at retailers. Think prevention Monitoring with yellow sticky cards weekly is the best way to keep a check on fungus gnat adults, Ludwig said. For the immature stages, place potato disks in the growing medium. One of the best (and cheapest) ways to reduce fungus gnat outbreaks is to limit watering under cool, wet conditions to hold down algae growth, Ludwig said. Remove and discard any plant debris, old growing media and diseased plants. Some "natural" fungus gnat controls are being studied. At low fungus gnat and shore fly populations, apply multiple applications of Steinernema spp. to control the larval stages. Another natural control is the Old World hunter fly, Coenosia attenuate. This small predatory fly won't provide 100-percent fungus gnat control, but is capable of suppressing both larvae and adults. Ludwig said once the hunter fly is established in the greenhouse, it's not difficult to maintain. To learn more about insect and disease strategies from this year's SAF Pest Management Conference, the proceedings are available for $44.95 to members and $64.95 to nonmembers. SAF, (800) 336-4743; www.safnow.org. Send this article to a friend Enter your e-mail address: Enter your friend's e-mail address: Click the image below to send: © 2007 Branch-Smith Publishing