Fungus Gnat and Shore Fly Adults can be seen around moist growing media, especially media with algae growing on its surface. Both can be a nuisance and help spread diseases. Fungus gnats tend to fly in a zigzag pattern close to the media surface. Shore flies are often seen resting on plant leaves. See photos.

Fungas Gnat Adult
Leanne Pundt photo.  Click for larger image

Shorefly Adults
Leanne Pundt photo.  Click for larger image

Unfortunately, many growers mention how difficult it is to control adult shore flies or fungus gnats. Some growers are trying low rates of insecticidal soap (M-Pede, Insecticidal Soap) and spraying when adults are settled and you are more likely to contact them. Mass trapping of the adults with yellow sticky tape or large yellow cards may also help. Moving the plants outside (depending upon the crop tolerance for cool night temperatures) will increase the air circulation around the plants, drying out the media and helping to discourage both of these pests.  

The long-term solution is to discourage algae growth – avoid over watering, provide proper ventilation, use disinfectants to keep your irrigation system free of biofilms by using hydrogen dioxide (XeroTol or Oxidate) during crop production or Spectricide in between crop production.  

Shore fly larvae only feed on algae, but fungus gnat larvae can feed upon and damage young tender roots. If you are seeing large numbers of adult fungus gnats, inspect root systems for fungus gnat larvae and their damage. Many growers report that insect growth regulators (Distance, Citation, Ornazin) have been working well against the larvae. The neonictotindoids (Safari, Flagship, Marathon) have also been working well this spring.

Downy Mildew on Coleus – is a relatively new disease that has started to affect some growers in 2005 and 2006. Symptoms may include leaf spotting, twisting and leaf drop. Because of the relatively sunny, dry weather conditions this spring, when I have seen infected plants, I haven’t been able to see very much, if any, of the typical “fuzzy” fungal sporulation that one often sees on the underside of the leaves that are infected with downy mildews. Both seed and vegetatively grown coleus are susceptible.  

For more information on this disease, see the update and photographs from Margery Daughtrey, Senior Extension Associate, Long Island Horticultural Research and Extension Center at the Cornell Greenhouse Horticulture Web site - http://www.hort.cornell.edu/greenhouse/

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