Shore flies and moth flies in the greenhouse
Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Some greenhouses are seeing lots of shore flies and moth flies now. Although they don't cause plant injury they can be a nuisance. The larvae of both species proliferate in very wet soil. In previous tests where we monitored weekly trap catches of shore flies in greenhouse growing plugs we saw a big outbreak of shore flies towards the end of the root development period when the plugs still had to be kept moist all the time.
As soon as the growers were able to let the soil dry between waterings, the number of shore flies began to drop rapidly. I expect to see the same thing with moth flies. Meanwhile, to help you live with this problem until the numbers go down, I suggest trying Adept as a soil drench or Astro, Attain, Decathlon, Mavrik, Scimitar, Talstar or Tame as a foliar and soil surface spray.