Greenhouse flies

Discussion in 'Garden Pest Management and Identification' started by soccerdad, Apr 13, 2008.

  1. soccerdad

    soccerdad Active Member 10 Years

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    Vancouver, BC, Dunbar area
    I start seeds indoors. This year most of my flower seeds have not germinated, and the few that do germinate have tended to grow about 1" or so and then the leaves start to brown at the edges and eventually die, and then the entire plant is dead.

    I have lost all my salvia, all my nemesia, all my silene ...

    My peppers, which are about 8" tall, have had their uppermost leaves turn all crinkled and small, the lower leaves have turned yellow.

    The source of the problem appears to be small flying insects which originated who knows where.

    The insects look like tiny mosquitoes - about 1/8" long - when caught on yellow sticky paper. They do not look anything like whiteflies. They do not sting, and there is in any event no place nearby where mosquitoes would breed. They are not attracted in the slightest to the paper. They do not appear to be harmed by insecticial soap.

    They are far too small for me to post any pictures, but does this description ring any bells with anyone?
    Last edited: Apr 13, 2008
  2. plantenthusiast

    plantenthusiast Active Member

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    Vancouver Island, Canada

    Do they look a little like fruit flies? If so they may be soil gnats (otherwise known as fungus gnats), which are notorious in pots indoors and greenhouses as well. They are a real pain.

    They lay their eggs in moist soils, and when there are large numbers, the larvae may feed on the tender roots of plants.

    Over watering or too frequent of watering often encourages fungus gnats. Try to let the soil dry as much as possible (without doing damage to the seedlings) before watering again. I keep my seed trays sealed in a clear polyethylene bag until I see signs of germination. That will help keep them out for awhile.

    Various insecticides work, but I don't know that you'd want to use them on tender seedlings; have you tried Safer's Soap? My aunt swears that if you spray the soil as well, that it will help to control the gnat larvae. I believe that there are organic insecticides based on Bacillus thuringiensis that are effective in controlling gnats; you'd have to check around. Apparently yellow sticky cards or tape near the soil will help as well. There are various biological controls and predatory insects that you can use, but those may be harder to come by, not to mention that you wouldn't want more bugs in your house!

    Also you may consider watering from the base via a tray; as I understand, the larvae tend to reside within the top inch of the soil. Do not put too much water in the tray though, as this will oversaturate the entire pot/tray and not solve anything.

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