mosquito dunks for fungus gnats on seedlings?

erasmus_gwMarch 11, 2009

My flats of seedlings have fungus gnats which are stunting the growth of the plants. I read that the most non-toxic remedy is bacillus thuringiensis. I have some mosquito dunks which have that in them, but they dissolve slowly and I'm not sure what proportion to use. I doubt it would harm the plants to put too much BT on them but I want it to be strong enough to be effective and to work quickly. Do you think it would be a waste of time to try this? I have no idea what liquid BT would cost. Or maybe you have a different remedy for fungus gnats. They also have aphids and I haven't sprayed anything for that yet because I didn't want to do too many things at once to my seedlings. I potted them up a few days ago.


Thank you for reporting this comment. Undo

I put a 1/4 inch of perlite on top of the soil for my seedlings to help discourage the fungus gnats. So far, so good. Aphids? Plain water in a squirt bottle has worked while they are really small.


    Bookmark   March 11, 2009 at 11:52AM
Thank you for reporting this comment. Undo

what about spraying them hydrogen peroxide? i heard 3% doesn't hurt plant leaves and bugs don't like it. you could also go the way of good ole' soapy water.

    Bookmark   March 11, 2009 at 4:49PM
Thank you for reporting this comment. Undo

Thank you Connie and Ashes. Ashes, is insecticidal soap any different than plain soapy water? What kind of soap do you use? I think I'll try the perlite too and I guess I'll mix a mosquito dunk with some water and see if that helps.
Are you feeding your seedlings, Connie?

    Bookmark   March 11, 2009 at 5:10PM
Thank you for reporting this comment. Undo

I started feeding my seedlings when they got their second set of leaves, or thereabouts. They get a dilute solution of fish emulsion and seaweed each time I water.

Soap is okay on larger seedlings with good roots, especially if the aphids are particularly persistent. I don't use it on really small seedlings (I figure there's a reason that it's not labeled for use on cuttings, and I want to be cautious.) For these, a sharp spray from my squirt bottle can be enough.

My understanding is that fungus gnats are attracted to the damp organic material on the surface of pots. The layer of perlite is inorganic, and it prevents the gnats from getting to the soil. It also helps with damping off.


    Bookmark   March 12, 2009 at 6:57AM
Thank you for reporting this comment. Undo

Thanks, Connie. Some of the aphids are hanging out on the underside of the seedling's leaves...hard to spray off! I tried swishing the little plants upside down in water when I potted them up but I'm sure the aphids will be back.
Maybe the insecticidal soap will get them anyway...will just have to experiment with a few and see how they react.

I have an old jug of Neptune's Harvest which is I think fish emulsion and seaweed. I wonder if it is still fit to use. I'd think it would be full of bacteria from rotted fish..

    Bookmark   March 12, 2009 at 10:56AM
Thank you for reporting this comment. Undo
berrytea4me(Z5 CO)

Mosquito dunks work well for fungus gnats. I've used them on daylily seedlings. Any BT product will take several weeks to be effective though. I just put a dunk in my water bucket & let it sit for several hours or overnight before use. Leave it in the bucket for subsequent waterings.

There is a similar product that you can sprinkle onto the top of the pots called "Mosquito bits". The bt is released every time you water.

This year to prevent the gnats in the first place I poured boiling water through the potting soil and let it cool before planting. It was very effective. Not a single gnat all year.

    Bookmark   March 19, 2009 at 6:27PM
Thank you for reporting this comment. Undo

Thanks, Berrytea4me. Glad to hear someone else has tried it and it works. I ground some up and sprinkled it on the top of the soil but am still seeing gnats, so as you said, it must take awhile to work. Thanks for the boiling water tip.

    Bookmark   March 20, 2009 at 8:47AM
Thank you for reporting this comment. Undo

I'm thinking of adding mosquito ducks to my hydro system to control gnats. I see them buzzing around with the seedlings in coir pots. Is the BTI in these products living? If so, will they start a culture of the bacteria and keep on growing to help protect the plants? I looked up the patent number on the product (4,631,857) and the product has plaster as a binder. Plaster, I believe is calcium sulfate and slightly soluble. Will this cause problems with the nutrient solution and affect the chemistry?

    Bookmark   June 20, 2010 at 10:36PM
Thank you for reporting this comment. Undo

earlier today I was outside in my garden and had noticed gnats on top of my soil for my roses, so I came to both rose forums to see if anyone had posted a tip on how to get rid of them. then I saw this topic where hartwood mentioned using perlite on top of his soil, I decided to try this, and saw an immediate difference, bugs do not seem to like the perlite on top of my soil!

    Bookmark   June 25, 2010 at 6:10PM
Sign Up to comment
More Discussions
How does a Tea rose bloom on a Bourbon rosebush?
Could this have been caused only by having a Tea parent? or...
Need help eliminationg rose roots.
About fifteen years ago I planted a couple of rose...
cuttings for rooting
I have been a miniature rose lover for a long time...
Beth9116 zone 8a TX
Best way to start from cuttings
I used to be really good at starting roses, and it...
Chicago Peace Rose Help
Ok everyone I am looking for a Chicago peace rose for...
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™