Help! Host seedlings and fungus gnats advice needed fast!

17 years ago

I potted my hosta seedlings that I started on papertowels about two weeks ago. I baked my potting mix in the oven before I started also. Even so, I saw a couple of gnats flying above them when I checked on them today. Is there anything I can treat the soil with without killing my tender seedlings? These are only mutt seeds that I collected from my plants last fall, but I have some started on papertowels now that I paid good money for. I am wondering if there is anything I can do besides baking the soil to prevent this when I plant these. P.S. I have my seedlings in my greenhouse if it makes any difference. Thanks, Raye

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raye
Original Author

17 years ago

Well if you don't think they will be a problem I won't worry so much. I thought I heard or read somewhere tho that the larva would eat the roots of tender hosta seedlings.

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Comments (13)

raye
Original Author
17 years ago
Hey I got to thinking after I made the post, what about Murphy's oil soap? Could I water them with some weak Murphys oil soap water? Anybody have any idea of the ratio of soap to water I should use if it would work? Thanks again, Raye
greenguy
17 years ago
i have been dusting the top of my soil with bone meal when i plant and it really seem to help as i haven't had any issues this year. Saying that i do not think it will rid you of your problem. I am not sure the best way to be rid of the little buggers but i know what a pain in the @ss they can be do good luck.
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Sounds like you have a few good suggestions, Blossomgirl. One option that I haven't heard floating around is to simply repot. No chemicals needed. The larvae live in the medium. No medium, no larvae. You can also use a horticultural oil or insecticidal soap as a drench, and that should kill larvae and adults in the medium alike. The key is also to run your plants drier so you kill off the larvae that thrive in moist environments. I would also like to correct a couple misconceptions I have read in this thread: 1) the larvae do NOT eat orchid roots or algae. They eat the fungus in the soil, nothing more. hence their name Fungus gnats. Proper treatments for commercial production always include a fungicide. 2) the presence of gnats does NOT necessarily indicate that the medium is too wet. Gnats are resilient little buggers and survive on less moisture than you think. I've had plants stay bone dry for a couple weeks, only to water and have them still be there. They can be pretty difficult to get rid of. The "too wet" mantra is a bit outdated, especially when you consider there are a lot of plants , like spathiphyllums and caladiums, whose preferred moisture level is definitely on par with ecology of gnat larvae. It makes sense if you have gnats on a cactus or other dry-thriving plants, but not with the majority of other plants we have in our collection
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See the other current discussion here. Id that doesn't answer all your questions the search will pull up many more discussions about them. Dave Here is a link that might be useful: Fungus gnats
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The only thing I know of that will take care of them in seed pots/containers is BTi - Bacillus thuringiensis subspecies israelenis, the subspecies is important, the kind for caterpillars doesn't work. BTi kills the larvae and stops the breeding cycle, safe for pets, birds, us, it's only lethal to gnat and mosquito larvae. Available Knock Out Gnats, Gnatrol, others, or in a pinch make your own solution with Mosquito Dunks (and pass the rest of the package on to someone with a water feature or pond in their garden). Float a dunk in a container of water overnight, and use that to water your seedlings as they need water - at least three consecutive times on your regular watering schedule. You can wet, let dry, wet dunk again and use over....doesn't alternative the effectiveness of the dunk.
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Hey Jinny...I don't blame you for not using peat in your mixes..I refuse to use it in many too, especially all my plants I like in the gritty..I didn't realize you said that you use the gritty mix only now, my bad...Good for you)) I think asked if it was bad to use the 'mix', 'Natures Care' with feather meal and stuff...I just wanted to encourage you to use pure 'peat' since any other additives could cause a gnat issue if you were to make a 5.1.1 again...Keep up the good job with the gritty !! If anything, everyone should use the gritty since it does not weigh as much as they think it does when wet....Believe it or not, sometimes I will make the 5.1.1 without peat substituting 'pumice' or 'surface' instead and it is awesome!!! All my Hoya thrive in this and many of my citrus.... Jersey, I bring both the gritty and 5.1.1 mix plants into the house..It must be me, but I have pots full of the gritty and the 5.1.1 and they both seem to weigh the same to me...I don't make a mix ahead of time and store it for more than a week or so...I am afraid it will decompose too much by the time I use it. I will actually soak my bark for a few days but without the peat..Then I use that damp bark and mix it with the peat and perlite as needed to keep it as fresh as possible.... I love how your tree looks in that pot and the color of that mix..Good job..By the way, I had no idea all of us had FIGS in common.. I think we are all too much alike in the plants department! I just finished picking 20 ripe Black Mission, as sweet as they could be...What kills me, is that some can have a problem in one area and some of us nothing in another..I never saw a bee go for mines...Crazy and over 27 varieties...
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jspece
17 years ago
BTi (Bacillus thuringiensis israelensis). I just learned about it about 2 months ago and started using it on my Hosta seedlings I have under lights. At the time then gnat population was getting to be annoying, but as of today it is almost a non-issue. I still see an occasional gnat as I water so it may not be 100% eradication, but nearly so.

BTi is the same strain of BT that is used to control mosquitoes. I just keep a small chunk of "mosquito donut" in my water tank. Replace it about every other time I fill the tank (amounts to about every 7-10 days). There is also a granulated form that you can mix right into your potting mix at planting time.

Easy and safe!!
maryann_____chgo
17 years ago
I haven't had gnats for a couple years since I started sterilizing my soil by pouring boiling water thru it, but a some quick fixes are to smear vaseline on a Joy detergent bottle, (gnats are attracted to yellow and get stuck in the vaseline); otherwise spray them with flying insecticide.

Are you bottom watering? This discourages the moisture loving gnats and draws roots down.
ken_adrian Adrian MI cold Z5
17 years ago
you sterilized your soil ...

did you sterilize the greenhouse ....????

it would be like saying i autoclaved [heat treating for surgical gear] the scalpel .... and then did surgery in the alley ...

if you properly cooked the soil .... then they were NOT coming from the soil .. but they might be in the soil now ...

good luck

ken
ken_adrian Adrian MI cold Z5
17 years ago
BTW ... the gnats have little or no impact on the hosta as far as i know... the biggest problem is them flying all over the house when you do this indoors... it can be maddening to try to watch TV with a horde of them flying around it.. lol ..

since you are working in a greenhouse... it might not be all that big a deal ... i do NOT know how to rid a greenhouse of them .... probably a bug bomb will work ...
highjack
17 years ago
You are correct Raye, they will eat the tender roots. I think Ken means the adult flying pests do no harm EXCEPT they reenter the medium, lay eggs, eggs hatch into larvae, they eat the roots then they crawl out as adults and begin the cycle again.

Josh is correct with the BTi remedy. Safe to use for humans and your seedlings, death to the larvae. The yellow sticky solution will capture some adults to kill them before they reenter the medium. Grit or sand on top of the medium will discourage the adults from reentering the medium but then you have to water from the bottom to keep the grit in place and dry.

If you brought any other plant into the greenhouse this was probably the start of your problem, not the sterilized mix. Treat ALL plants with the BTi or you will never get rid of the problem. I discovered this year that sphagnum moss also carries the eggs of the pest - not good when you grow some of your orchids in pure sphag.
greenguy
17 years ago
"Grit or sand on top of the medium will discourage the adults from reentering the medium"
probably why the bone meal has helped me
raye
Original Author
17 years ago
Where can you find the BTi stuff??
ademink
17 years ago
Lowe's, Home Depot, etc...look for Mosquito Dunks
jspece
17 years ago
They will be in the water garden section. Mosquito Dunks or Mosquito Bits are two brand names I'm familiar with. Most garden centers and big box stores will have them.
redclaygirl_1954
14 years ago
If I treat my new incoming plugs wtih BTi right away, will that help keep them from invading my newbies or do I need to remove the infested crop outdoors?

Help! Host seedlings and fungus gnats advice needed fast!

raye
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raye
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Help! Host seedlings and fungus gnats advice needed fast!

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