Golden Pothos has fungus gnats

amav31August 27, 2013

I have had this plant for 12 years and never had gnat problem.
The plant become really big so I changed it into a bigger pot and I used Vigoro plant mix from Home depot.
Since then I have had these fungus gnat problem. I tried cinnamon and hydrogen peroxide and vinegar sprays. Not much effect. Today I sprayed neem oil mixed with water. Looks like it may work. But too early to tell.
My questions is , once I bring this gnat under control hopefully with neem oil, should I change the potting mix? Will the gnats lay dormant and come back again.? Should I change only the first 2 inches of the soil or the entire soil in the pot.
I have caught the adult gnats by using apple cider vinegar and the fly catcher bat.

Any tips to prevent this in the future, is much appreciated.
I do not over water my plants BTW. Did anybody try neem oil and vouch for its effectiveness. I am trying to go chemical free to treat these gnats.

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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

Ugh, sounds like they were in that soil you bought. If there's any left, let it dry out completely. That should get rid of them in the unused portion. I don't pay much attention to discussions about products like neem oil because I don't have anything like that, but don't remember hearing about using it for FG's. There are many discussions about FG's here, I might suggest this one.

Since the plant in question is Pothos, I would probably just snip everything off at the soil level, let the soil dry so the FG's all die, then put the stems back in when soil's ready and the stems have begun to make new roots - the aerial root nubs turn white, get longer. Not sure how effective this would be if they are in other pots by now...

    Bookmark   August 28, 2013 at 9:58AM
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rhizo_1 (North AL) zone 7

Vigoro is one of the worst potting media you can buy. I strongly urge you to get rid of it completely. That is one of the primary contributing factors to any fungus gnat infestation. Mucky sedge peat is the culprit.

If you use the search function for 'fungus gnats ' in this forum, you'll come up with helpful suggestions. Neem won't be on that list, or cinnamon, peroxide, nor vinegar.

Changing your potting mix to a very coarse textured medium is a good first step. Allowing it to dry out appropriately between waterings is another. Should you still have problems after that, the next step is Bt-I (Bacillus thuringiensis Israelensis) .

    Bookmark   August 28, 2013 at 2:17PM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

That's what the link on the word "here" is above, a search for "fungus gnats" in this forum. The one I suggested was recent, and had advice from you, Rhizo, near the top.

Another vote for getting rid of peat, had no idea what Vigoro was. Since I've gotten rid of peat, even before catching on to the 'more chunky soil' thing, so many fewer plants have died, and now it's extremely rare at all with the chunky soil. Stocking back up over the past few years on so many that I'd killed before and finally they look great although I still can't stop adding more water to plants that don't really need it yet, at least while they're outside for summer and it's so easy and fun to do. Fungus gnats are extremely unlikely to find this type of soil a suitable environment for breeding. Not had issues with those since changing either.

    Bookmark   August 28, 2013 at 2:55PM
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tommyr_gw

Get a package of "Mosquito Dunks" and put a quarter of one in your watering can. This will kill the soil larvae. Use sticky traps for the adults flying around.

Tom

    Bookmark   August 28, 2013 at 7:29PM
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amav31

Thanks for all the advice and useful links.
It is best to stay away from Vigoro and Miracle gro special potting mixes. Is there any specific potting mix you guys recommend. Do stores even carry 'ordinary' potting soil.
Should I add perlite in soil, to make it more airy ?

    Bookmark   August 29, 2013 at 8:10AM
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Tiffany, purpleinopp GardenWeb, Z8b Opp, AL(8B AL)

A wide variety of options and methods are available, including specific recipes, but the basic principle of having something more chunky (not tiny particles) that dries much more quickly is the heart of the matter. It's not so much about the brand name, just that the same stuff is in most bagged potting soils. The biggest offender seems to be peat, followed closely by anything that is/has small particles, like genuine dirt from the ground, sand. I think this info is a great place to start.

(Also, when you repot after switching, there's never a "root-filled sponge" that's impossible to separate, roots from 'soil.')

Does that help?

    Bookmark   August 29, 2013 at 10:03AM
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amav31

Thanks purpleinopp.! That was a informative article.
I googled for some basic recipes for homemade potting soil and all of them use peat moss. I checked out youtube too.
Do you have a simple recipe that has chunky particles in the soil and avoids peat?
Thanks.

    Bookmark   August 29, 2013 at 1:47PM
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asleep_in_the_garden

The very basics of Al's gritty mix are:

1 part Bark Fines
1 part Turface
1 part Granite

Fine tuning on all that can be found all over GW...LOADS of info! :)

    Bookmark   August 29, 2013 at 2:14PM
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amav31

Thanks asleep_in_the_garden.

    Bookmark   August 31, 2013 at 9:54PM
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