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Posted:  13 Feb 2012 21:42  
Hi, my name is Vicki with InnerGreen Plant Service. My husband and I have a small interior plant business. I was wondering what other companies are doing with gnat problems. It seems that every bag of soil we buy, to do transplanting,etc... has gnats! It's so frustrating and has almost cost us some accounts. We do use the yellow sticky strips but was wondering if there was any other solutions. We use top quality Miracle gro potting soil and still get gnats. Would appriciate any feed back. Thank you
Posted:  14 Feb 2012 02:39  
I hate to tell you this, but we stopped using MiracleGro soil for that reason.

Use a professional, baled, compressed soilless medium like Sungro's Sunshine Mixes (#2 or #4 for extra perlite).  They come very dry and devoid of gnat larvae.  After that, it's up to you to keep 'em clean by not introducing gnats to your accounts in your plants.  Pre-treat with beneficial nematodes prior to installing or replacing plants and you'll be golden.

Posted:  14 Feb 2012 23:40  
I used Special Blend (very similar to sunshine mix #4) on an installation job and Pro-Mix BX on another.  I have a few fungus gnats in a pot with a Ficus alii in it, but not many.  That was with the Pro-Mix BX.  They probably came along with the soil in the grow pot, as well as some millepedes, which may also be helping to control the fungus gnats.  And in the planters with Special Blend, it's not an issue at all.

I find the yellow sticky strips are not a remedy, just a monitoring device.  I've had good luck with Pyrethrin, as well as Schultz brand Fungus Gnat Spray (contains Resmethrin and Tetramethrin.)

I have had an issue with them at home and I alternate between these two chemicals; I find they've worked.  I used to swat them away while sitting at my computer or watching t.v., or eating supper, but not anymore.  I tell you, it's luxury to be rid of them!
Posted:  15 Feb 2012 19:06  
Welcome! And, OH NO! I love Miracle Gro products! I did notice a gnat problem with the Organic Choice Potting Mix, but haven't experience it yet with their Moisture Control Potting Mix. Now, I'm nervous! Also, I agree with number2211 about the sticky traps. They're not meant to be a solution to the problem, just for monitoring them.
Posted:  16 Feb 2012 01:58   Last Edited By: Clem 
It's probably okay if your source keeps the potting mixes indoors for dry storage, but if they're on pallets out in the elements, you WILL get fungus gnats in every plant you use it on.  MG mixes contain a lot of tasty gnat chow:

"Our potting soils generally contain peat moss (the major component that is harvested from natural peat bogs), compost (the compost may contain animal manures, composted leaves, grass clippings, and/or composted bark), and perlite (white volcanic rocks used for drainage and soil texture). Some contain Osmocote fertilizer that look like small clear fluid-filled balls."

"The Miracle-Gro Moisture Control Potting Mix also contains composted hulls of coconuts to help absord more water than regular potting soil. This is the Aqua Coir (pronounced "core") component of the soil." (http://www.scotts.com/smg/catalog/productTemplate.jsp?proId=prod70262&itemId=cat50154&tabs=help)  Coir is good stuff and not commonly associated with gnats, but it's mixed with compost, which is a veritable witches' brew of gnat fodder. 


Posted:  02 Mar 2012 00:02  
Thank you all for you're input. I love this website!!!!!
Posted:  02 Mar 2012 01:51  
Come back anytime, Vicki.  So which potting mix have you switched to?

Posted:  02 Mar 2012 06:22  
Try nematodes that you water in.  And try a small amt. of sand on top of the soil. Hope you get the gnats under control!
Posted:  05 Mar 2012 00:56  
1. Sticky traps for individual plants 

2. Nematode treatments, as many as necessary

3. If all else fails, pull everything and replace!  Customers will cancel in a heartbeat if they're constantly swatting gnats!
Posted:  05 Mar 2012 02:11  
Sticky traps (more accurately known as "monitoring cards", because that's what they're designed to do...help you monitor insect pops in greenhouses, etc.) are NOT a control method.  They will let you know where the highest concentrations of gnats are located, and possible exclude individual plants or areas from suspicion of harboring gnats, but they do very little to reduce pest pops...if you catch ten gnats from an infested plant's soil, chances are thirty more got out unscathed to breed a new generation, unless you carpeted the soil of every infested plant in the account with sticky traps!

Nematodes are a good long-term control method, breaking the life cycle of the gnats and giving some residual presence in the soil in case surviving reproductives return to lay more eggs there.  They will NOT give quick knockdown, however...it will take two weeks or so to control all the larvae present in infested plants' soil if applied properly.

A drench of Marathon II will quickly kill gnat larvae present in the soil.  You can then introduce nematodes on a repeat basis to maintain long-term control.  But the best strategy is to pre-treat any replacements or new plants before installing them, because otherwise you can just re-introduce the pest yourself.


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