I had a nursery fig tree arrive in the mail last fall which had just enough time to be potted get acclimated and go dormant. I didn't notice a gnats problem at that point, maybe a couple in the shipping bag. About late February I started to notice the fat egg layden females lethargically walking around that tree in the garage. At that point in time it was no biggy, they were isolated to the garage and squishing gnats gave me something to do. Yellow sticky traps caught many as well. I also tried the diluted H2O2, which helped also but didn't get rid of them. I gave BT a thought, but it seems the reports are that it helps but doesn't really wipe them out either.

By time the fig shuffle had arrived they had spread to all the pots in the garage but weren't much of a problem in the house for the cuttings and baby trees. When I put all my pots outside for good I thought nature would balance out the gnats well...naturally. Wrong! It turned into quite a gnat party out there, they were everywhere.

I decided to try predatory nematodes by Arbico Organics out of Tucson AZ, mostly because I don't want to have gnats even worse than last winter in the garage. I was hoping this will take care of them now and persist in my potting soil over the winter.  If I have large numbers coming out of every tree pot in the garage next winter...the upcoming cuttings would be screwed. I did my first treatment 2 weeks ago and the initial results are phenomenal. The nematodes prey on the larva in soil, not the adults. You mix them with water and apply, I used a watering can. You are then supposed to keep the soil moist for the first several days. You are also supposed to retreat in two weeks to address any later cycles.

Here's my timeline after the 1st treatment.

2 days- No noticeable affect
4 days- Maybe some lessening, not quite sure.
7 days- Defintely some noticeable change, maybe 40-50% reduction
10 days- We are on to something, 70-80% reduction
12 days- 90% reduction  :)
14 days- 2 gnats found total after looking for them in every pot. Safe to say 98% reduction. Second treatment applied.

They keep for a month in the fridge. It took a couple weeks to recieve my shipment. I think this would be a viable option for those who had high cutting mortality rates due to fungus gnats. The last cutting I started this spring came from a last minute pruning before putting my trees out in the fig shuffle. This luckily was the only cutting which was affected by fungus gnats and confirmed larva in the cup(it was at the 2 leaf stage with some roots) and got treated along with all the other potted plants. I don't see any gnats on that plant any more, it has recently been potted and is doing fine.

Calvin,

Thanks for the info! That's awesome !
I am curious, since the nematodes attack the larvae inside the soil in the pot, how did you measure the reduction %?
Did you look inside from time to time?
I assume, whatever gnats are flying, is not an indicator of the reduction.

My reduction rates are simply based on the amount of adult gnats observed in the vicinity of the trees before and during/after treatment. I have no way of measuring larva other than their adult form. They really like to hang out on the potting soil surface, the clay pot and all its margins, as well as on the tree to a lesser extent. Flying around seems to be pretty minimal. Is it possible there is some other influence?..always. The last cutting with larva in the cup was inside until a couple of days ago though, and gnat activity ended there after 10 days as well.

As it stands, I am a believer. For me the next step will be to see what happens throughout the remainder of the year and the upcoming winter and spring. I'll update this post accordingly.

Calvin, Do you have a link to buy these by chance?

Found it and think it is going to be a must have for winter indoor growing.
http://www.arbico-organics.com/product/nemattack-nematodes-feltiae/266

Thanks for bumping this. I ordered some since most of my plants are indoors for the winter. These stoopid gnats make me crazy!

My last bag of potting soil was bad and I have been in the process of repotting most of my little things. I hope this stuff works.

This is great!  They say that they work on leaf miners too.  Those keep getting into my tomato and brugmansia plants!  Inside and out I think this is going to really help.  Thank you!

I use a similiar product called actinovate on my tomatoes for blight, and this year I sprayed my figs twice as well, once before leafing out and once mid summer.  I believe that is under-dosing, but it nevertheless seemed to delay the onset of the ever-present early-fall rust here in south LA.  I had not considered using it on my cuttings, but I will give it a go.

The stuff aint cheap, but it goes a loooong way.  I am considering applying on my lawn as well, as it has some activity on brown patch, another ubiquitous fungal issue here in the moist south.

I bookmarked that link!  Thanks!  My new issues are with gophers and critters that eat fruit, but those gnats have destroyed many of my cuttings in the past.  The only drawback is I'd need the Small Ranch Size!  YIKES! 

Suzi

I wanted to bump this again and report that it does work, thank God! I got my stuff and kept it in the fridge until about 2 weeks ago when I started to get everything ready for the trip inside. It was very easy to use. I watered everything with the nematodes and kept the pots moist. No gnats! This is something that I will definitely be using every year.

Here is an end of season update. All in all, I used it about four times on my containers and around the yard, I figured use it if you got it because you can't save it for too long. I found that from time to time there would be a sudden influx of gnats around one of the treated containers, but only for a week or two, which I imagine was the amount of time it takes for the predator/prey curve to reassert itself. I need to figure out what to do for the newer plants I started in the later part of this summer, as this untreated soil will be fair game for the establishment of a new gnatopia. I still have some PN left but it looks pretty dried up and I doubt they are still viable, I'm going to use it anyway.

I now place all moss before using it for rooting and bags of orchid mix I use for potting up cuttings into the microwave for 10 mins. Add a little water is you wish to create steam and also some soil fungus will not survive also.  The issue I saw was many bags of long fiber moss are not well sealed or have eggs already sealed in. Hand harvested stuff also has a feast of critters that wake up when brought inside.  Best to coordinate this event with spouse or do when they are not home, "curing" potting mixes in the kitchen is not favored by some....Flea market microwave in the garage works well!

A timely note, Jack!
I was thinking to do the same. The mix stinks like hell and the smell stays around for long (those who brew beer at home could compare this to the brewing beer smell. Basically, only one can survive, either beer or your spouse :)

thanks for the link. Now to start a battle against scales which is eating away all mu leaves.

I nuke my starter soil mix, I think it is a great idea. I don't bother with the sphagnum though I do initially soak it in hot water, I have never seen a gnat in my rooting bags.

I am a big fan of the nematodes, I used them to get rid of a gnat infestation in my worm farm a few years ago and after I lost a bunch of cuttings I have been adding them to all my pots and seem to have gotten rid of them again... I should write a children's story... My Friend the Nematodes.