Beneficial Nems for Fungus Gnats

Indoor organic grow and a basic organic IPM which has worked well over the past several years however I have recently experienced a significant fungus gnat invasion which I have chalked up to using a horse manure-based compost top dress over my usual use of EWC. This along with my standard practice of maintaining consistent moisture under my mulch layer resulted in a significant outbreak.
I am on week 5 of flower so I looked at other options instead of neem oil. I first removed the mulch layer and the first couple of inches of soil from my 10-gallon fabrics. Set up fans across the pots and allowed the first couple of inches of medium to dry. I then powder applied DE across all pots soil surfaces and placed sticky traps in all containers. At first this approach knocked down the hatched gnats significantly. I then replaced my top dress with a EWC based blend and applied a new mulch layer. And then they came back with a vengeance as the recently pupating larva hatched over a week later.
At week 2 of this challenge, I decided to bring in some warriors through the addition of beneficial nematodes. I applied Steinernema feltia at a rate of 3,000,000 active nematodes per 50 gallons of soil 4 days ago but continue to identify a medium level of hatched gnats on the sticky traps.
If anyone could share insight on these issues as perhaps, I am expecting quicker or more positive results going into day 5. Should I consider applying another round of nems after 7 days or is the pupating stage longer than the 4-5 days?
At this stage, my flowering crop is not showing any significant signs, but I want to take these bastards out before they do. Any suggestions would be appreciated.

diatomacous earth over the soil works well against gnats too

Will the DE affect the application of nems?

I'll just watch. I hope the beneficial nematodes are friendly to the micro beasties in my living soil. Good luck...

good question, you would have to do the nematodes first and then aply the diatamacias earth after

Fungus gnats are the only bug issue I’ve had in my year of maintaining almost 200 plants at any given time. Tried various neem and thyme sprays, and even grandevo and venerate, none of which seemed to do much. Even added a top layer of perlite; no help. Went the beneficials route with sf nematodes, rove beetles, and hypoaspis miles (these should already be in your ewc). Went from a pretty serious problem to not seeing any gnats within about 3-4 days. I wouldn’t have believed this if I didn’t experience it myself. I’ve noticed they’re starting to come back after about a month as I introduce soil that wasn’t treated. Sticky traps help a lot.

Good to know. Perhaps I will continue monitoring with sticky traps and hit them with another round of the nems in 5 days.

Northern Boxer said:

Good to know. Perhaps I will continue monitoring with sticky traps and hit them with another round of the nems in 5 days.

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I use the mosquito dunks in my reservoir. This like nematodes takes a few weeks to really make an impact. Also after recycled soils are used a few rounds they typically just go away.

I had them pop up in my last grow, all I did was mix up the usual 5 ml neem per liter of water and 2 ml silica. Sprayed the top of my soil in all my pots AND the sides of the fabric pots. All gnats gone after a week of treatment, sprayed once per day. I'm planning on getting one of those beneficial insect packages once my 4x4 living soil bed gets set up, as long as I can get them before the temps outside kill everything in the mail. I'm curious if these nematodes will actually correct an active fungus gnat invasion?

I will provide an update once I have at least 10 days of treatment under way.

Next time you can just put about 2" of playsand over everything.This kills them instantly and the adults cant get in too lay eggs.You have water slowly so not to disturb the sand but it works and sand is cheap.