Predatory Nems for Fungus Gnats

Northern Boxer

420 Member
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.
 
I use mosquito dunks to treat my plants water- 2 or 3 waterings with the dunk treated water, and soil gnats will be just an unpleasant memory...
Search mosquito dunks on the forum- lots of info will come up- they work very well to rid your grow if those little bastards once and for all.
 
Hi Northern Boxer, That's a drag. F gnats have maggot young and they don't do well with Bacillus thuringiensis, that's in Safers Garden Dust. If I remember right they have a lifecycle of 10 days and if you inoculate the soil with it, they decrease in a big way.

I also put a fan directly on the soil as they are poor flyers and will be trapped in the pots where I lay a yellow sticky trap on top. Your microbes will be safe and the grow will get better within ten days, and improve along the way. I may apply it again in a month if they're still heavy. It's happened to me exactly the way it did to you with manure.

They talk about vinegar traps but I have had no attraction to them at all. In my finished journal link there's a Martian Darkness journal where I had them for the same reason you do, and fought and won.

It's the same ingrediant as Carcass's dunks.
 
Thanks for your responses. Garden dust has been discontinued by Safers so I have been unable to locate any though I belive the mosquito dunks can be had. I will have a read on your journal StoneOtter though I will be taking a similar approach as suggested. Thanks
 
Thanks for your responses. Garden dust has been discontinued by Safers so I have been unable to locate any though I belive the mosquito dunks can be had. I will have a read on your journal StoneOtter though I will be taking a similar approach as suggested. Thanks
Dang! That stuff is my go to! Though I haven't had a gnat since I went away from barnyard manure and gone with llama poo compost. Edit: I contacted Safers to ask if they have an alternative for in soil use.
 
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