berrypilot
New member
So when I started growing outside this year for the first time in soil (I'm a hydro/coco indoor grower, so it's a very different experience!) I initially had a HUGE infestation of fungus gnats.
I didn't realize how badly I was overwatering my cannabis seedlings at first. I was soaking the young plants every two days in 5-gallon pots. I'm not sure what I was thinking, because I wouldn't do that indoors...
It felt like I noticed a fungus gnat one day, and then the next day my soil was CRAWLING with fungus gnats. They were everywhere. All over the pots, all over the soil, even just sort of buzzing around on the ground near the soil. I thought, ok, I'll stop overwatering them and they'll go away.
And seriously, drying the soil out well between waterings sort of brought down their numbers a little, but the moment I watered my plants again they came back with a vengeance.
I definitely needed more than to just stop overwatering my marijuana plants.
It was seriously a three-week struggle to get rid of the fungus gnats for good, and I wanted to share my experience with others who might run into this problem!
1.) Dusted the soil with diatomaceous earth using a powder duster to spread it evenly over the top of the soil and all over the sides of the pot and the ground next to the pots.
This was actually really effective. You could see that if a fungus gnat walked over the diatomaceous earth that they would die within moments. The soil was buzzing, but after applying this, 10 minutes later I couldn't see any gnats. Based on the complete and utter decimation, I assumed this was the end. Though by the next day I could still see there were tons of them
That being said, I think it brought their numbers down dramatically, and I re-applied about once a week until they were gone.
Conclusion: Very good at bringing down numbers, won't get rid of the infestation. Use alongside something else.
2.) Put up Yellow Sticky Traps
These are supposed to bring down their numbers by catching fungus gnats. They're naturally attracted to the yellow color, and then they get stuck and can't escape. Unfortunately, I staked these in the soil of my plants, and when I came back an hour later it had caught maybe one fungus gnat but also a bee My husband freed the bee and it was able to fly away, but no more sticky traps for me when growing outdoors!
Conclusion: Caught a bee in the trap So I don't think they're suited for outdoors
3.) Misted with Neem Oil using a hand sprayer to cover the soil evenly
The guy at the garden store recommended this and said it would kill all bugs (I told him it was for my roses!). I misted the soil with this. I didn't want to water the plants with it because I was afraid it might hurt the roots. I could see that it killed the bugs within a minute of contact, so I was also really hopeful about this one. I think the numbers were going down, and I was spraying this stuff everywhere, on the sides of the pots, around the ground, etc, but after a few days I felt like it wasn't doing enough.
When I had to water the plants, the fungus gnats came back maybe half as bad as the last time I'd watered. I decided to give up on the neem oil. I also heard from the guy at the garden store that it was a fungicide so I used it as a foliar spray in my roses that had black leaf spot, and I feel like it not only hurt the plant (it looked sad and droopy the day after being sprayed), the black spot actually got worse! That rose bush still looks terrible, and hasn't been making new roses. So I tossed the rest of it. Neem oil might be good for some things, but at least for me it wasn't effective at fungus gnats and seemed to cause problems with my other plants!
Conclusion: Seemed to kill fungus gnats instantly when they were sprayed, but they still kept coming back. I'd say it was mildly effective. It also hurt my roses when I sprayed them so I kind of hate neem oil now lol
4.) Mosquito bits in the water (PHed water right before giving to plants)
So I read about this one on the website. This stuff isn't really a pesticide, it actually is just bacteria that kills larvae of mosquitos, but apparently it's also effective at fungus gnats for some reason. Maybe they're related, or their larva are similar. Any ways. First I tried sprinkling it on the soil and then watering, but that didn't seem to do anything. Then I realized the website told you it was most effective if you actually put it in your water. So I dumped a handful of them into my watering jug, and let it sit for a day before I watered my plants with it (still PHing). At this point the plants are about 4 weeks old, and so I haven't given them any nutrients yet since they have some in the soil. I could tell the seedlings were growing slower than they should have because of either the gnats, the neem oil, or both. They had only 5 or 6 nodes by week 4 and were maybe 5 inches tall
After watering with this, I feel like the fungus gnats were MUCH more scarce. Like, instead of coming back with a vengeance like they normally did when I watered, they actually seemed to stay the same or even be less.
Conclusion: Didn't work when sprinkled on the soil, but did seem to help when I let the bits sit in the water overnight first
5.) SM-90 in the water at 1-2 tsp/gallon (I still made sure to PH the water)
So by the time I tried this, there were just a few fungus gnats buzzing around. It wasn't what I would consider an infestation anymore, but the gnats just wouldn't go away completely. I wanted them to be actually GONE. So I read in a forum somewhere that SM-90 is good at lots of bugs. Plus, it's supposed to be good for your roots on its own. However, I didn't see anyone online try it for fungus gnats. I'm not sure why I tried it since I couldn't find a single person who said it worked for fungus gnats, but I had been reading lots of good stuff about it and I thought, why not?
I contacted Nutrilife and they said it wouldn't kill good bacteria. So I started adding the SM-90 in addition to the Mosquito Bits in the water. The first time I watered the plants with the SM-90, I feel like they actually perked up a little by the next day. I do think it might actually be just good for them because they have been growing very well after I started! It might just be my imagination.
In any case, I haven't seen a single fungus gnat since I started with the Mosquito Bits / SM-90 combo in early June! Maybe it was the last legs of the infestation and they would have been gone anyways, but I just like how the plants look now. I'll eventually stop giving them the Mosquito Bits, too, but I plan on giving them SM-90 until harvest (now I'm just giving them 1 tsp/gallon since I'm not trying to kill anything anymore)
Conclusion: Seemed to be the thing that put the final nail in the coffin!
Repotted this cannabis plant into a raised bed with fresh soil - no fungus gnats in sight!!! About two months old now, and a month since the infestation was eradicated.
Final Conclusion: If I had a fungus gnat infestation again, I would...
Considering the circumstances, I'm still open to the idea that it may not have been the SM-90, and that's just what I happened to be using at the end! So that's why I'm curious if anyone here has tried it for fungus gnats?
I didn't realize how badly I was overwatering my cannabis seedlings at first. I was soaking the young plants every two days in 5-gallon pots. I'm not sure what I was thinking, because I wouldn't do that indoors...
It felt like I noticed a fungus gnat one day, and then the next day my soil was CRAWLING with fungus gnats. They were everywhere. All over the pots, all over the soil, even just sort of buzzing around on the ground near the soil. I thought, ok, I'll stop overwatering them and they'll go away.
And seriously, drying the soil out well between waterings sort of brought down their numbers a little, but the moment I watered my plants again they came back with a vengeance.
I definitely needed more than to just stop overwatering my marijuana plants.
It was seriously a three-week struggle to get rid of the fungus gnats for good, and I wanted to share my experience with others who might run into this problem!
1.) Dusted the soil with diatomaceous earth using a powder duster to spread it evenly over the top of the soil and all over the sides of the pot and the ground next to the pots.
This was actually really effective. You could see that if a fungus gnat walked over the diatomaceous earth that they would die within moments. The soil was buzzing, but after applying this, 10 minutes later I couldn't see any gnats. Based on the complete and utter decimation, I assumed this was the end. Though by the next day I could still see there were tons of them
That being said, I think it brought their numbers down dramatically, and I re-applied about once a week until they were gone.Conclusion: Very good at bringing down numbers, won't get rid of the infestation. Use alongside something else.
2.) Put up Yellow Sticky Traps
These are supposed to bring down their numbers by catching fungus gnats. They're naturally attracted to the yellow color, and then they get stuck and can't escape. Unfortunately, I staked these in the soil of my plants, and when I came back an hour later it had caught maybe one fungus gnat but also a bee
My husband freed the bee and it was able to fly away, but no more sticky traps for me when growing outdoors!Conclusion: Caught a bee in the trap
So I don't think they're suited for outdoors3.) Misted with Neem Oil using a hand sprayer to cover the soil evenly
The guy at the garden store recommended this and said it would kill all bugs (I told him it was for my roses!). I misted the soil with this. I didn't want to water the plants with it because I was afraid it might hurt the roots. I could see that it killed the bugs within a minute of contact, so I was also really hopeful about this one. I think the numbers were going down, and I was spraying this stuff everywhere, on the sides of the pots, around the ground, etc, but after a few days I felt like it wasn't doing enough.
When I had to water the plants, the fungus gnats came back maybe half as bad as the last time I'd watered. I decided to give up on the neem oil. I also heard from the guy at the garden store that it was a fungicide so I used it as a foliar spray in my roses that had black leaf spot, and I feel like it not only hurt the plant (it looked sad and droopy the day after being sprayed), the black spot actually got worse! That rose bush still looks terrible, and hasn't been making new roses. So I tossed the rest of it. Neem oil might be good for some things, but at least for me it wasn't effective at fungus gnats and seemed to cause problems with my other plants!
Conclusion: Seemed to kill fungus gnats instantly when they were sprayed, but they still kept coming back. I'd say it was mildly effective. It also hurt my roses when I sprayed them so I kind of hate neem oil now lol
4.) Mosquito bits in the water (PHed water right before giving to plants)
So I read about this one on the website. This stuff isn't really a pesticide, it actually is just bacteria that kills larvae of mosquitos, but apparently it's also effective at fungus gnats for some reason. Maybe they're related, or their larva are similar. Any ways. First I tried sprinkling it on the soil and then watering, but that didn't seem to do anything. Then I realized the website told you it was most effective if you actually put it in your water. So I dumped a handful of them into my watering jug, and let it sit for a day before I watered my plants with it (still PHing). At this point the plants are about 4 weeks old, and so I haven't given them any nutrients yet since they have some in the soil. I could tell the seedlings were growing slower than they should have because of either the gnats, the neem oil, or both. They had only 5 or 6 nodes by week 4 and were maybe 5 inches tall
After watering with this, I feel like the fungus gnats were MUCH more scarce. Like, instead of coming back with a vengeance like they normally did when I watered, they actually seemed to stay the same or even be less.
Conclusion: Didn't work when sprinkled on the soil, but did seem to help when I let the bits sit in the water overnight first
5.) SM-90 in the water at 1-2 tsp/gallon (I still made sure to PH the water)
So by the time I tried this, there were just a few fungus gnats buzzing around. It wasn't what I would consider an infestation anymore, but the gnats just wouldn't go away completely. I wanted them to be actually GONE. So I read in a forum somewhere that SM-90 is good at lots of bugs. Plus, it's supposed to be good for your roots on its own. However, I didn't see anyone online try it for fungus gnats. I'm not sure why I tried it since I couldn't find a single person who said it worked for fungus gnats, but I had been reading lots of good stuff about it and I thought, why not?
I contacted Nutrilife and they said it wouldn't kill good bacteria. So I started adding the SM-90 in addition to the Mosquito Bits in the water. The first time I watered the plants with the SM-90, I feel like they actually perked up a little by the next day. I do think it might actually be just good for them because they have been growing very well after I started! It might just be my imagination.
In any case, I haven't seen a single fungus gnat since I started with the Mosquito Bits / SM-90 combo in early June! Maybe it was the last legs of the infestation and they would have been gone anyways, but I just like how the plants look now. I'll eventually stop giving them the Mosquito Bits, too, but I plan on giving them SM-90 until harvest (now I'm just giving them 1 tsp/gallon since I'm not trying to kill anything anymore)
Conclusion: Seemed to be the thing that put the final nail in the coffin!
Repotted this cannabis plant into a raised bed with fresh soil - no fungus gnats in sight!!! About two months old now, and a month since the infestation was eradicated.
Final Conclusion: If I had a fungus gnat infestation again, I would...
- Stop overwatering
- Get diatomaceous earth and dust the soil once or twice a week
- Add 1 tablespoon of Mosquito Bits and 1 tsp SM-90 per gallon to the water and let it sit overnight
- PH the water right before giving it to your plants
- Repeat, letting soil dry out well between waterings, until the fungus gnats are gone
Considering the circumstances, I'm still open to the idea that it may not have been the SM-90, and that's just what I happened to be using at the end! So that's why I'm curious if anyone here has tried it for fungus gnats?
Do you think it adds nutrients to the soil? That was another thing I worried about, Could the diatomaceous earth be slowly releasing calcium, or something like that? I don't want something that might change the nutrient levels. That's why I repotted the plants in fresh soil after I was sure the gnats were gone. 🌱
