So I decided to sow

[jerrytheplater]

Regarding Fungus gnats: I read the label on using Mosquito Dunks or Mosquito Bits for Fungus Gnats. Then I went onto the manufacturer's website and see their product will work for them. I tried it and it really did kill them. I didn't have the bits, just the dunks, so I broke one of the dunks up into bits, soaked it to make a tea, strained out the bits and watered with the tea. No more Fungus Gnats.

https://summitchemical.com/fungus-gnats-what-are-they/ Home Depot and other stores sell them.

[mmcavall]

Hi mmcavall, I also used to have terrible problems with fungus gnats but now just a few . I use diatomaceaous earth powder in my soil mix, have been for 20 years I think it keeps them away.
Could also be that I moved away from a area that had swarms of fungus gnats from neighbors raised planters . They would come through cracks in a fence. Very hard to grow seedlings with fungus gnats around.

Thank you keith. How do you add diatomaceus earth to the mix?

[mmcavall]

Regarding Fungus gnats: I read the label on using Mosquito Dunks or Mosquito Bits for Fungus Gnats. Then I went onto the manufacturer's website and see their product will work for them. I tried it and it really did kill them. I didn't have the bits, just the dunks, so I broke one of the dunks up into bits, soaked it to make a tea, strained out the bits and watered with the tea. No more Fungus Gnats.

https://summitchemical.com/fungus-gnats-what-are-they/ Home Depot and other stores sell them.

Thank you Jerry. To my surprise I found out that it is possible to find it here in Brazil (it is kind of expensive but maybe it will worth the price).

[MrXeric]

I sometimes get fungus gnats in my seedling propagation box over the winter when it's humid. Since I water the seedlings more frequently they don't have the chance to really dry out and kill the bugs, so I treat with imidacloprid. It's used as a sytemic but I believe it can work as a contact pesticide, especially on the larvae. One treatment is enough.

[keith]

I add it to the soil mix as I make it. Food grade is what you want about 5% by volume. If you use it wear a mask until its wet its a very fine powder. It shows up at the drain holes and on top of the soil, a white residue as a tiny crystalline structure. I've used it for 20 years at least but used to use a high fired pool filter type don't use that it contains silica bad for the lungs. Best for seedlings they get the worst of fungus gnat problems.

[mmcavall]

I sometimes get fungus gnats in my seedling propagation box over the winter when it's humid. Since I water the seedlings more frequently they don't have the chance to really dry out and kill the bugs, so I treat with imidacloprid. It's used as a sytemic but I believe it can work as a contact pesticide, especially on the larvae. One treatment is enough.

Thank you Mr. Xeric. I use imidacloprid, too. But perhaps my wet and hot climate makes the growth cycle of the insects shorter. I would probably have to use the insecticide every 10 days for... ever... I've tried but I always forget .. I dont work very well with this...

I add it to the soil mix as I make it. Food grade is what you want about 5% by volume. If you use it wear a mask until its wet its a very fine powder. It shows up at the drain holes and on top of the soil, a white residue as a tiny crystalline structure. I've used it for 20 years at least but used to use a high fired pool filter type don't use that it contains silica bad for the lungs. Best for seedlings they get the worst of fungus gnat problems.

Thank you, Keith...this is something I may try...

I'm collecting all these opinions to come back with a "infalible" (haha) plan.
Thanks

[LateBloomer]

I don't treat my fungus gnats... this is a bad idea if you have very few seedlings of a specific species but over 30+ seedlings most will survive without issue. I only have them when I start my seeds since the top layer is topsoil but once repotted into 100% mineral mix they just disappear.

From what I've experienced if the seedlings make it to 6 months the gnats will not kill them at worse they will only slow down growth a little bit. The cacti will produce different alkaloids to combat the gnats and make themselves less attractive to them. But some species seem to lack this ability like mammillaria boolii didn't 'combat' them naturally.

[mmcavall]

I don't treat my fungus gnats... this is a bad idea if you have very few seedlings of a specific species but over 30+ seedlings most will survive without issue. I only have them when I start my seeds since the top layer is topsoil but once repotted into 100% mineral mix they just disappear.

From what I've experienced if the seedlings make it to 6 months the gnats will not kill them at worse they will only slow down growth a little bit. The cacti will produce different alkaloids to combat the gnats and make themselves less attractive to them. But some species seem to lack this ability like mammillaria boolii didn't 'combat' them naturally.

Yes. They leave the seelings alone when they get older. The problem is I have seedlings of all ages all year round.

Not sure fungus gnaths are the main problem. I just decided to use the bag method with real individual bags...so if a pot have fungus gnaths or fungus the problem will not spread to the other pots.

[mmcavall]

Now I want to show what I have found when transplanting some seedlings.
They looked very stressed and the substrate looked very bad..
So I noticed theses injuries at the base of the seedlings. What can it be?
Fungus gnaths that gave up or died due to insecticide?

The mix has no grit, sand or gravel so the scars are not due to injuries caused by the substrate.

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[LateBloomer]

I have this I believe it is the beginning of rot that just didn't spread or kill the seedling. I would say it is caused by the substrate being too moist and those specific seedlings couldn't handle it.

I may be wrong so wait for other opinions.

[keith]

Scaria fly larva would hollow out the seedlings in hours so probably a slight rot which went away.