As an amateur grower, I've only got a few things growing, but still it was a huge disappointment today to find fruit flies were in everything except possibly my bell pepper sprouts. Everything else, even the new pot of carrot seeds, has fruit flies in them. That probably means not only do I have to discard the plants, but the soil too? There are too many for any trap or solution to rid them all, so I probably won't even try. The one thing I am trying to save is the pot of carrot seeds/sprouts since there can't be too many in that yet (only put it together a week ago and it's been mostly covered by a plastic bag to speed up germination). I've put a glass of vinegar beside the pot and in a new room on its own. Hoping I can at least save that.

The reason I'm posting, is I'm wanting to deduce why they started appearing in the first place. I have a good hunch it was the grass clipping tea, but can anyone more experienced give their thoughts on this? They started appearing roughly around the time I first tried the solution by spraying it on the now-invaded plants, namely a regrowing lettuce and at the base of some spring onions. It makes sense that they then jumped to the nearby carrot pot (damp soil and only a foot away from the lettuce). Does this sound plausible? I have read that simply having damp soil can attract the pests but I swear I didn't have any issue before spraying the steeped grass clipping tea (which was steeped outdoors without a lid so maybe they bred in that and I was literally spraying fly eggs onto my plants?).

I am thoroughly disheartened but hoping to find the motivation to start again.

Do you suppose they could be 'fungus gnats' and not fruit flies?  I think fungus gnats are a common problem in moist soil where plants are grown indoors.  One of the things that might help is a fan on low aimed at the plants to help dry out the soil surface a bit and maybe discourage the gnats themselves.  I usually run a fan over my seedlings to make them sturdier.  Probably shouldn't try this if they are already stressed though...other ideas in the links below.....

https://www.rodalesorganiclife.com/garden/fungus-gnat-control

https://www.smallfootprintfamily.com/controlling-fungus-gnats-organically

another thought...new seedlings don't usually need any sort of fertilizing until they are ready to transplant.  I don't think this would have caused the gnats/fruit flies to appear though.

It's definitely possible. The reason I suspected fruit flies is after reading they are drawn to rotting smells, and the grass clipping water certainly has a stench to it. Then there's the timing of when it started. My bell pepper sprouts are damp most of the day and the flies haven't found them yet. They've been around the longest too, so I don't think damp soil alone is/was the reason. I'll check out those links though. Thanks!

if fungus gnats get bt for mosquito and some predatory nematodes.

http://www.mosquitoreviews.com/bacillus-thuringiensis-bti.html

I found these flies are now in my two pots of seed potatoes. What do I do with these flies when the soil for these crops needs to stay damp?

L. Barry wrote:I found these flies are now in my two pots of seed potatoes. What do I do with these flies when the soil for these crops needs to stay damp?

I think I'm confused...are you growing these all indoors? even potatoes?

I think if it's fungus gnats or even fruit flies, neither would be a problem outdoors.

I hoped there would be something helpful in the links I posted and the bt link that Harry shared.  

The potatoes are outdoors far away from anything else that's growing. So they are appearing both indoors and out. I've tried the vinegar and dish soap solution but they aren't interested. Maybe they aren't fruit or fungus flies? I'd snap a picture but they are far too small.

L. Barry wrote:The potatoes are outdoors far away from anything else that's growing. So they are appearing both indoors and out. I've tried the vinegar and dish soap solution but they aren't interested. Maybe they aren't fruit or fungus flies? I'd snap a picture but they are far too small.

so maybe the big question is are they doing any damage that you notice?  and they are actually in the soil?  

This may not be great advice, but I tend to just wait and see when it comes to insects as many times a predator will show up when the population gets high enough....as with aphids and lady bugs.  I have enough plants though, that I don't worry about losing some.  

what is your climate like?  and is this the end of summer where you are also?  Adding your location could help...doesn't have to be exact, just ballpark area or zone even.

This sounds like what you are talking about I think....

http://homeguides.sfgate.com/rid-fruit-flies-breeding-plant-dirt-59391.html

Finding tiny fruit flies, or fungus gnats, loitering just above the surface of potted plant dirt is a common nuisance for indoor gardeners. These pests feed on the decaying organic matter and fungi in potting soil, although they do not cause any damage to plants. Fruit flies depend upon rotting organic debris to complete their life cycles, which is why you may also find them in the kitchen as they zero in on overripe fruits.

The article goes on to suggest a few safe methods to discourage both fungus gnats and fruit flies.  

I'm in zone 2 (sub tropical) and we're actually entering into summer now. Gold Coast in Queensland to be exact.

So they may not be harmful to plants? I hope so. I've never seen them on the plants directly (heard the larvae eat the root hairs though?) so maybe that's a good sign. I'll try the sand method next.

fungas gnats are not your friend and should not be considered a non issue.

I have seen these growing seedless tomatoes indoors.  I used to have diverticulitis.  They will harm your roots.  It is not the flier that are the problem in damage but the larva.

Fruit flies are generally from using items in compost that is not recommended most often.

In both situations, you need to break the life cycles and will take a minute or two.

L. Barry wrote:I'm in zone 2 (sub tropical) and we're actually entering into summer now. Gold Coast in Queensland to be exact.

So they may not be harmful to plants? I hope so. I've never seen them on the plants directly (heard the larvae eat the root hairs though?) so maybe that's a good sign. I'll try the sand method next.

I think I've heard that if the plants are healthy enough even the fungus gnats won't harm them....BUT, I don't have any first hand information.

I've never had either fly bother my seed start flats in the house or outside and we have had fruit flies at times in the kitchen, just not bothering the plants.

I like the idea mentioned in that last link of using a yellow card with something sticky on it (I wonder if fly tape would be yellow enough?).  

Do you suppose that there is just too much under decomposed material in your potting soil?  Apparently that's what both flies larvae feed on and if it's fungus gnats also some root hairs.

I found a flying isect trap at a thrift store and decided to try it in my raspberry house. It has 4 tiny blue LED lights and a fand that sucks the flies into a screen container.  It would fill the screen container with fruit flies and I would quickly unclip it and crush the flies with the little dish that came with it. Made good chicken feed.

If you are sprouting seeds or legumes and have any drain water from that, use it to water any soil where you see fungus gnats. I ran a hydroponic sprouter for years, and when I started having fungus gnats on overwintering plants I applied the water to their soil. Not only is it full of enzymes and some kind of growth factor, but the antifungal compounds on the seed casings, that are rinsed off when they sprout, will kill the fungus that feeds the gnat larvae. really, the sprouter water was almost as valuable as the sprouts!