When one of my lettuce plants started wilting, I pulled on it and found I could just pull it straight out of the soil with no resistance. On the roots, I found these maggots. (You may need enlarge the picture a bit.)
Does anybody know what these are?
How likely is it that those are why the lettuce started dying?
Can they spread to other nearby potted plants?
What can you do against these?
Fungus gnat larvae - they have likely already spread to other pots. The adult is a small adult fly.
To controll them use BTi ( Bacillus thuringiensis israelensis) from mosquito dunks in your watering can.
Fungus gnats are a common problem for me whereever I have potted plants, but so far, they haven't managed to kill one yet. So far, I have been keeping them at bay with a combination of yellow sticky traps and, in extreme cases, an application of SF nematodes.
SF nematodes and sticky traps can reduce their numbers but they will always be present. BTi application to all of your pots will eliminate them in a few weeks.
Diatomaceous Earth (DE) ravages them too. Apply outside/don't breathe it in. Once it's in the soil, it will stay there for quite awhile and offers long lasting protection.
It cuts up the bugs!
They don't harm the plant, nor any people. They're just a nuisance when the plants are indoors, because then you've got bugs flying around indoors.
Watering with mosquito dunks tea, and sticky traps placed to touch the rim of the pot (since they like to walk up to the highest point before flying) worked to eliminate them for me.
Had the same problem on a chilli. In my experience, the chilli's/flowers were stunted.
I don't buy this. I just caught them going through the roots of a plant with severe root damage visible. Granted, this was in combination with overwatering, but still. There are also plenty of voices in the Internet saying that, if those larvae run out of other organic material in the soil, they will start eating plant roots.
Right, they're infesting the plant because of the root damage. You gave them a great food source. But if they run out of damaged roots, they won't start in on the healthy ones.