The larvae feed on dead roots and leaves, but sometimes consume tender new roots.

Do not over water plants. Keep growing areas as dry as you can.

pyrethrin, an organic pesticide if you have a major problem.

Adult fungus gnats are more of an annoyance then anything else. When they lay the eggs and their babies eat your young roots is when you have a problem.

Root rot is what attracts them. You are likely over watering. Put those jiffy pellets in soil or other growing medium as soon as they sprout the seeds.

I have never lost plants becase of them so do not panic.