This same sugject was just discussed a few days ago, suggest you read a few of the more recent threads. The safest spray is neem.

Sarada, it sounds like fungus gnats, which are quite common in peat-based potting mixes, especially (but not exclusively) when kept very moist. Poor circulation can also contribute to their populations.

The larvae are what does the damage, by nibbling at tender roots. One very simple way to get rid of the larvae is by soaking pieces of one of those mosquito dunks in your watering bucket, and then using that water for your plants. Mosquito dunks contain a biological control called Bacillus thuringiensis-israelensis, which targets the larvae of specific insects, including mosquitoes and fungus gnat.

You can also put a layer of coarse sand over the top of the potting mix, making it difficult for the adults to lay eggs. Horticultural diatomaceous earth can be extremely useful, as well.