How to avoid Fungus Gnats on my herb garden plants

What are Fungus Gnats?
Fungus gnats are small pests about 2 to 5 mm long, like many mosquitos. Although they don’t bite or sting, plant lovers don’t like them because they love to crawl and creep around on our plants and in our growing media. The larger ones also fly around, from plant to plant, and when we are around they like to fly in our face also. 
There are tons of varieties of fungus gnats around but most likely plant lovers and herb gardeners will have fungus gnats from either the Mycetophiliadae or Sciaridae family. Sometimes they are referred to as Black Fly or Sciarad fly.
Females mate within a few hours after leaving the pupa and begin laying eggs already after a few days. The tiny eggs are only 0,09 to 0,15 mm (so very hard to detect) and one female can easily lay 100-300 eggs.
These little blackflies are not only annoying but it is their larvae that hatch in moist growing media that cause most of the problems, especially to younger plants or seedlings.
The fungus gnats larvae primarily feed on organic material, algae and soil fungus. So you may think that is not a problem. True, but when there is a high quantity of larvae, they require other food sources including plant roots and stem tissue. They basically feed on your plants which creates wounds, which open up the gateway to secondary infections such as Pythium, Phytopthora and Fusarium.
Seedlings and younger plants will die, while the older plants could stop growing, causing the leaves to wilt and discolour, and uptake of water and nutrients will slow down.
The fungus gnats larvae are relatively difficult to find in the soil mix or in the stem tissue of plants. And when they feed on root hairs of newly planted crops, cuttings or seedlings it is hard to tell that the reduction in growth is caused by these little larvae.
This means that the damage to growing plants from the fungus gnats larvae goes very often unnoticed.
The chewing larvae damaging and wounding the plant provides a large possibility of diseases, which are actually the secondary cause of plant problems then and not the primary.
This leads often to confusion for the herb gardener about the cause and effect of why the plant is suffering.
In order to battle the fungus gnats larvae,we need to understand the lifecycle of a fungus gnat.