Fungus gnats belong to the insect families Sciaridae and Mycetophilidae. The former consists mostly of gall midges and dark-winged fungus gnats while the latter comprised of the small flies known for their well-formed but spiny legs and strongly humped thorax. Adults are grayish-black, look like mosquitoes and prefer to fly around houseplants and inside damp greenhouses. Their larval stages are especially harmful to crops because they feed on the tender roots of plants. Learn how to remove these pests organically below.
Reduce Your Watering
When you spot fungus gnats in your greenhouse, stop watering so that water level can recede to between 1 and 2 inches. This is helpful because it makes the soil inside the greenhouse a hostile environment for the larvae. Fungus gnats avoid such soils when looking for places to lay eggs and, eggs laid in such soils do not develop into larvae.
Avoid Peat Moss
If you grow during the winter, avoid using peat moss or any other such water-holding organic material because they may provide a favorable environment for the fungus gnats to lay their eggs.
Preferably, you should mix the nematodes with fertilizer used for top dressing. Mixing nematodes with fertilizer help ensure uniform distribution. Beneficial nematodes such as Heterorhabditis Bacteriophora, Steinernema Feltiae and S. Carpocapsae are suitable for killing insect pests in greenhouse kits because they penetrate the larvae of fungus gnats and release bacteria that feed on the larvae from the inside out.
Bacillus Thuringiensis Bacteria
Bacillus Thuringiensis is effective in killing fungus gnats. It may take more than one application but the bacteria will eventually eliminate all the larvae of fungus gnats.
Diatomaceous Earth is a soft sedimentary rock in powder form kills fungus gnats by dehydrating them. However, it is only effective if it remains dry.
Plants are able to control fungus gnats. However, they are less effective compared to the above methods. You can use hardy Cape Sundew plants and butterwort. Note that these plants require a lot of sunlight so if you intend to use them to control fungus gnats then you should set your greenhouse kits in a manner that exposes them to the sun.