Fungus gnats

Fungus gnats or sciarid flies are a common pest in many greenhouses all over the world. The larvae don’t only feed on organic material in the soil. They can also cause damage to small roots of cuttings, seedlings and young plants in nurseries and in potted plants. As this pest is active all year round, now is the time to react with biological control.

What damage can fungus gnats cause?

• The larvae feed on rotting organic material such as algae and mould, but also on living plant material such as root and stalk tissue.
• The larvae pierce into the root or the stalk of cuttings, seedlings or young plants.
• Secondary plant diseases such as Pythium can enter and spread, due to which the plant wilts and the growth slows down. Unfortunately, the plant can even die.
• Fungus gnats can be a real pest as they create a large swarm under optimal conditions.

How to control fungus gnats?

To monitor adult fungus gnats, you can rely on Biobest’s Bug-Scan^® Yellow.

For biological control of the larvae in the soil, you can introduce:

• Soil dwelling predatory mites such as Hypoaspis-System;
• Soil dwelling rove beetles such as Atheta-System;
• Beneficial nematodes such as Steinernema-System.

What are the characteristics of fungus gnats?

• The eggs of 0.25 mm are deposited on the soil in humid areas with organic material.
• Larvae are present in the growing media near the roots. Full-grown larvae are about 5 mm long, transparent with a distinctive black head. They pupate in the soil.
• The pupae are 2 to 5 mm long and yellow to brown in color.
• The adults of 3 to 5 mm are dark flies with long, slender antennae and long legs. Their wings have a Y-shaped venation.
• Adults are particularly spotted in warm and humid areas of the greenhouse near the plants.

What about the fungus gnats‘ life cycle?

• Fertilized females lay 50 to 200 eggs. These eggs hatch in 2 to 3 days.
• Fungus gnats have 7 development stages: egg, 4 larval stages, pupa and adult.
• It takes them about 3 to 4 weeks to develop from egg to adult at temperatures above 24 °C/75 °F. The development stops at temperatures below 10 °C/50 °F and above 35 °C/95 °C.
• Adults only live up to 1 week.