At some point, it comes to your attention that your ficus houseplant has mosquito-like insects flying around it and little white-looking worms (actually fungal gnat larvae) in the potting soil. Your first thought may be to immediately throw the plant out, but don't. While these pests can wreak havoc on your indoor plants, fungus gnats can be controlled by cultural (non-chemical) and biological methods.
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About Fungal Gnats
The first thing to know is that these little critters do not spread disease or pathogens to humans. Unfortunately, they are vectors to other plants, spreading foliage pathogens and diseases from one plant to another. Root rots such as Pythium or Fusarium, or foliage pathogens like Botrytis are a few such diseases gnats spread that can seriously damage or eventually kill off all your beloved houseplants.
Fungal gnats have about a four-week life cycle. According to Ohio State University, female gnats can deposit 100 to 300 eggs on the soil. Within four days, the eggs hatch into creamy-white-coloured larvae (which may look like white worms) and can grow up to 5 1/2mm long. Larvae feast upon the root hairs and plant stems, causing plants to wilt, yellow and decline in health. After 14 days they pupate, emerging about three days later as adults (mosquito-like flying gnats).
Yellow Cards & Potatoes
Yellow cards can help get rid of adult flying gnats (but not larvae) plaguing your ficus. Adhere a sticky yellow card to a Popsicle stick or straw and submerge it part way into the soil. Gnats, including other insects, are highly attracted to the colour yellow and will fly right into the sticky card.
Put one 1/2-inch square potato piece on the soil surface to trap larvae. After several of them burrow into the potato, simply throw the potato away.
Methods for Trapping & Killing Larvae
You can also biologically attack fly larvae with nematodes or mites. Apply Steinerema nematodes and water them into the soil surface to kill the larvae. Or, apply Hypoaspis miles (predatory mites) to the soil. After turning into adults (18 days), these mites kill upwards of seven fly larvae a day.
Thoroughly inspect a houseplant and its potting soil before buying it. If you see any flying gnats, put that thing of beauty down and walk away. Use yellow cards periodically, even if there doesn't appear to be a pest problem. Be careful not to overwater, as these pests thrive in overwatered soil conditions.
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