Gnats on an Amaryllis

Fungus Gnats

• Adult fungus gnats lay up to 200 eggs in their 10-day lifetime. Larvae hatch, eat amaryllis roots and mature within a week. Often fungus gnats infest amaryllis plants because you try to induce blooming with warm temperatures and watering; moist, warm environments are optimal breeding grounds for fungus gnats. Noticing early signs of a fungus gnat infestation prevents the overall health decline of the amaryllis.

Symptoms

• Symptoms of fungus gnat damage consist of leaf yellowing, defoliation and stunted growth. Fungus gnat droppings contain disease-causing fungal spores such as Pythium, Botrytis and Verticillium. One way to tell if your amaryllis has been infested is to leave a piece of potato on top of the soil. Larvae work their way through the soil to feed, so you might see small white worms eating the potato piece. You also can look for trails on top of the soil left behind by the larvae.

Chemical Treatment

• You can treat fungus gnat larvae with a systemic insecticide imidacloprid. You place this pesticide around the plant in the soil. Over time, the insecticide releases a toxin that is absorbed by the amaryllis plant. When larvae eat the plant, they ingest the toxin. It is also important to kill off adult fungus gnats with a foliar pyrethroid-based insecticide. When spraying your amaryllis, take the plant outside so you don't breathe in the insecticide. Apply the insecticide evenly over the plant.

Replanting

• Remove old potting soil to reduce the amount of larvae eating the amaryllis bulb. Replant using a well-draining potting medium. You may prevent gnats in amaryllis plants by spreading gravel over the top of the soil. Gravel prevents fungus gnats from laying their eggs. Make sure that the layer of gravel is at least 1 inch thick. You can use use a gravel color that complements your amaryllis' blooms.