How to Kill a Gnat Infestation on a Plant
- 1). Place cut potato slices onto the top of the soil to determine if larvae are thriving. Examine the underside of the potatoes daily to figure out the number of gnat larva that exist. Place the slices on the soil surface after each treatment to determine if you are killing the larvae.
- 2). Stop watering the plant to let the soil dry out completely. Allowing the soil to dry between each watering kills the larvae.
- 3). Place yellow sticky traps across the soil so that they lay horizontal. The traps are available at most garden supply stores and catch female gnats before they lay eggs.
- 4). Remove all freestanding water and organic debris from around the plant. Grass clippings, fertilizers and mulches allow the gnats to reproduce.
- 5). Apply an insecticide that contains Bacillus thuringiensis (Bti) to the plant to control the gnats. Insecticides with pyrethrins or pyrethroid also can control gnat infestations.
