Do your house plants have little mosquito-like insects occasionally, or regularly, flying around them? If you experience these little plant pests, your potted plants most likely have fungus gnats. Fungus gnats are small insects (1/8 to 1/10 inch long) that are common in high-organic-matter houseplant soils that are kept moist. These insects do not bother humans or pets. However, the larvae can injure plants by feeding on the roots. There are a number of symptoms of larval damage from fungus gnats which includes sudden wilting, loss of vigor, poor growth or yellowing of leaves. The best means of preventing fungus gnat problems is to avoid overwatering. Existing infestations can be controlled with Bacillus thuringiensis v. israelensis, which is found in the product Knock-Out Gnats. Beneficial nematodes can also be utilized to control the fungus gnat. Kansas State University reports that the species Steinemema feltiae is especially effective.
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