Types

• Fungus gnats are flying insects that feed on the matter in the potting soil of houseplants. These pests resemble mosquitoes in their adult form, typically measuring 1/8 inch in length. Fungus gnat larvae are tiny, translucent worms that are often seen in the top 2 inches of plant soil.
  
  Aphids are tiny insects that are often bright colors such as pink, green, red or yellow. These pests feed on the leaves of plants, extracting plant sap. Damage to houseplants can occur if a large number of aphids are feeding on the plant.
  
  

Effects

• Homeowners may first notice fungus gnats when they move or bump their houseplant, causing adult fungus gnats to swarm. Upon closer inspection, fungus gnat larvae may be seen in the top layer of potting soil. Fungus gnats feed on plant roots and root hairs, resulting in scarred plant roots. Adult fungus gnats do not sting or bite, but they are bothersome when they swarm.
  
  Aphids place their mouthparts into plant leaves, causing leaves to become flecked or speckled. Houseplants with aphid infestations may also develop distorted stems or curled leaves. Feeding on excessive amounts of plant sap often causes aphids to excrete a sticky substance known as honeydew, resulting in sooty mold development. Sooty mold is best described as a coating of black fungus on the leaves of houseplants; it is caused by fungi sticking to honeydew. Sooty mold is not dangerous to the health of houseplants, but it is an unsightly, sticky mess indoors.
  
  

Cultural Control

• Avoid overwatering your houseplant to discourage the development of fungus gnats, as they thrive in wet soil conditions. Use sterile potting soil to avoid fungus gnat development and repot plants with clean soil after a few months, once the soil begins to break down and retain large amounts of water. Allowing your plant soil to dry completely before watering can help reduce fungus gnat development.
  
  Aphid infestations may be difficult to diagnose, because aphids are very small and difficult to see without a magnifying glass. Inspect the undersides of plant leaves for the pests, as this is where aphids congregate and feed. Washing your houseplant with a hard stream of water from the shower or garden hose twice each week may eliminate or control aphids by knocking them from the plant. Avoid using nitrogen-rich fertilizers, as these products promote the growth of new plant tissue, which is a favorite of aphids.
  
  

Chemical Controls

• Combining cultural control methods with chemical products may help control fungus gnats in your houseplants. Applying insecticidal sprays labeled for use on gnats or flying insects usually keeps fungus gnat populations low.
  
  Aphids are often successfully controlled with the use of horticultural oils. These products coat the insect, killing it. Apply horticultural oils to your houseplant, completely covering the plant and concentrating on the undersides of leaves for best results. Horticultural oils also help loosen and remove sooty mold fungi, which are a common result of heavy aphid infestation.