Causes

• Aphids, mites, thrips and scales make leaves curl, as do viral diseases. Using the wrong pesticides or soil contaminated with chemicals causes this problem as well. Low humidity or light, along with improper watering or temperature cause leaves to curl, according to Texas A&M University Extension.
  
  

Identification

• Check the growing conditions of your plant against suggested conditions. Many house plants are tropical and need direct, bright light for several hours every day. Most house plants need thorough watering, with moist soil that is not waterlogged. Allow soil to dry to a depth of 1/2 inch between watering. Plants preferring high humidity do well when placed in a pebble-filled tray containing water. Viral diseases are often accompanied by yellow streaks or spots on infected plants. Thrips, aphids and scale insects can be seen on plants, while mites are too small to be seen, but cause curling mainly on new plant growth. Leaves, buds and flowers often turn black on mite-infested plants also.
  
  

Solution

• Provide proper growing conditions for your plants at all times to prevent problems caused by improper conditions. Discard a house plant with a viral disease, suggests University of Kentucky Extension. ) Wash insect-infested plants with water or rubbing alcohol, apply insecticidal soap, or remove insects by hand. Snip off infected portions of mite-infested plants as needed. Always use clean potting soil and read labels of any chemical before applying it to plants.