Leaf Spot

• Soft, small brown-leaf spots are a common problem when growing Dieffenbachia. Usually, an adjustment of the cultivation practices amends the problem. Misting plants with water to increase humidity causes leaf spot because the water remains stagnant on the leaves. This promotes bacteria or fungus. Leaf spot can also occur if there isn't enough light or if the air circulation is poor. Remove all infected areas to prevent further infection of healthy leaves. Also, increase the air circulation and lessen humidity by not crowding plants close together, or place a fan close by the plant. When misting, do it early in the morning and check that it dries within 10 minutes. Improve lighting if necessary.
  
  

Crown and Root Rot

• Crown and root rot is the most common disease found in all houseplants and dumb cane is no exception. It's caused by improper watering and allowing the soil to remain too moist. Letting the plant constantly sit a saucer of water causes root and crown rot. Identify this disease by stunted growth, brown areas on the leaves, wilted leaves and brown and slimy roots that smell foul. Allow Dieffenbachia amoena to dry out between waterings, use well-draining soil and don't leave it sitting in a saucer of water.
  
  

Aphids and Ants

• Aphids are small insects that come in a variety of colors including yellow, orange, pink, green, brown, black and white. They form in clusters to suck plant juices from the leaves of the dumb cane, which distorts the leaves, turns them yellow and stunts plant growth. Aphids excrete honeydew, a sticky, sweet substance that ants feed on. Oftentimes ants will farm aphids by transporting them to the plant to feed so the ants can feed on the honeydew. Honeydew also breeds sooty mold, a black fungus that blocks photosynthesis. Remove aphids by hand or with a strong stream of water. Insecticidal soaps and wiping the leaves with alcohol are also effective removal methods.
  
  

Mealybugs

• Mealybugs are white, cotton-like pests that cause damage similar to aphids. They suck the plant juices from the leaves and excrete honeydew. Look for mealybugs in the plant's cracks and crevices like where the leaf and stem meet and in unfurled leaves. Mealybugs are immobile for most of their lives but reproduce copiously and infestations occur quickly. Wipe the leaves with alcohol to remove the mealy bugs and their eggs, or use an insecticidal soap mixed with neem oil. Repeat treatments every few days for at least two to three weeks.
  
  

Mites

• Tiny red spider mites live on the underside of dumb cane leaves and create small webs. Spider mites suck the leaf cells dry, which produces yellow, speckled feeding marks and causes the leaves to drop. These dieffenbachia pests thrive in warm, dry conditions. Use an insecticidal soap spray to get rid of the spider mites and horticultural or neem oil to kill the eggs. Increase humidity by lightly misting the leaves, using a humidifier or placing the plant's container on top of a tray of rocks with water poured over the rocks. As the water evaporates, it cloaks the plant in humidity.