Sooty Mold

• Sooty mold is a byproduct of aphid or scale insect infestations. The insects excrete a sticky substance called honeydew that serves as a growing medium for the mold, which causes black patches on the surface of the leaves. Wash the plant with a hard spray of water to dislodge the insects and, if the water doesn't wash off the mold, use a soft cloth to wipe it off the leaves.
  
  

Fluoridated Water

• Dracaena plants are sensitive to the fluoride added to tap water. Symptoms of fluoride injury include yellow, brown or black spots on dracaena's foliage. In most cases, letting tap water sit uncovered overnight eliminates the fluoride and solves the problem. However, some water treatment plants use a different type of additive that doesn't dissipate. Check with your water provider or use well water, rainwater, purified or bottled water.
  
  

Fungal Infections

• Many fungus species attack dracaenas in containers and in the garden. Most create tan or brown spots that may have yellow halos. The tiny back spots that develop within these leaf spots are fruiting bodies produced by the fungi. As the infection grows and spreads, so do the leaf spots, and the black specks become more numerous on the leaves. The entire leaf may die. Your nearest cooperative extension office can usually diagnose a sample of the infected tissue and tell you which fungicide is appropriate to treat the infection.
  
  

Prevention

• Keep dracaena in bright light and make sure the plant gets good air circulation to help keep the leaves dry. Avoid overwatering and overfertilizing the dracaena. Always use fresh, sterile potting soil in clean pots when repotting container-grown dracaena. Use one part bleach mixed with nine parts of water to disinfect gardening tools. Prune dracaena plants in the garden to improve air circulation and water them at ground level rather than from overhead. Replace plants suffering widespread or severe infections. In the garden, an application of preventive fungicide before new growth appears in spring may protect the plants from infection.