Honey Dew Fungi

• Honey dew fungi is disease that thrives in humid soils and causes the leaves of holly plants to wilt and fall from the plant. Toadstools around holly plants in combination with wilted leaves are signs that honey dew fungi has infected a plant.
  
  

Tar Spot

• Tar spot is a fungal disease that attacks holly bushes in cooler seasons. The fungus of tar spot causes yellow spots in holly leaves, which eventually turn brown then black. Bush leaves affected by tar spot should be destroyed according to the University of Mississippi Extension Service.
  
  

Mold and Mildew

• Sooty mold is a fungus that grows on the honey dew, or excrement, that aphids leave behind on the holly leaf. It can easily be washed off holly plants with a garden hose. Powdery mildew appears on holly leaves as a white dust and can also be sprayed off plants with the addition of some light soap.
  
  

Fungicide

• After diagnosing holly bush leaves for disease, it is important to apply a broad spectrum fungicide to prevent contamination of other plants. By applying fungicide to affected holly bushes, it may be possible to save not only contaminated bushes but also neighboring plants.
  
  

Weather Effects

• Holly bushes damaged by cold weather or exposed to dry weather are more susceptible to leaf disease. As a preventative measure, regularly check damaged plants for any signs of fungus or changes in leaf color.