Phytophthora Root Rot

• According to North Carolina State University, this root disease is a common problem in landscaping and nursery situations. It is caused by Phytophthora cinnamomi, a species of water mold, requires laboratory testing to diagnose and mostly affects small roots. In nurseries, it can be controlled using chemical treatment, but this isn't advisable in landscaping situations.
  
  

Annosus Root Rot

• Annosus root rot mostly occurs in cypress trees in landscaping, and is spread by a fungus that lives in pine and other conifer stumps. It affects nearby trees through root contact, and can slowly kill a cypress tree. There are no effective control measures once a tree has been infected, but removing conifer stumps immediately after cutting can help prevent the fungus from spreading.
  
  

Knees

• Cypress trees are notable for their unusual root structures, called knees, which develop in very wet soils and bog situations. These can be unattractive and inconvenient in landscaping. Texas A&M University website recommends reducing watering at the first sign of knees. Do not cut these root structures back, as this can encourage disease.