Rhododendrons are members of the Ericaceae family and are frequently used shrubs that enhance any landscape. According to the University of Kentucky, College of Agriculture diseases in rhododendrons are usually the result of poor growing conditions. These shrubs grow best in locations that provide partial shade and protection from the late day sun and wind. Reducing stress from heat or drought reduces the likelihood of disease.
Root Rot - Root rot commonly affects rhododendron. Serious fungal diseases such as Phytophthora root rot, are difficult to control and are most common in areas where there is a high level of moisture in the soil and warm soil temperatures. This fungal disease is often severe in areas where water collects around the plant's roots. The symptoms associated with Phytophthora root rot in rhododendrons includes slow plant growth with pale green foliage, failure to grow and dying within a few years. Some rhododendrons may wilt and die without warning. Root rot causes plant roots to turn reddish-brown and become brittle, states North Carolina State University, Plant Pathology Extension. Preventing root rot before it occurs is important, because chemicals are often not effective at controlling the condition once it appears. Avoid purchasing rhododendrons that lack green colour, have discoloured roots or are wilted.
Nematodes - Rhododendrons are particularly susceptible to nematode infestation. Infested plants suffer damage as the leaves turn yellow and plants are stunted. Failure to respond to treatments such as fertiliser is common with nematode infestation. Rhododendrons gradually die from this condition, as there are no chemical treatments available to control nematode infestations on rhododendrons. Preventing nematode damage is best accomplished by providing good growing conditions, water and partial shade.
Botryosphaeria Dieback - According to the University of Kentucky, College of Agriculture, one of the most common rhododendron diseases is Botryosphaeria Dieback. This fungal disease often attacks plants within the first few years after transplanting. Symptoms associated with Botryosphaeria Dieback in rhododendron plants include the growth of dead branches among healthy branches and the leaves on dead branches may roll downward and turn brown. Infection often begins at pruning wounds or leaf scars. Reducing plant stress is important to preventing Botryosphaeria Dieback in rhododendrons. Shade the plants from hot afternoon sun and provide them with plenty of water. Removing dead branches helps prevent the spread of the disease.