Rhododendron problem at Towson home

Asked April 5, 2017, 7:40 AM EDT

I'm attaching pictures of a 60+ year old rhododendron that appears to be dead in parts and unhealthy in others. The plant showed signs of deterioration at the end of last fall. At the very end of Spring 2016 I fertilized this plant with Holly Tone, and I'm afraid I over fertilized; a healthy white pine died after the same application and some pruning. Can you please give me your recommendation as to what I should do in order to salvage, if possible, any parts of the plant. Thank you very much. UMD class of 1967

Baltimore County Maryland

1 Response

Last fall was very dry and that drought stress can predispose rhododendrons to disease. Our plant pathologist sees a small amount of Botrosphaeria.
We suggest (on a dry day) pruning out any dead branches, back to healthy tissue.
Old rhodies normally respond pretty well to a good pruning.

In times of drought, or when we don't get about an inch of rain a week (a tuna can in the vicinity can help monitor), offer the plant a long, slow drink.
Here is more information:
Botryosphaeria Dieback (Botryosphaeria dothidea)
This is the most common disease of rhododendron in the landscape. A typical symptom of this fungal disease is scattered dying branches on an otherwise healthy plant. Leaves on infected stems turn brown, then droop and roll inward. These leaves often lay flat against the stem and will remain attached. The pathogen can infect all ages of stem tissue through wounds, pruning cuts, and leaf scars. Heat, drought stress, and winter injury can increase disease incidence. Cankers on branches can gradually grow through the wood until the stem becomes girdled. Diseased wood is reddish brown in appearance. Discolored wood viewed in longitudinal cross section often forms a wedge that points toward the center of the stem, and the pith may be darker brown than the surrounding wood.
Management: Fungicide treatments are not an effective disease control option. Plants should be grown in partial shade, with mulch and kept well watered during dry periods. All dying branches should be promptly pruned out in dry weather and all discolored wood should be removed. Plants should also be protected from rough treatment during maintenance activities to prevent unnecessary wounds.

We don't think this is related to the problem with your pine, and are also not convinced that your fertilization played a role.