Rhododendrom Is Sick - Ask Extension
Why are parts of my rhododendron dying off? Is lack of water or disease? How can I treat? Thank you!
Knowledgebase
Rhododendrom Is Sick #785103
Asked March 25, 2022, 1:15 PM EDT
Why are parts of my rhododendron dying off? Is lack of water or disease? How can I treat? Thank you!
Baltimore County Maryland
Expert Response
Branch dieback on Rhododendron can be caused by an array of issues -- it could result from drought stress, overly-saturated or poorly-drained soil, wood-boring insect pests, or infection. It's hard to tell from symptoms alone since there is a lot of overlap in how these ailments present themselves. Typically, it's infection in either the branches or roots that begins after the plant was first stressed by either drought or too much soil moisture. Botryosphaeria canker is one example of a common pathogen; Phytophthora is another.
Rhododendron are best adapted to woodland conditions, and when planted by a house foundation, are more susceptible to stress due to the compacted soil and limited airflow. If these plants receive too much direct afternoon sun in the summer, that will make drought stress more likely, or it exposes them to added heat from the reflected/radiating warmth from the wall. Are the plants checked for soil moisture periodically during summer and autumn? Does a roof downspout empty nearby, or does the gutter overhead tend to overflow near their roots? Roots that stay too wet are deprived of oxygen and can die back, resulting in corresponding branch death as well.
All you can do for now is to trim out the dead/dying stems with the brown and curled foliage. Cut down to where the stem in question meets a healthy branch, leaving just enough of a small stub so the cut isn't flush with the wood so it can heal. (Leave perhaps a quarter-inch or half-inch stub.) Monitor the soil during the growing season for watering needs by feeling the soil moisture about five inches down, watering well when it feels fairly dry but delaying if it still feels moist. There is no fungicide or insecticide that would be effective, nor do the plants need fertilizer, although measuring the soil pH with a soil test would help determine if the plants would benefit from increasing soil acidity. We see a bit of chlorosis on one branch (signs of a nutrient deficiency in foliage, which can be affected by soil pH), but this is likely due to the health of that particular branch or a portion of the root system rather than a true soil deficiency since the rest of the foliage appears to be healthy.
Miri
Rhododendron are best adapted to woodland conditions, and when planted by a house foundation, are more susceptible to stress due to the compacted soil and limited airflow. If these plants receive too much direct afternoon sun in the summer, that will make drought stress more likely, or it exposes them to added heat from the reflected/radiating warmth from the wall. Are the plants checked for soil moisture periodically during summer and autumn? Does a roof downspout empty nearby, or does the gutter overhead tend to overflow near their roots? Roots that stay too wet are deprived of oxygen and can die back, resulting in corresponding branch death as well.
All you can do for now is to trim out the dead/dying stems with the brown and curled foliage. Cut down to where the stem in question meets a healthy branch, leaving just enough of a small stub so the cut isn't flush with the wood so it can heal. (Leave perhaps a quarter-inch or half-inch stub.) Monitor the soil during the growing season for watering needs by feeling the soil moisture about five inches down, watering well when it feels fairly dry but delaying if it still feels moist. There is no fungicide or insecticide that would be effective, nor do the plants need fertilizer, although measuring the soil pH with a soil test would help determine if the plants would benefit from increasing soil acidity. We see a bit of chlorosis on one branch (signs of a nutrient deficiency in foliage, which can be affected by soil pH), but this is likely due to the health of that particular branch or a portion of the root system rather than a true soil deficiency since the rest of the foliage appears to be healthy.
Miri
