I bought a rhododendron this spring and planted it in my garden. For several months it seemed to be doing very well. Recently, I began to notice that some of the leaves on certain branches were developing brown areas. Others were wilting. Slowly, the entire branch would just sort of dry out and die. However, other parts of the plant continued to sprout new leaves and grow. This process seems to have picked up some steam in the last 2 weeks. More sections are looking unhealthy. I fear it is going to slowly die. Does anyone have any idea what the problem might be. I water regularly and fertilized it in the spring with an appropriate fertilizer. I do believe it may be getting a bit too much sun, but other plants in the neighborhood with similar sun are doing fine. (I am in NY)
I would suspect that you rhododendron is suffering from one of two things. The first is botrytis shoot blight or the second could be phytophthora root rot. To see and read for yourself, follow this link:
First, do you know your soil pH. The most important factor in achieving vigorous growth is an acid soil mixture high in organic content. Rhododendron and azaleas need an acid soil with a pH of 5.0 to 6.0, well mulched with organic material. Rhododendron thrive in a moist, well-drained, humus-filled soil, enriched with peat moss or leaf mold. Prepare the soil by thoroughly mixing equal parts of loam, coarse sand and ground oak leaves or redwood before planting.
If the soil is too alkaline, acidity may be increased by adding flowers of sulfur (powdered sulfur) or iron sulfate. I add 1 tablespoon of sulfur powder around the base of any plant showing signs of chlorosis. Do not use aluminum sulfate. Aluminum can build up in the soil to toxic levels eventually. One very common source of chlorosis is when lime leaches out of concrete, such as from a foundation or walkway, making the nearby soil more alkaline. This problem decreases each year as the concrete ages. An annual application of sulfur can compensate for this problem.
Sphagnum peat or peat moss is a super soil amendment. Researchers claim that plants planted in mixes containing sphagnum peat will resist disease better. The sphagnum peat in the soil does regulate the availability of water so the roots are not too wet, but also the sphagnum is said to provide protection against disease.
The following are some pathologies that could cause your problem:
A) If a leaf has brown areas with white spots , it probably has a local fungal infection of Pestalotia leaf spot . This is seldom controlled with fungicides and is best mitigated by good sanitation and avoiding excessive moisture.
B) Phytophthora causes the central vein of a leaf to turn brown and the discoloration extends to the petiole on tender new growth. The infections spreads outward from the midrib tissue and the leaf wilts. Infections are more severe on azaleas. Some varieties of rhododendron are vulnerable (Chionoides, Catawbiense Album, Nova Zembla) and some are resistant (Roseum Elegans, Scintillation, PJM). Control of the disease is difficult. Since the infection goes from the roots to the tips, when you see the symptoms it is too late. To prevent it, use a raised bed with lots of sphagnum peat moss. Prevention with fungicides and careful control of exposure to high humidity may be practical.
C) Botryosphaeria causes leaves to turn dull green and then brown and roll and droop . Cankers form on branches which may girdle the branch. Sanitation and applying a fungicide after pruning my provide some control.
D) Phomopsis symptoms vary from leaf spots to chlorosis and then browning of leaves which then wilt. Browning streaks extend down the stem to a wound. Fungicides should control an outbreak. Sanitation and applying a fungicide after pruning may provide control.
E) Your description sounds most like borers. Ends of branches die when rhododendron or azalea borer larvae tunnel in a stem. This affects the portions of the plant away from the roots from where the borer larvae is in the stem. Borers have done their damage when you see the wilting and usually it is best to cut off the affected region. The requires removing the damaged branch from the hole where the eggs were laid at the base of the dying branch to remove any larvae before they become adults and infect more plants. The parts that are cut off should be destroyed to kill the larvae that are in them. Borers are prevented by following a spray schedule (timing is very critical) for borers with chlorpyrifos or lindane. Your county agent can help you with this information.
F) Plants wilt and die slowly when their roots become blocked. There are two causes of this:
1) Root strangulation . This is best prevented by proper root pruning when planting . If the plant is not too far gone, it might be rescued by digging and removing the soil. Then cutting any circling roots that may be strangling other roots. The roots need to be opened up. On larger plants, some of the top must be removed to compensate for the weak state of the roots. Any time the roots are exposed, they must be kept moistened. Roots that dry out will die.
2) Phytophthora crown rot or wilt. This root rot is the major killer of rhododendron and azaleas. It develops when roots are growing in wet conditions. Plants infected with crown rot caused by the fungi Phytophthora have roots which become clogged with brown fungi internally. The roots get blocked and the plant wilts and dies. There is not much of any cure for crown rot. Some varieties of rhododendron are vulnerable (Chionoides, Catawbiense Album, Nova Zembla) and some are resistant (Roseum Elegans, Scintillation, PJM). Sphagnum moss and bark dust combined with good drainage seem to prevent crown rot, but do not cure it.
Hi timothy, wonder if you know that rhododendron like acid soils and hate lime or alkali soils, often you have to dig a very large hole and place the plant in an acid ericaceous soil It may be easier to use a very large pot. Also you must use ericaceous feed too. The normal symptom in alkali soils is for the leaves to go yellow then brown. You can buy a litmus paper from a garden centre to work out the ph of your soil, hope this helps
I do not know the PH level, but I have some azaleas that are doing very well. I also fertilized the area with an acid heavy fertilizer designed for acid loving plants.
Miracid is a water soluable fertilizer only helps temporarily but hurts in the long run since it is high in nitrogen. The best rhododendron fertilizer is HollyTone and it should only be applied in the spring or early summer.
If the plant does succumb, did it out and look at the roots. They may have been strangling each other when out got the plant. There also my be insect damage to the roots or root rot. Insects (weevils) would girdle the roots while the root rot (phytophthora) would make them mushy.
The number one killer of rhododendrons is water. The roots develop root rot.
Another thought, weed'n'feed or other weed killers will kill rhododendrons.
Poor drainage is the problem. Rhododendrons need moist soil, especially when transplanted. However conditions that are too moist will cause root rot, especially in hot weather and especially in certain varieties. That is one reason for using raised beds and sphagnum moss when planting. The raised bed improves drainage and the sphagnum moss helps moderate the moisture levels in the soil.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.