Rhododendrons used to be one of my favorite plants, as they are both beautiful and low maintenance….or so I thought. For the last several weeks I have been gradually deadheading the ones in my yard and am starting to share my experienced gardener friend’s point of view: ” I just hate them. And their sticky, messy claws.” Being up close and personal with the plants on a daily basis has allowed me to notice that many of mine are not all doing well at all.
Luckily, one of my neighbors lent me a lovely brochure called “EB-1229 – How to Identify Rhododendron and Azalea Problems“, which is also available online. It is full of informative colored photos and descriptions of many of most common illnesses that afflict rhodos and azaleas, lists of symptoms, possible causes and how to solve it. Some of these illnesses are similar to people: nutrient deficiencies, wet feet, viruses, insects, fungus, chemicals, sunburn. After a few pages into this brochure I started to feel the same crazy buzz I get when self-diagnosing myself with rare diseases on the internet.
I have summarized a few highlights below for future reference.
| Problem | Symptom | Cause |
| Marginal leaf necrosis | Upper leaves brown, burned back from tips and or edge towards the middle rib or middle of the leaf | Cold damage, drought, high amts of salts in the soil caused by excessive use of soluble fertilizers, root damage, nutrient deficiency. |
| Iron or manganese deficiency | Marked yellowing, on leaf parts, especially between veins of new leaves. | Overly alkaline soil, lack of iron or manganese in soil, lack of sufficient air space, poor drainage/compressed soil |
| Heat damage | Brown indistinct blotches, mostly on the central portions of top leaves. | Sun scald* |
| Viral diseases | Bright yellow to red-brown rings, spots and blotches on leaves. | No cure! Replace plant! |
| Nitrogen deficiency/wet feet | Overall yellowing of leaves, generally more prevalent on older and lower leaves | Nitrogen deficiency, wet feet, early symptom of poor drainage. |
| Leaf senescence | Older leaves will turn yellow and or brown and fall off the plant. | NORMAL! Loose leaves 1 – 3 yeears after they first emerge. |
| Chemical injury | A variety of leaf discolorations. | Herbicides and other chemicals. |
| Cold response/leaves | Drooping, rolled leaves | Cold weather |
| Indementum | Matted wooliness present on the surface of the leaves (often the underside) or twigs. | Normal! |
* interestingly, the rhodos on the north of the house, formerly shaded by the hemlocks, have this. Hopefully they will survive….
kalegrower 