Diseases and pests of rhododendrons

Rhododendrons and Azaleas are still only decorative woods, therefore they are affected by a whole range of pests and diseases. Sometimes the problem is grave, other times, in order to remove it, it is only needed to conduct a little action. In the table below You can find a description of problems along with means of their solution:

Bright yellow or bright green leaves, while the  nervation is dark

Jaundice (chlorosis) cased by insufficiently sour soil. The main cause lies in the shortage of available iron which is necessary for chlorophyll creation. The problem is solved by the application of ferric ammonium citrate or iron calaates into soil or on a leaf



Leaves gain yellow to brown colour, sometime with crack on the edges, partially rolled under

Sunstroke; replant into shadow or shade up



Leaves puffed with green blisters, otherwise yellowish surface

Mosaic disease caused by a virus. Spread by aphids. Remove and burn the infected plant, or treat with Pirimor-like insecticide



After winter, leaves are cracked along the main vein, or, more frequently, with irregular crack on the edges, with leaves of bright and later brown colour

 Frost damage. Frozen leaf burnt by the sun. If the damages are great, change the site or use a cover for winter time



Leaves wither in summer

  Lack of water; needs quick and thorough watering



Leaves on scaly Rhododendron gaining red to brown stains, with little dip-spreading blisters and falling leaves

Rhododendron disease caused by fungi. Infected leaves must be burned. Spray with Dithane, repad 2-3x



Leaves with irregular, dark brown-red stains on the back side of the leaf

 Leaf spot caused by fungus. Needs spraying with organic fungicides



Leaves with grey tint and epidermis subsequently peels off

 Milky spore disease caused by fungi; burn the infected areas or remove the whole plant



Gent Azalea leaves with brown stains

Caused by fungus; needs spraying with Capten or Fundazol, 2x every 2 weeks from July to August



Azalea leaves with gnawed-off flat areas

 Slender rhododendron miner, tiny parasitical butterfly. Needs spraying with organophosphates (Metetion) or other insecticides



Leaves bitten off, twisted together

The responsible pest is moth caterpillar. Needs spraying with organophosphates
(Metetion) or other insecticides



Leaves bitten off at the edges

Caused by inchworm. Needs spraying with organophosphates (Metetion) or other insecticides



Leaves with irregular edge shapes; bitten-off curved shapes and gnawed buds

Black vine weevil – infested by its larvae; solved by Thiodane or Furadan spraying



Silvery-grey leaves that later turn yellow and fall off opadávají

Infested with thunderflies, tiny sucking insects; repeated spraying with organophosphated is recommended



Leaves full of small dots; turn white and dry out

Glow-worm; repeated spraying using organophosphates is recommended



Azalea leaves are furled  and deformed; stunted sprouts, dried out buds

Strawberry mite; remove infected sprouts, spray repeatedly with Actelic



Spotty, yellow-turning leaves, contaminated by sticky pickle, presence of whiteflies

Greenhouse whitefly; repeated spraying with Actelic



Abnormally thicker and enlarged Azalea leaves

Azalea gall caused by fungus; remove and burn leaves along with sprouts, spray with organic fungicide



Black leaves and sprout, sooty and viscid surface

Black leaf disease caused by fungus; wash the leaves with stream of water and then spray with Captan



Flower buds getting brown colour and not blooming

Frozen buds



Flower buds getting brown and dying off

Fungal infection; Kuprikol spraying



Flowers do not fully open and wilt

Plant suffered from dryness or its buds were slightly freezed out; it is recommended to remove it to avoid infestation by pests



Cracking trunk at roots, bark is peeling off

Frost damage in the time when a sap moves from roots to the crown; it is recommended to treat with grafting wask, or alternatively cut off (will germinate again)



Root stems of young Rhododendrons show brown or black colour

Fungal infection; needs soil aeration and application of Heryl 80 or Hermal



Planted Azaleas and Rhododendrons grow unsatisfactorily

Wrong planting, plant inserted too deep, possible dried out ball; water well, provide shading on too sunny site, or, preferably, water with automatic irrigation



 Have a look also on záchrana Rhododendronu, maybe You are trying to solve the same problem and our solution may help You.


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