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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:

Popis potížíZpůsob odstranění
Bright yellow or bright green leaves, while the  nervation is darkJaundice (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 underSunstroke; replant into shadow or shade up
Leaves puffed with green blisters, otherwise yellowish surfaceMosaic 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 colourFrost 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 summerLack of water; needs quick and thorough watering
Leaves on scaly Rhododendron gaining red to brown stains, with little dip-spreading blisters and falling leavesRhododendron 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 leafLeaf spot caused by fungus. Needs spraying with organic fungicides
Leaves with grey tint and epidermis subsequently peels offMilky spore disease caused by fungi; burn the infected areas or remove the whole plant
Gent Azalea leaves with brown stainsCaused by fungus; needs spraying with Capten or Fundazol, 2x every 2 weeks from July to August
Azalea leaves with gnawed-off flat areasSlender rhododendron miner, tiny parasitical butterfly. Needs spraying with organophosphates (Metetion) or other insecticide
Leaves bitten off, twisted togetherThe responsible pest is moth caterpillar. Needs spraying with organophosphates
(Metetion) or other insecticides
Leaves bitten off at the edgesCaused by inchworm. Needs spraying with organophosphates (Metetion) or other insecticides
Leaves with irregular edge shapes; bitten-off curved shapes and gnawed budsBlack 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 outGlow-worm; repeated spraying using organophosphates is recommended
Azalea leaves are furled  and deformed; stunted sprouts, dried out budsStrawberry mite; remove infected sprouts, spray repeatedly with Actelic
Spotty, yellow-turning leaves, contaminated by sticky pickle, presence of whitefliesGreenhouse whitefly; repeated spraying with Actelic
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 offFungal infection; Kuprikol spraying
Flowers do not fully open and wiltPlant suffered from dryness or its buds were slightly freezed out; it is recommended to remove it to avoid infestation by pests
Vysazené azalky a rododendrony neuspokojivě rostouCracking trunk at roots, bark is peeling offFrost 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 colourFungal infection; needs soil aeration and application of Heryl 80 or Hermal
Planted Azaleas and Rhododendrons grow unsatisfactorilyWrong planting, plant inserted too deep, possible dried out ball; water well, provide shading on too sunny site, or, preferably, water with automatic irrigation