University of Maryland Extension

Diagnostic Chart of Azalea and Rhododendron Problems

Symptoms

Details

Possible Causes

Leaf YellowingTowards interior of plantOlder leaf drop (normal)
Iron or magnesium chlorosisHigh soil pH and nutrient deficiency
Leaves may also have sooty mold (black coating)Azalea Bark Scale
Brightly colored, yellow-orange spotsAzalea Leaf Rust
Leaf Stippling (tiny spots)Whitish spots on upper surface of leaves; black spots on the lower leaf surfaceLace Bugs
Leaf Mottling (irregular marks or blotches)Margins of leaves cup, lower leaves covered with honeydew, then sooty mold; flat, oval transparent insects on the lower leaf surfaceAzalea Whitefly
Leaf DistortionSwollen green or white puffy areas on newly expanded leaves or flowersExobasidium Leaf and Flower Gall
Leaves roll and droopWater Stress
Leaves Eaten or ChewedNotching of leaf margins; interior leaves show most damageBlack Vine Weevil
Notches chewed in leaf marginsTwo-banded Japanese Weevil
Branches or entire plants may be defoliatedAzalea Caterpillar
Blotches on LeavesBlotch mines on leaves of azalea in MayAzalea Leafminer
Spots on LeavesVisible on upper leaf surfaceVarious Fungal Leaf Spots
Leaf ScorchMargins of leaves turn brown in winter or springWinter Injury
White Coating on LeavesMay be on upper and lower leaf surfacesPowdery Mildew
Flowers AffectedSmall, water-soaked spots enlarge rapidly, cause flowers to collapse and feel slimyOvulinia Petal Blight
Swollen areas on buds, flowers and petalsExobasidium Leaf and Flower Gall
Failure to FlowerSudden temperature drop in fall, unusually cold winters, or spring freezeWinter Injury
Branch DiebackScattered dying branchesBotryosphaeria Dieback
Leaves on scattered branches wilt, roll and turn brownPhytophthora Dieback
Wilting of leaves and twig diebackRhododendron Borer
Wilting terminals and diebackRhododendron Stem Borer
Entire Plant DiesEarly symptoms may include wilting, shoot dieback,Phytophthora Root Rot
As above, result of larvae feeding on roots and crownBlack Vine Weevil and Two-banded Japanese Weevil
Plants recover after irrigationWater Stress

Additional Resources

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