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Azalea and Rhododendron Problems

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Here is a list of common azalea and rhododendron problems and methods for treating and preventing them.  

Azaleas and Rhododendrons belong to the genus Rhododendron.  While they require the same light, acidic soil and growing conditions, they are very different in appearance.  Azaleas having smaller leaves and come in both evergreen and deciduous varieties.  The rhododendron genus cannot withstand windy or exposed locations.

There's also a section on how to deadhead and prune these shrubs below.  At the bottom of this page is a list of the hardiest Rhododendrons and Azaleas to grow.

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Insects and Mites

ProblemSymptomsControl

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Lace Bug

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Red Spider Mite Web

Leaves have rusty brown mottling and may fall.

Leaves lose luster and turn grayish green.

Mite damage occurs mostly during hot summer and on evergreen azaleas.

Lace bug damage appears in early to mid summer.

 

Spray with malathion, carbaryl or pyrethrin at first sign of attack.  Make sure you get leaf undersides.  Repeat 3 times at 10 day intervals.

For spider mites, spray with dicofol or other miticide.

To prevent infestation, spray leaves regularly with water or insecticidal soap solution.

ProblemSymptomsControl
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Borer		Older branches at center of shrub may have small holes.  Some branches may die.

Severe infestations result in tunnels on branches.

Spray with lindane or malathion twice in late spring, 2 weeks apart.

Check with your local Rhodo society for specific timing, which is critical for control.

Borers can be killed by inserting wire into their tunnels.
ProblemSymptomsControl
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Vine Weevil		Leaf edges have semi-circular notches.

Leaves may have poor color, indicating that weevil larvae are feeding on roots or main stem.
In late spring or early fall, spray at 10 day intervals with a systemic insecticide like methoxychlor or Diazinon, or apply 14% diazinon granules to soil surface.

Fungus Diseases

ProblemSymptomsControl
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Leaf Spot Fungus		Leaves have round, dark red or brown spots usually in late summer.Spray with zineb or other fungicide before spots appear in late spring.

Later treatments are not usually effective.  In a pinch you could apply a systemic fungicide weekly for the rest of the growing season.
ProblemSymptomsControl

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Petal Blight fungus

Tiny spots on undersides of petals enlarge and bleach out.

Flowers wilt.  Buds appear to blast.		Spray with Benomyl or other systemic fungicide every 5 days during bloom season.
ProblemSymptomsControl

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Wilt Fungus

Young shoots on single branch wilt and brown in midsummer, or entire shrub may wilt.

Diseased branches show brown stain under bark just below soil level.
Remove and destroy diseased branches.  
In severe cases destroy entire shrub.  To prevent disease, use soil drench such as Terrazole.

To prevent spread, take care not to splash spores from soil surface onto shrub.

Chlorosis

ProblemSymptomsControl

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Chlorosis 

Leave show yellow patches between veins or are flushed all over.

Leaves may wither.		Ensure soil is acidic and light with peat and composted bark.  Treat with chelated compounds like sequestered iron, or flowers of sulphur, and mulch with compost or well composted pine bark, kept evenly moist.

Drought

ProblemSymptomsControl

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Drought

Brown flower buds, drooping or wilting leaves.

The peat/bark soil required for Rhododendron species is particularly vulnerable to drying out.  Keep evenly moist by watering deeply.

Augment heavy soils or plant with rootball on the soil surface, and the soil-peat-bark mix mounded up over it.  Use plastic, metal or wood edging if required to retain soil.

Azaleas as Houseplants

ProblemSymptomsControl

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It's hard to keep them
looking like this.

Bud drop, leaf drop, browning, etc.

Don't even try to grow azaleas indoors unless you can maintain 60 degree temperatures with 40% or higher humidity and long periods of bright light, without much direct sun.  Also avoid hot or cold drafts.

If a gift azalea survives, put it outdoors for the summer in a part-shade location and keep evenly moist.  It may survive to bloom indoors a second year.  If you are in a frost free zone, plant outdoors with some winter protection.

Pruning and Deadheading Azaleas and Rhododendrons

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Deadheading

When the flowers are spent, snap off the green tendrils at their base where they join the center of the leaves.

Pruning

Every few years, when the shrub gets too leggy, prune just above a shoot with healthy leaves.

Pinching Back

Each year, after blooming, new tender green shoots will emerge.  When they are 2" long and have 6 or more leaves, pinch off the growing tip leaving 4 leaves.

 

Hardiest Rhododendrons and Azaleas to Grow

RhododendronsAzaleas

Album Elegans:  pale lilac fading to white, Zone 5

America:  dark red, zone 5

Boule de Neige:  clear white, zone 5

Catalode or County of York:  creamy white, zone 7 (fragrant)

Catawbiense Album:  wite with yellow spots, zone 5

Catawbiense Boursault:  mauve-lilac, zone 5

Chionoides:  clear white, zone 6

English Roseum:  pink, zone 5

E.S. Rand:  crimson red, zone 6

Katherine Dalton:  clear light pink, zone5 (fragrant)

Maximum Roseum:  clear pink, zone 5

Nova Zembla:  dark red, zone 5

Parsons Grandiflorum: pale lilac, zone 5

Purpurcum Elegans:  purple-blue, zone 5

Roseum Elegans:  mauve, zone 5

Roseum Pink:  clear pink, zone 6

Evergreen:

Gaiety:  bright pink, zone 7

Geisha:  striped, zone 7

Hino-Crimson:  bright crimson-red, zone 6 

Louise Gable:  salmon double, zone 6

Polaris:  white semi-double, zone 7

Red Progress:  bright red, zone 7

Rosebud:  pink, zone 7

Deciduous:

Gibraltar:  orange frilled, zone 6

Jolie Madame:  clear pink, zone 6 (fragrant)

Peachy Keen:  pink with red, zone 6

Pink William:  silvery pink, zone 6

Red Letter:  bright red, zone 6

Rufus:  deep red, zone 6

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