Azalea Problems: Azalea Diseases & Pests

Azalea Problems: Azalea Diseases & Pests

Azaleas are one of the most popular spring-flowering shrubs seen in landscapes. While these attractive plants are generally hardy and problem free, they are occasionally bothered by pests and diseases.

Azalea Plant Pest Control

Some of the more common azalea plant pests include the following:

Azalea Bark Scale – This azalea plant pest occurs most often in the eastern United States. Affected shrubs may be covered with sooty mold or appear as white, cottony masses within the forks of branches. These branches should be removed and destroyed. Treatment with horticultural oil can help.

Azalea Caterpillars – These alzalea pests are reddish to brownish black with white and yellow stripes. Feeding in groups, azalea caterpillars can quickly defoliate shrubs. Control is often accomplished through handpicking, as they pose no threat to humans. Bt products are also effective.

Azalea Lace Bugs – These are one of the most common threats to azalea shrubs. Affected plants may have yellow to whitish-looking foliage with black bugs located in numbers on the underside of leaves. Insecticidal soap is usually effective in controlling lace bugs in late spring or fall.

Azalea Leafminers – This azalea plant pest generally “mines” between the upper and lower surfaces of leaves causing brown blisters or yellowing on the leaves. Affected leaves may also curl up and drop. Removal of affected plants may be necessary.

Stunt Nematode – These azalea pests attack the feeder roots and cause azalea plants to become stunted and yellow. Plants with heavy infestations eventually die. While there is currently nothing available to control nematodes on azaleas, with proper fertility and watering practices, the plants are better able to tolerate attacks.

Whiteflies – These pests usually occur in groups on the undersides of leaves, which turn yellow or die. Whiteflies do not respond well to treatment; however, neem oil may reduce populations.

Azalea Diseases

The most common azalea diseases affecting these shrubs include:

Azalea Gall – This azalea disease commonly occurs in early spring on new leaf growth. The leaves become curled, fleshy, and pale green to white. Affected leaves eventually turn brown and should be removed and destroyed.

Petal Blight – This fungus only affects flowers and appears as pale or whitish spots on colored petals or rust-colored spots on white petals. These spots quickly enlarge, becoming soft and watery. Apply a fungicide to buds as they begin to turn color.

Powdery Mildew – This azalea disease appears as white powdery growth on the leaves and occurs most often during fall. Diseased leaves may drop prematurely. May require fungicide spray.

Rust – Rust is a fungal disease that causes reddish to orange spore masses on infected leaves, as well as galls or cankers on bark, which may occasionally kill the entire plant. Prune and dispose of infected leaves and shoots immediately.

Twig Blight – Twig blight may cause wilting and defoliation on one or more branches with a reddish-brown discoloration under the bark. Control with pruning and disposal of diseased branches, making cuts a few inches below discoloration.

Environmental Azalea Problems

Sometimes there are environmental factors that are associated with azalea problems. For instance, frost damage can cause all parts of the shrub to wilt, turn brown or black, and die. New growth is especially susceptible in early spring. To prevent frost damage, do not grow tender species in cold climates, and cover shrubs with sheets or burlap anytime frost is expected.

Nutrient deficiencies are another common factor with azaleas. Plants may exhibit discoloration with fewer or undersized foliage and flowers. Nitrogen and iron are the most commonly seen deficiencies in azaleas.

Inappropriate watering can cause foliage to wilt, discolor, and drop. On average, established azaleas require an inch of rainfall or irrigation per week during their active growing season.

Too much or too little light can also damage these plants. Leaf scorch, which is caused from too much sun, may appear as yellow or brown spots on foliage.


Root Weevils

Root weevils are the primary insect enemies of deciduous azaleas. Adult weevils damage the appearance of the plant by notching the leaves at night however, sticky insect tape wrapped around the lower part of the trunk prevents the pests from climbing up to the leaves. The root weevil larvae cause more serious damage as the pests girdle the roots of the plant. Parasitic nematodes, which prey on the larvae but don't harm the plant, are often an effective means of control. Some pesticides are helpful, including pyrethrin, a natural insecticide produced by pyrethrin daisies.


GARDENING AUSTRALIA

SERIES 16 | Episode 13

Over the grey months of winter look out for the many gardens filled with azaleas, and their vibrantly coloured pink, mauve, orange and golden yellow flowers.

Azaleas are in the rhododendron family Ericaceae. These plants originate from Japan, China and Korea. There are three main types of azalea - the indica hybrids, the karume hybrids and the mollis hybrids. The indicas spot flower from autumn through winter, with their main flush in spring.

Azaleas grow well in a range of climates from Brisbane to Perth, and further south to Melbourne. They thrive in a slightly acidic soil with good drainage.

Azaleas look great planted en masse in a garden bed. But remember to use plenty of compost - it acts like blotting paper around the roots, and keeps them moist but not over wet. Use a mulch, even chopped up leaves, on the soil surface.

If there is no room in the garden then azaleas also do well in pots. When potting into a pot make sure there is a drainage hole at the bottom, and use a good quality potting mix.

Just tickle the roots and backfill with the mix. A good tip is to leave a gap between the top of the potting mix and the pot so the water doesn't overflow. Liquid fertilise and keep moist during the growth time over spring and summer.

Unfortunately azaleas have a reputation of being prone to pests and diseases. For example, look out for azalea lace bug on the leaves. A sign of this sap- sucking bug is brown and silvery mottled leaves. To control this it's best to spray in spring, at the start of the growth season. Jane suggests seeking advice from your local nursery about possible sprays because some are poisonous. The other method of control is to prune the damaged branches. Prune after flowering for plenty of new growth.

During a wet winter you might find some of the flowers on the indicas become mushy and brown. This is called azalea petal blight. Spray this with a fungicide, or simply remove the flowers and dispose of them.

Azaleas can also grow long, rather spindly looking stems so prune these off after flowering to ensure a compact bush.

Recently much work has been done hybridizing azaleas, so they are more tolerant of a wider range of soils and climates, and there are always new varieties and colours on the market to look out for.


Azalea problems

I hope someone can identify the white powdery substance on this rather old (maybe 30 years or so) azalea. Also the color of the bark is greyish, in some cases almost black.

Any information as to what this is and even better, what (if anything) can be done about it. (other azaleas nearby all look normal)

Looks like Mealy Bug to me
Mealy bugs are white, soft-bodied insects that suck plant juices, sometimes people mistake a mealy bug infestation for a fungus.
See sample photo
http://www.hibiscus.org.au/bugs/mealy.jpg

You can treat it organically or chemically depends on your preference

organic:
Prune and discard infected portions of the plant
and or use insecticidal soap. Spray the plant thoroughly every 5 day for 4 weeks to cover all stages of growth.
For smaller infestations, dab the insects with a cotton swab dipped in rubbing alcohol. Repeat this procedure every week until the bugs are gone.

chemical: imunox or sevin spray both work

It would be good to take care of it quicly so they don't spread to your other azelas
Good luck

Thanks for the advice. I will go out to Home Depot tomorrow morning and see what they have for mealy bugs.


Dieback

Botryosphaeria rot and canker (Botryosphaeria spp.)
Elizabeth Bush, Virginia Polytechnic Institute and State University, Bugwood.org

Dieback is an important disease of hybrid rhododendrons in the landscape and is caused by the fungus Botryosphaeria dothidea. Azaleas with similar symptoms are more likely to be infected by the fungus Phomopsis species. Typically, dying branches (stem dieback) begin to appear on an otherwise healthy plant. The leaves die and can remain attached to the plant until late summer.

Usually a single branch on an established plant is affected. Scraping away the bark with a knife reveals a reddish-brown discoloration under the bark on dying branches of rhododendron. On azaleas the discolored wood under the bark appears chocolate brown.

Prevention & Treatment: Dieback is difficult to control on rhododendrons and azaleas in the landscape. The azalea varieties that are the least susceptible include: ‘Delaware Valley White,’ ‘Hershey Red,’ ‘Pink Gumpo’ and ‘Snow.’ The following rhododendron varieties are considered resistant: ‘Boursalt,’ ‘Chionoides White,’ ‘Cunningham’s White,’ ‘English Roseum,’ ‘Le Barr’s Red,’ ‘Roseum Two’ and ‘Wissahickon.’

Reduce stress to the plants by planting in partial shade and watering during dry periods. Drought stress and freeze injury may predispose azaleas to infection. Avoid wounding the plant. Prune infected branches well below all discolored wood and dispose of dead plant material. Clean pruning tools between cuts with a dilute solution of household bleach (1 part bleach to 9 parts water) or 70% rubbing alcohol. For azaleas, fungicide sprays containing either thiophanate-methyl or mancozeb can be used. For rhododendrons apply a product containing a copper-based fungicide or chlorothalonil. See Table 1 for examples of products. Apply all chemicals according to directions on the label.


Root Weevils

Root weevils are one of the worst insect pests that trouble azaleas. This pest is found in nearly all parts of the world and attacks over 100 different species in addition to azaleas. Black Vine weevils are the most common of the species. This insect ranges in size from one-quarter to one-half inch and ranges in color from gray to black. If this bug is pestering your azalea, you will notice notches or spots that look like the edges of the leaves have been nibbled. Although this pest can make your azalea look damaged and unsightly, it is not usually hazardous to your plant’s health. Prevent root weevils by pruning off lower leaves to prevent access to the plant.


Watch the video: Lacebug Damage and Treatment on Azalea