Azalea Pest – Azalea Bark Scale


By: Jackie Rhoades

Help! My azalea’s turning black! You’ve been attacked by the scourge of the azalea. You’ve been invaded by the azalea bark scale.

Identifying Azalea Bark Scale

Blackened branches, covered by a sticky soot and white, cottony fluffs in the crotches of the lower branches are all symptoms of one of the most dreaded of azalea diseases. Black branches are the result of mold growing on the honeydew excreted by this azalea pest.

Azalea bark scale looks like, and is often mistaken for, mealybugs. The female is covered with waxy threads that harden into a protective scale as her egg sac forms. The azalea bark scale is tiny, but her effect, as seen on your azaleas turning black, is terrible.

As this azalea pest feeds, she secretes a honeydew on the azalea. Blackened branches, made so by honeydew and mold, eventually sicken and die, as does the female when her egg sac is full.

Treating Azalea Bark Scale

Eggs are laid in late April and a new batch of this azalea pest hatches in about three weeks. This is the time when treatment is most effective. Mature azalea bark scale wear shields. The nymphs haven’t had time to develop them. The time to attack your azalea blackened branches is while the azalea bark scale are nymphs.

To fight the azalea diseases black branches, the most effective weapons in your arsenal are horticultural oil or dormant oil and insecticidal soap. Cut away any of your azalea blackened branches that are dead or severely damaged and wipe away as much of the soot as you can with gloved hands. Spray the plant thoroughly, including the underside of the leaves. Continue spraying regularly through September and begin again in early spring.

With the proper strategy, you can win this battle against the most aggressive of azalea diseases. Blackened branches be gone! You’re at war with a tiny insect known as the azalea bark scale. Good luck and good hunting!

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Black Spots on Azalea Leaves

Black spots on the foliage of the azalea shrub often indicates a pest infestation. Both the azalea whitefly (Pealius azaleae) and the azalea lace wing (Stephanitis pyrioides) feed on the sap of the shrub by piercing its foliage with their sharp mouths and sucking the nutrients. The azalea whitefly prefers the snow azalea (Azalea ledifolia alba) but does occur on other varieties.


Identification

Azalea bark scale insects (Eriococcus azaleae Comstock), discovered in the United States in 1881, have earned a reputation as significant azalea pests. The white mounds congregating on azalea limbs are adult females and their egg sacs, shielded beneath a dense, insecticide-resistant covering of waxy white threads. Once shielded, the reddish insects remain where they are until death. Their larvae, or crawlers, hatch beneath the covering that looks like raised white spots and emerge to settle and feed in bark crevices.


Caring for a Burned Azalea

Azaleas are closely related to rhododendrons, which also belong to the genus Rhododendron. Some rhododendrons and azaleas are native to North America, while others that are used for landscaping in the U.S. are descendants of species native to Asia, according to Clemson Cooperative Extension. Native plants tend to be more cold hardy than those imported from other areas of the world, as they are adapted to the local climate.

Regardless of whether the plant is dehydrated or not well suited to your area, pruning a burned azalea shrub to remove damaged branches can improve its chances of survival. Remove damaged azalea branches by cutting them close to ground level with clean, sanitized pruners. Before pruning, check to see if the damage to branches is deep or surface level by scraping back some bark first if you see green growth after removing the bark, this means that the branch may revive in time. Wait and watch for a few weeks before removing any branches with the potential for recovery.


Are these indoor or outdoor azaleas? (Some azaleas are sold as decorative seasonal houseplants as they are forced into early bloom.) Recommended treatment may depend on their location.

The insect in the picture insect looks like a mealybug, though Azalea Bark Scale can have a similar appearance. The former would be more likely for an indoor plant the latter more likely for an outdoor plant.
https://extension.umd.edu/hgic/topics/soft-scales-trees-and-shrubs
https://extension.umd.edu/hgic/topics/mealybugs-houseplants

How extensive is the insect infestation? Black deposits could point to two causes - either sooty mold that grows on wastes from the insect sap-sucking or residue from an older outbreak of lace bug. Residue from lace bugs appears as tar-like spots underneath the leaf, and this is where they lay their eggs. https://extension.umd.edu/hgic/topics/lace-bugs-trees-shubs An example of sooty mold can be seen in the first of the two links above. In and of itself, it is harmless except when so extensive that it keeps the plant from photosynthesizing. It will disappear on its own after the pest outbreak is under control.

If Azalea Bark Scale, the vulnerable stage (called "crawlers") tend to appear around late May to early June (on average, in our area) and again in mid-July. Horticultural oils up to about a 1% concentration should work check the product label for how to use (some are sold ready-to-spray, others concentrated) and be sure to coat as much of the plant as you can - most importantly, the twigs and the undersides of the leaves. Frequency of application depends on which pest is involved and the exact product used, but in general, 2-3 applications each about 1-2 weeks apart should knock down the population. The product label will advise you on how often to re-apply.

Scale tend not to move once they mature past the first hatchling ("crawler") stage. While mealybugs are a type of scale (and move around often), they are an exception. Yes, it is possible that they are maturing juveniles that were present all along that are just now becoming noticeable. Dormant oil can be sprayed on overwintering scale, but using it this is late in the season in warmer temperatures risks injuring the azalea itself. Horticultural oil is less concentrated and is best for warm-weather use (but below 85 degrees).

Beneficial predators can detect and help manage pest outbreaks, but can be harmed by direct spraying if they arrive after sprays have dried, however, there is little risk to them. Therefore, it's best to try spraying during the first wave of crawlers in a few weeks from now, to knock down the population and allow predators to find them and finish them off this summer. You can use double-sided tape (or single-sided tape wrapped sticky-side out) around some of the azalea stems to help monitor when the crawlers are present. They are similar to mites in size (small, but visible, though may need a magnifying glass) and will get stuck to the tape as they attempt to crawl over it.


First off, when talking about Encore Azaleas, at 6, they are on the edge of hardiness zones in Maryland. Take a look at this link to a map of your county: http://www.plantmaps.com/hardiness-zones-for-montgomery-county-maryland to see where you are.
The issue is likely a combination of factors, including normal leaf drop, winter damage and pests.
While azaleas can have some problems, which we will cover below, the absence of flowers is unusual. We would like to see a couple of photos of the entire plants, and know more about their placement in the landscape. This can be attached right to this reply.

Are you pruning or trimming these shrubs? It's possible you are inadvertantly pruning off flowering shoots.
That said, we do see some signs of what we think is probably lacebug damage on some of the leaves. Look on the underside of the leaf for black fecal dots and maybe even some of the lacy-winged bugs themselves. It is more likely to occur on regular azaleas in full sun.
Take a look at our IPM Azaleas and Rhododendron publication at this link and compare with what you are seeing: https://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG51_IPM_.

For your Rudbeckia, the first photo looks like a leaf spot disease which can be very damaging, and the second looks like it could be cold damage.
More on the leaf spot:
Septoria on rudbeckia: There are a number of diseases that affect the leaves of the popular black-eyed Susans. One common disease is septoria, which causes dark brown leaf spots. Try to avoid wetting the leaves . For a description of common rudbeckia diseases see: http://extension.psu.edu/pests/plant-diseases/all-fact-sheets/rudbeckia-diseases(link is external).
It can be difficult to control, leading to the removal of beds of plants.

Thank you very much for your response. I went out again to check the azaleas and sure enough I saw bugs on them Tiny white ones ones with black lines. My daughter who has a degree in biology got her entomology book to see what they were. The lace bug. There are many more on the ones in the sun than in the shade even if they both haven't bloomed in 2 years. Now the question is, what do I do?

I hope you don't mind me sending you picture of the leaves in my back eyed susans. I checked your page, but it got rather confusing and I'm getting pretty scared. Thanks again!

I do have a quick question about something else my husband keeps pounding on me to ask you. The branches on our Nelly Stevens Hollies are turning black and leaves are dying. We were told it was black ash borer and need to spray it with oil. We were hoping you could tell us what type of people do this type of work.

Thank you again for all your help which has been fantastic. Glad someone just
told us about you.!

Thank you very much for your response. I went out again to check the azaleas and sure enough I saw bugs on them Tiny white ones ones with black lines. My daughter who has a degree in biology got her entomology book to see what they were. The lace bug. There are many more on the ones in the sun than in the shade even if they both haven't bloomed in 2 years. Now the question is, what do I do?

I hope you don't mind me sending you picture of the leaves in my back eyed susans. I checked your page, but it got rather confusing and I'm getting pretty scared. Thanks again!

I do have a quick question about something else my husband keeps pounding on me to ask you. The branches on our Nelly Stevens Hollies are turning black and leaves are dying. We were told it was black ash borer and need to spray it with oil. We were hoping you could tell us what type of people do this type of work.

Thank you again for all your help which has been fantastic. Glad someone just
told us about you.!

Lace bugs will be a persistent problem on azaleas located in full sun. You may want to consider transplanting them to a location that gets part shade. Here is a link to our fact sheet on azalea lace bugs and several options for controlling them:
https://extension.umd.edu/sites/extension.umd.edu/files/_images/programs/hgic/Publications/HG95%20La.

The symptoms on your Rudbeckia are consistent with Septoria Leaf Spot. This is caused by the fungus. It overwinters on infected plant residue and spores are produced in late spring, which is when it spreads. The first symptoms are small angular lesions on the lower leaves. Leaf lesions eventually develop on upper leaves. The spores of the fungus are dispersed by splashing water and can cause secondary lesions throughout the growing season.

Begin control by removing and destroying infected plant material from the previous season. Prevent crowding and promote good air circulation to keep leaf surfaces dry by properly spacing plants and removing volunteers and weeds. Avoid overhead watering. It can be difficult to control and sometimes requires removing an entire bed of plants.

The symptom you describe on your Nellie Stevens Holly sounds like it might be sooty mold. These hollies are susceptible to scale insects (Cottony Camellia Taxus Scale) which produce a honeydew secretion and then a black mold grows on the honeydew. The scale tends to accumulate on the undersides of foliage. Here is some information about this scale and how to control it: https://extension.umd.edu/hgic/cottony-camellia-scale-shrubs

Thank you for all your information. I'll put the sun azaleas somewhere in partial shade (even though the ones we have in the partial shade, mostly shade, have the same problem) and hope they eventually will bloom.

Will be calling a tree service to spray horticultural soap.

*Just one question about my black eyed susans. They are in the front of my border in groupings and in another bed and all are affected. They're pretty close together now through self seeding. Should I take them all out and replace them with new ones or just take some out to reduce the crowding? I read that some people say it's nothing just ugly or it's overcrowded and just take out dome so they won't be crowded. So now I'm confused as to what to do.

Thank you for all your information. I'll put the sun azaleas somewhere in partial shade (even though the ones we have in the partial shade, mostly shade, have the same problem) and hope they eventually will bloom.

Will be calling a tree service to spray horticultural soap.

*Just one question about my black eyed susans. They are in the front of my border in groupings and in another bed and all are affected. They're pretty close together now through self seeding. Should I take them all out and replace them with new ones or just take some out to reduce the crowding? I read that some people say it's nothing just ugly or it's overcrowded and just take out dome so they won't be crowded. So now I'm confused as to what to do.

Unfortunately, this can become a problem that is more than just ugly. For some stands (even ones that have been thinned) there is just so much disease that the plants end up crispy and brown.
It is your decision if they get to a point that they have lost their attractiveness and you want to pull them. (I personally try to save everything, but this is one case where I gave up and got rid of it all).
There may be disease resistant varieties that would do better for you.


How do you treat azalea bark scale?

If so, you have a fungus called powdery mildew. Your local garden center will have a general purpose fungicide that will work for well on powdery mildew. If the white on the leaves is more of a lacy pattern on the leaf that can not be wiped away, your azalea has been attacked by an insect called lace bug.

Also, how is Azalea fungus treated? Prevention & Treatment: Remove fallen leaves. Keep leaves dry when watering plants. Fungicide sprays during periods of high humidity will prevent serious foliage damage. Fungicide sprays recommended for azaleas include copper hydroxide, copper-based fungicides, thiophanate-methyl or chlorothalonil.

Similarly, what do you spray azaleas with?

But one application of a systemic insecticide containing imidacloprid or acetamiprid in late to mid spring will kill the later emerging nymphs as well as the earlier ones before they reach adulthood. An organic control is horticultural soap.

Why is my azalea turning black?

Black branches are the result of mold growing on the honeydew excreted by this azalea pest. Azalea bark scale looks like, and is often mistaken for mealybugs. The azalea bark scale is tiny, but her effect, as seen on your azaleas turning black, is terrible.


Watch the video: Azalea Pests


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