Tag: azaleas

An Introduction to NCSU Plant Disease and Insect Clinic

On By durhammastergardenersIn Common questions, Gardening information

by Andrea Laine, EMGV

You know you’re a serious gardener when you get excited about preparing a sample for the NCSU Plant Disease and Insect Clinic. I just wish I had engaged this problem-solving staff sooner and I hope you will learn from my experience.

Over the last three or four years, the mature evergreen azaleas in my landscape – of which there were many – began to succumb to a sudden dieback. Where there was once dark green glossy leaves and abundant flowering, seemingly overnight a swath of vertical branches would turn brown and die. I was alarmed, but knew not what to do. So, I did next to nothing: I trimmed out the crispy parts and hoped for the best.

I am ashamed to admit this experience was after my master gardener training. In training we certainly learned about the services provided by the Plant Disease and Insect Clinic, but either I didn’t think my plant problem was important enough to bother someone at NC State, or I was too lazy to prepare a sample. Probably a little of both.

The photo on the left was taken in 2013. The one on the right was taken summer 2019. It’s heartbreaking to see how robust the azaleas once were and are no more. Photos by A. Laine.

Inspired to act

Fast forward to this summer when two things happened that inspired me to act. First, the mysterious dieback attacked a stand of azaleas that are a key structural element in the design of my landscape (see photos above). And secondly, I noticed the exact symptoms on a few azaleas in a Durham neighborhood far from my own. The problem no longer belonged just to me; I resolved to seek a diagnosis on behalf of all of us.

My first step was to collect a soil sample from the vicinity of the azalea with the most recent dieback. The results showed that the soil pH was too high – 6.2 – where azaleas prefer a number between 4.7 and 5.3. Phosphorus was high and potassium was a little low. While all that is not a great situation for these acid-loving plants, it did not explain the sudden dieback. I needed to delve deeper.

I decided to access the NCSU Plant Disease and Insect Clinic. (You’ll find a direct link to it on the right side of this blog’s homepage as well as in the list of resources below.) I dug up a smaller azalea that had browned out a year or so earlier, left a good bit of the roots and soil intact and plunked it into a double plastic bag. Back indoors, I downloaded a submission form from the Clinic’s website, filled it out to the best of my ability and brought it and the sample to the master gardener office where I enlisted the help of our County Ag Agent Dr. Ashley Troth. Ashley submitted the sample on my behalf and we included digital images of the affected plants in my landscape. The more information a client can provide, the better will be the diagnosis and recommendations.

I had decided to remove these small, scraggly azaleas from the landscape anyway. So, I used half of one as my sample to the Plant Disease and Insect Clinic. Photo by A. Laine.

A diagnosis

A week later the diagnosis was in:  Symptoms are typical of Phomopsis dieback, a fungus disease. “The disease can be very serious if the fungus moves into larger branches and the base of the plant. This dieback was found down into the base of the plant submitted,” wrote Shawn Butler, an ornamentals diagnostician. “Presence of this disease,” he continued,  “often is an indicator of stressed or injured plants. Photos show that there is probably a problem in the root zones of these plants.  No root rot pathogens were isolated from these roots.  If the plants have been water-stressed in the past, then that might be the primary problem.” 

He also sent a root sample out to check for presence of damaging nematode populations. Some parasitic nematodes were found but populations were not high enough to cause damage.

A new pledge

I will take away at least two lessons from this experience (and I hope you do, too). The first is to seek help sooner, and the second is to not ignore long-established shrubbery. (These azaleas were planted at least 20 years ago.) The plants I inherited with my landscape deserve tender-loving-care equal to that which I provide to the plants I personally select for the landscape. 

Yet another azalea is affected. Removing it would leave a hole in the bush to the right as they have grown together over the decades. Photo by A. Laine.

Resources & Further Reading

How to submit a sample to the clinic: https://projects.ncsu.edu/cals/plantpath/extension/clinic/submit-sample.html

Meet the staff
https://projects.ncsu.edu/cals/plantpath/extension/clinic/about.html

Fees for the Clinic’s diagnostic services: https://projects.ncsu.edu/cals/plantpath/extension/clinic/services.html

Azalea care – a factsheet from Clemson University
https://hgic.clemson.edu/factsheet/azalea-care/

A comment about old azaleas from Louisiana State University
https://www.lsuagcenter.com/portals/blogs/southerngarden/problems-with-old-azaleas

Azalea Lace Bugs

On By durhammastergardenersIn Gardening information

Azaleas are in bloom right now, but you may also have noticed leaves that look like these:

azalea_lace_bug06

The azaleas in this photo from James L. Castner, University of Florida, have healthy new growth as well as previous damage from lace bugs. Lace bugs (Stephanitis pyrioides) are a common pest of azaleas here in NC. Nymphs and adults feed on the chlorophyll-containing tissues of azalea leaves, which gives the leaves a pale, spotted appearance. While this is mainly a cosmetic problem, if the infestation is great enough it can lead to early leaf drop and increased susceptibility to dieback diseases.

The adults and nymphs are tiny and can be found on the undersides of leaves, along with their waste and eggs. Nymphs have black markings and are spiny, while adults are cream colored with lacy wings. Lace bugs overwinter as eggs and may have 2-4 cycles per year.

azalea_lace_bug09 azalea_lace_bug01

(Photos: James L. Castner, University of Florida)

The first generation of lace bugs are usually active in April and May here in NC. Planting resistant cultivars of azalea and providing proper growing conditions will reduce damage. There are several beneficial insects that feed on lace bugs, including lacewings, assassin bugs, and spiders. If you have an infestation that is causing unacceptable aesthetic damage, Clemson University suggests the following control measures:

Insecticidal soaps may give some control of young lace bugs, and complete coverage of all leaf surfaces is essential. For adult lace bugs, recommended spray insecticides include bifenthrin, lambda cyhalothrin, malathion, carbaryl, and cyfluthrin. These insecticides are contact insecticides, and sprays need to be directed onto the lower surface of the foliage to be effective. Azaleas should be sprayed when the first lace bugs appear. A second application in seven to ten days may be needed to control newly hatched lace bugs. Good control of the first generation in March to May will greatly reduce problems later in the season. Control of second (July to August) and later generations (September to October) may be necessary. 

Systemic insecticides are no longer recommended due to the danger of harm to bees.

As with all pesticides, read and follow label instructions. Additional information, including pesticide information, can be found here. Please keep in mind that insecticides also harm beneficial insects, so they should be used with caution and only when necessary.

-Ann Barnes

More information: http://entomology.ifas.ufl.edu/creatures/orn/shrubs/azalea_lace_bug.htm

http://www.clemson.edu/extension/hgic/pests/plant_pests/shrubs/hgic2051.html