Richard C. Bogren, Huffstickler, Kyle, Gill, Daniel J., Owings, Allen D.
Azaleas either do great in Louisiana, or they do poorly. The LSU AgCenter regularly receives questions on azalea issues this time of year, but more inquiries than usual have come this spring.
Many azalea problems this summer suggest drying foliage with partial to whole-canopy dieback. A number of reasons may be responsible for this. The weather from April through early June was dry enough for drought-stress symptoms to be appearing on azaleas that weren’t adequately watered.
On the other hand, over-irrigation is common in commercial and residential landscapes. If azaleas were over-watered in an effort to counteract drought conditions, those plants could be suffering from fungal organisms in the soil that attack and damage or kill the roots. Dead roots cannot absorb water, so when the upper part of the plant is deprived of the water it needs, it withers and dies.
This can often be distinguished from drought stress because it generally occurs sectionally. That is, a section of a plant will wilt and die (because it’s connected to roots that have been killed) while other sections (connected to roots that are still functioning) remain green. If lack of water in the soil is the problem, the entire plant wilts uniformly, but some portions of the canopy can show dieback faster than others.
The LSU AgCenter earlier reported cold damage on azaleas this year. Cold can cause internal damage that affects the plant's circulatory system. In other words, it interferes with the plant's ability to move water through the branches and into the leaves. Although it occurs in winter, branch death often doesn’t occur until warm weather arrives. Cold-damaged azaleas will show numerous splits and cracks in the bark and even peeling bark. These symptoms are often sectional as well, with some parts staying green and some dying.
Finally, azaleas may suffer from fungal infections of the branches themselves. These spots of infection cause cankers. The cankers block the flow of water to the branch beyond where they occur, and that branch withers and dies. This disease is called azalea dieback.
These are some possible answers to current azalea problems we are seeing.
Leaf gall was also present this spring. This is a fungal issue that creates unsightly malformation of azalea flowers and foliage. This has currently dissipated, so control is not currently warranted.
In addition to these problems, azalea lace bugs were very active this spring. If you see them, control them now in order to reduce the late summer/early fall populations. Systemic insecticides work well. You can also spray with horticultural/summer oil products. Stressed azaleas have more lace bugs than nonstressed azaleas, and azaleas in full sun have more lace bugs than azaleas in shady areas.
We hope this information will help with your azalea problems as we go through summer.
Visit LaHouse in Baton Rouge to see sustainable landscape practices in action. The home and landscape resource center is near the intersection of Burbank Drive and Nicholson Drive (Louisiana Highway 30) in Baton Rouge, across the street from the LSU baseball stadium. For more information, go to www.lsuagcenter.com/lahouse or www.lsuagcenter.com/lyn.