Knowledgebase
Waxleaf ligustrum disease vs. frost damage? #785002
Asked March 24, 2022, 2:20 PM EDT
Hello and thank you for taking time to read my question. I live in Southlake and have some Waxleaf Ligustrum shrubs that are about four years old in my front yard. I noticed yesterday that many of the leaves on the ligustrum shrubs have brown/yellow discoloration and white dots. Some of the discoloration is in a band like distribution on the leaves, and others have a central white or black dot with discoloration spreading around the dot. Multiple shrubs are affected in different locations. We had freezing weather approximately two weeks ago. I am at a loss as to whether this is frost damage or a disease...or both? Any help with this is much appreciated.
Tarrant County Texas
Expert Response
Additional photos of issue.
Diagnosis via photo is a dangerous thing, but I'll give it my best shot. I think you may have more than one problem going on.
First, I think you suffered some freeze damage. In particular the areas on leaves that look white and completely necrotic could be due to freezing. You can't do anything about freeze damage at this point except to wait for the plant to drop the damaged leaves and replace them with new growth.
Second, there are spots that look more like a fungal leaf spot. I'm thinking of the dark rings surrounding dying leaf tissue. Many diseases that affect ligustrum live in the soil on dead leaves. The most important thing to do is to keep the ground below your plants clean and free of dropped leaves. Rake well and dispose of removed leaves in the trash in a sealed plastic bag. Fungicides aren't very effective but those containing myclobutanil and azoxystrobin seem to work the best. If you use one, spray both the plant and the ground below. Fungicides will not cure affected leaves but they can reduce the further spread of the disease. Read the labels and select a product specified for use on leaf spot infections of ornamentals.
Third, I see a lot of small white spots on stems and twigs. Look at the plants closely to see if you have scale insects. Scale insects don't move much and can look like a small white fuzzy patch or they can have a smooth shell for protection. Scale is hard to treat because the white fuzz or the hard shell protects them from treatments you apply. Try a horticultural oil or insecticidal soap to reduce scale populations if you determine that you have scale.
Fourth, your plants are very dense and shrubby. They could benefit from some careful thinning to improve air circulation and faster drying after rain or dew. If you trim them in this way, dispose of all the cuttings in plastic bags in the trash.
Finally, water the ground around the plants, not the leaves. Wet leaves promote leaf spot diseases. If your irrigation system uses above ground sprayers, then water in the early morning near sunrise so the plants will quickly dry and reduce infections.
I hope this helps. Good luck.
Rick Coke
