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Fungal diseases on landscape ornamentals

Temperatures are fluctuating between cool and warm, and there is moisture in the air. These are conditions that are conducive to some plant diseases. In the last 2 weeks, I have been seeing an increase in both POWDERY MILDEW on crape myrtles and BLACK SPOT on roses. These are the common name of disease that actually describes what we see on the plant. Powdery mildew, as it’s name imply have a powdery appearance on the infected leaves. You may have noticed that not all crape myrtles are affected by this fungal pathogen. In my own yard, new growth the variety “ Country Red” and “Tuscarora” was severely infected while “Townsend” which was adjacent to the “Country Red” showed no symptoms at all. This is the reason that choosing a resistant variety is a cost- and labor-efficient method of managing this disease. Similarly, black spot on roses that is caused by a fungus, attack different varieties with varying degrees of severity. “Knock-out” rose (an designated EarthKind rose) has good resistance to this pathogen. However, varieties such as “Charisma” and “Peace” are highly susceptible to black spot disease. For more information of powdery mildew on crape myrtle, check out this factsheet . To learn more about black spot on rose, click here to download the factsheet. You can also find a general factsheet on rose disease titled “Common Rose Disease” at our AgriLife Bookstore.