As the weather finally takes a cooler turn, it’s time to be on the watch for downy mildew outbreaks.
Those in the San Diego area should particularly monitor their Red Apple ice plant (Aptenia cordifolia), which is a popular ground cover succulent that was devastated by downy mildew last year.
The downy mildew fungus thrives in damp, dark, cool conditions. It creates yellow splotches on the upper surface of leaves while on the underside a blue-white fluffy growth can be seen. If conditions are favorable, this disease can reproduce rapidly.
Red Apple ice plant is used along on slopes and hillside properties to help prevent soil erosion, but downy mildew leaves brown, decayed remains after it has hit.
Heaviland Landscape Management advises taking these preventive measures:
- Avoid using overhead irrigation during the evening, as combining moisture and dark conditions creates an ideal breeding ground for the fungus.
- Ensure plants receive enough light and airflow so leaves can dry faster after irrigation.
- Apply fungicide before downy mildew appears. Infected plants cannot be cured.
“A proactive approach is the best way to manage and prevent outbreak this winter,” said Bernie Buggs, branch manager for Heaviland Landscape Management. “Landscape managers should ensure proper growing conditions as suggested and apply preemptive fungicide applications now, as the weather cools.”
This disease should not be mistaken for powdery mildew, which also favors humid conditions but appears in more moderate temperatures.
Downy mildew is not an issue for landscapers in Northern states during the winter, as it cannot survive in the colder temperatures. The fungus only reaches Northern states in the spring by being blown in on air currents.