Question:
How can I control powdery mildew on my garden phlox?Answer:
Powdery mildew is a common disease of garden phlox (Phlox paniculata). The fungal disease produces a grayish white coating on the leaves. Infected leaves eventually turn yellow and then brown. Initial symptoms appear on the lower leaves with the disease progressing upward.
Powdery mildew is most commonly found on plants growing in shady areas and in crowded plantings with poor air circulation. Optimal conditions for powdery mildew are cool nights followed by warm days.
Cultural practices can reduce the severity of powdery mildew on garden phlox. The amount of disease inoculum can be reduced by cutting off and removing diseased plant debris in the fall. Plants growing in shady locations should be moved to a sunny site. In overcrowded plantings, improve air circulation by digging and dividing perennials.
While cultural practices are helpful, fungicides may be necessary to control powdery mildew on garden phlox. To be effective, fungicides should be applied at the first sign of the disease and repeated on a regular basis.
Selecting and planting powdery mildew-resistant varieties is one of the best ways to reduce issues with powdery mildew. The following cultivars possess good resistance to powdery mildew:
- ‘Jeana’ (lavender-pink flowers; 2024 Perennial Plant of the Year)
- ‘Glamour Girl’ (coral-pink flowers)
- 'Delta Snow’ (white flowers with purple centers)
- ‘Lavelle’ (white flowers with pale pink centers)
- ‘Robert Poore’ (violet-pink flowers)
- ‘Dick Weaver’ (magenta flowers)
- ‘David’ (white flowers; 2002 Perennial Plant of the Year)
- ‘Ditomdre’ (Coral Crème Drop™) (salmon-pink flowers, dark stems)
- ‘Shortwood’ (pink flowers)
- ‘Babyface’ (pink flowers with dark pink centers)
- 'Frosted Elegance' (white flowers with pink centers; variegated foliage)
- 'John Fanick' (light pink flowers with dark pink centers)
- 'Peppermint Twist' (flowers with pink and white stripes)
- 'Katherine' (lilac blue flowers with white star-shaped centers)
- 'Orange Perfection' (salmon-orange flowers, shorter than most cultivars)
*The resistance or susceptibility of garden phlox varieties to powdery mildew varies within the United States. A variety that possesses good resistance to powdery mildew in the Midwest may be susceptible to powdery mildew in other regions of the country.
Additional Resources
- A Comparative Study of Phlox paniculata Cultivars Chicago Botanic Gardens
- Phlox for Sun Mt. Cuba Center
Photo credits: David L. Clement, University of Maryland, Bugwood.org