Powdery Mildew, Blumeria graminis, is a common and relatively recognizable disease affecting a wide range of host trees. This disease infects plants during times of high humidity, most often in the late spring through summer. Symptoms are most commonly found on the upper side of leaves, but can also infect stems, buds, flowers, and fruit. Powdery mildew can be prevented easily, but proactive action is required, most fungicide treatments do little benefit when applied after symptoms have formed. This disease occurs across the entire United States.
Treatment Strategy
Often times the use of cultural controls can keep symptoms at bay; however, during especially wet springs a spray applied fungicide can provide additional control. For severe infections preventative fungicide applications can be helpful in controlling symptoms. Although the disease is relatively easy to control, proper timing, before symptoms appear, is crucial to getting good control. Products such as Myclotect™ offer a locally systemic protection, and are therefore very effective when applied as leaves. Follow up applications can be applied at 7-14 day intervals through mid-June to maintain protection.
Other Treatment Practices
- Cultural controls including:
- Spacing plants appropriately
- Removing dead plant material
- Pruning for air flow
- Not watering from overhead.
- Avoid the use of high nitrogen fertilizers as over fertilization can also cause problems by increasing foliage growth.
- Cambistat can be used to increase plant resistance to diseases
Foliar Spray Using Myclotect
Foliar Spray Using Pegasus 6L
Foliar Spray Using Talaris 4.5F
Expected Results
Fungal diseases will always be present. Suppression of the disease is to be expected, not eradication.
Signs of Damage
- Reduced plant vigor throughout the year
- Early leaf drop of infected leaves
- Chlorotic (yellowing) patches surrounding lesions and grey mycelia growths
- Infection is generally strongest on foliage closest to the soil
- White powdery mycelial and conidial growth on leaves, stems, buds, or fruits are visible during the growing season
- Dark grey or black fruiting bodies appear intermixed with the white mycelial growth as symptoms progress
Photo: University of Georgia Plant Pathology Archive
University of Georgia, Bugwood.org
Photo: University of Georgia Plant Pathology Archive
University of Georgia, Bugwood.org
Photo: Clemson University
USDA Cooperative Extension Slide Series Bugwood.org
Trees At Risk
Almost any landscape plant.
Biology
- During high humidity conditions, host plants become infected.
- Spores are moved by rain, wind, or insects.
- Powdery mildew overwinters as mycelia or spores in leaf litter under plants.
References
Colorado State University
https://extension.colostate.edu/topic-areas/yard-garden/powdery-mildews-2-902/
University of California Davis
http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7493.html
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
