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Powdery Mildew Diagnostic Guide

Family Erysiphaceae

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 spring. 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.

Almost any landscape plant. The most common plants affected include lilac, dogwoods, roses, crape myrtles and crabapples.

Crab Apple

Crepe Myrtle

Dogwood

Rose

Signs of Damage

  • Reduced plant vigor throughout the year.
  • Early leaf drop of infected leaves.
  • Yellowing patches surrounding lesions and grey mycelia growths.
  • Infection is generally strongest on foliage closest to the soil.
Powdery Mildew Signs

Clemson University – USDA Cooperative Extension Slide Series Bugwood.org

Physical Appearance

  • 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.
Powdery Mildew Signs

University of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org

Powdery Mildew Signs

University of Georgia Plant Pathology Archive, University of Georgia, Bugwood.org

Treatment Strategy

Powdery mildew likes hot weather and high relative humidity. Oftentimes spacing plants appropriately, removing dead plant material, pruning for air flow, and not watering from overhead 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 of applications before symptoms appear is crucial to getting good control. Products such as Myclotect™ and Cleary 3336™ offer a locally systemic protection, and are therefore very effective when applied as leaves emerge in the spring. Follow-up applications can be applied at 7-14 day intervals through mid-June to maintain protection.

†Use of a spreader/sticker adjuvant, such as Audible™, can improve performance.

  • Foliar Spray using Myclotect Gallon

    Notes: Use of a spreader/sticker adjuvant, such as Audible™, can improve performance.
    Dosage: 6 oz./100 gallons water
    Timing: Begin sprays at leaf expansion when temps. are 68 degrees with continuous leaf moisture for 6+ hours.
    Re-Treatment: 7-14 days. Can be applied monthly through August.
    Myclotect Gallon
    Myclotect Gallon
    $169.00
  • Foliar Spray using Propiconazole 1.3ME T&O

    Dosage: 5-8 oz/100 gallons water
    Timing: Begin sprays at leaf expansion when temps. are 68 degrees with continuous leaf moisture for 6+ hours.
    Re-Treatment: 7-14 days
    Propiconazole 1.3ME T&O
    Propiconazole 1.3ME T&O
    $88.20
  • Foliar Spray using T-Bird 4.5L

    Dosage: 5-10 oz./100 gallons water
    Timing: Begin sprays at leaf expansion when temps. are 68 degrees with continuous leaf moisture for 6+ hours.
    Re-Treatment: 7-14 days
    T-Bird 4.5L
    T-Bird 4.5L
    $176.00

A Diagnostic Guide is designed to help you identify a pest issue and management solutions. Always refer to product label for all rates and approved uses. Some images courtesy forestryimages.org. Use of the images does not imply endorsement of treatments by forestryimages.org

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