University of Maryland Extension

Petal Blight - Ovulinia - Shrubs

  Brown diseased flowers

Small black resting structures called sclerotia will develop on the brown flower remains and will overwinter on the ground.

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This disease only affects the flower petals. The first symptoms are small water-soaked spots on the petals. These spots rapidly enlarge and cause the flower to collapse and feel slimy. This disease is most severe under warm moist conditions. Flowers blighted by other fungi such as Botrytis or those killed by frost will not feel slimy. Flowers affected by petal blight turn brown and remain attached to the plant. Small black resting structures called sclerotia will develop on the brown flower remains and will overwinter on the ground. Sclerotia can survive as long as two years in the soil and will start the infection cycle in the spring.

water soaked spots on azalea flower petals
Water soaked spots on petals.

azalea flowers collapse and turn brown
Flowers collapse and turn brown.

Control
The use of a systemic fungicide such as triadimefon (Bayleton, Strike) when the flower buds first show color will give adequate control for about four weeks. Other fungicides such as chlorothalonil (Daconil 2787) and Mancozeb (Dithane F-45) will give protection for 7 to 14 days depending on weather conditions. Fungicide sprays are not effective on buds not showing color or flowers that are already open. It is a good practice to spot spray only the plants with flower buds showing the first bit of color, as opposed to spraying an entire planting of azaleas. This reduces unnecessary pesticide use.

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