French hydrangeas may be water hogs, but extended periods of wet weather can cause them big problems. Suddenly, their pristine leaves become spotted, scorched, and dusted with powder. People in the South have every right to panic, but instead they wisely call on me to diagnose the ailments and provide solutions. Once again, Grumpy delivers.
Ugly Ailment #1 -- Cercospora Leaf Spot
Grumpy gets more panicked emails about this fungal problem than any other. Small brown or purple spots appear on the leaves. As they grow in size, they develop tan or silver centers with purplish borders. Lower leaves are affected first. Then the disease moves up the plant as splashing water from rain or sprinklers spreads the spores. Seriously infected leaves drop.
What to do: First, pick up, bag, and throw away any fallen leaves to reduce the number of fungal spores. Second, don't wet the foliage when you water. Third, spray the foliage according to label directions with Immunox, Daconil, or Natria Disease Control. Spray again next summer before the spots show up.
Ugly Ailment #2 -- Anthracnose
Like leaf spot, this malady likes warm, wet weather and spreads by splashing water. Brown spots appear on the leaves and grow rapidly in size. Light-brown centers surrounded by dark-brown rings create a bull's-eye effect. When a spot encounters a leaf vein, it spreads along it, forming an angular brown or black patch. Leaves turn dark brown or black and drop. Flowers may also be affected.
What to do: Write Grumpy a $50 check for being such a font of wisdom. Pick up, bag, and throw away any fallen leaves. Don't wet leaves and flowers when watering. Spray foliage and flowers according to label directions with Natria Disease Control or a copper-based fungicide. Spray healthy flowers and foliage next summer before spots appear.
Ugly Ailment #3 -- Powdery Mildew
Small, gray to white patches appear on the leaves. They eventually coalesce, covering the leaves with a powdery white film. Unlike the previous two diseases, powdery mildew likes both cool and warm, humid weather. But the leaves must be dry for the spores to germinate on them.
What to do: Write Grumpy a second check for $25 so he can leave work early and buy a nice bottle of red wine for tonight's dinner. Spray the foliage according to label directions with neem oil or Natria Disease Control.
Related stories you will learn from and enjoy: "Why Your French Hydrangea Never Blooms"