What's Wrong With My Hydrangea?

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. The problems are often worst in shady areas with crowded garden beds and stagnant air. People in the South have every right to panic, but instead they wisely call on me to diagnose the ailments and provide solutions. Here are five common problems with hydrangeas and how to fix them.

Ugly Ailment #1: Cercospora Leaf Spot

programs.ifas.ufl.edu/ Cercospora leaf spot. Photo: programs.ifas.ufl.edu/

We hear 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 to keep the problem from getting worse. Spray again next summer before the spots show up.

Ugly Ailment #2: Anthracnose

emAnthracnose. Photo: forums-gardenweb.com/em

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 can also be affected.

What to do: 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 Daconil or a copper-based fungicide like Bonide. Spray healthy flowers and foliage next summer before spots appear.

Ugly Ailment #3: Powdery Mildew

nickiwoo.com/ Powdery mildew. Photo: nickiwoo.com/

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: Powdery mildew won't seriously harm hydrangeas, but if you can't stand to look at it, spray the foliage according to label directions with neem oil or Natria Disease Control. Clean up fallen leaves to reduce the spread. Thin overcrowded plants to let in more light and air.

Ugly Ailment #4: Botyris Blight

This fungus likes cool, wet weather and ruins your summertime flower show, killing unopened buds and covering pretty blooms with unsightly brown blotches. You might see fuzzy gray spores growing on the flowers as well. Leaves can develop spots when infected petals drop on them.

What to do: Remove infected flowers and any debris from under the plant. Reduce overcrowding in the flower bed. Spray with a fungicide or neem oil and avoid watering late in the day.

Ugly Ailment #5: Bacterial Leaf Spot

Bacterial leaf spot first appears as water-soaked spots on the leaves, often after heavy rains and hot weather. Symptoms usually start at the bottom of the plant and spread upward. The small spots turn a dark brown or purple and become angular, sometimes expanding to grow together and create big, ugly patches. This one is most known for attacking oakleaf hydrangeas, but bacterial leaf spot can affect your smooth hydrangeas and French hydrangeas too.

What to do: Remove dead leaves from the plant and the ground. Don't wet foliage while watering. Spray with a copper-based fungicide like Bonide.