If you have pink or blue Hydrangeas, there’s a good chance that you have seen spots and blotches on the leaves. These spots are likely caused by one of two types of fungus that affect big leaf hydrangea. Here’s how to identify each type, and what to do about it.
Antracnose starts in the summer during hot and humid weather. It’s characterized by brown spots and irregular blotches, often running along the veins of the leaf.
Another variety is Cercospora. Cercospora leaf spot is a fungus marked by tan spots with purple rings around the center. This fungus is at its worst from mid to late summer.
Both of these diseases are spread easily when the leaves of the hydrangea are allowed to stay wet with water droplets. The good news is that although the leaves might look terrible, these diseases rarely kill the plant.
To prevent this from happening next year, first collect and dispose of all the leaves this fall and winter. Next spring, try to avoid excessive sprinkling of the leaves when watering. If you have to wet the leaves, do so in the morning so the leaves can dry by nighttime.
Lastly, consider spraying with a copper-based fungicide. After the leaves are formed, you’ll need to repeat the fungicide application to stay ahead of the disease. There’s nothing wrong with spraying the leaves after they’re spotted with the fungus, but it’s not likely that those spots will go away.
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