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What is it?

Gray mold is a common, widespread petunia plant disease caused by the family of fungi known as botrytis.

What does it look like?

A grayish or brownish area of spots may appear on the petunia flowers. Typically these are circular although they may have irregular edges. You will notice the spots multiplying, especially during wet weather conditions. The leaves and stems may also develop brown fuzzy blotches as the disease progresses. When the botrytis fungus severely overtakes a plant, the infected tissue will form a fuzzy gray or brown mold that is soft and wet to the touch.

How does it manifest?

The fungi begin by attacking petunia foliage and flowers, which are already weak or dead from another cause. The fuzzy brown and gray mold that develops contains millions of microscopic spores. Once established, the mold can invade healthy plant tissue through contacting another plant via human hands, tools or other plant to plant contact. The spores are also easily and quickly spread by wind and water. Gray mold flourishes in regions where there are cool temperatures and high humidity. Overcrowded plantings of petunias will also multiply the mold due to the quick spread of the fungus by plant to plant contact, even if only one plant is initially infected.

What can you do about it?

Apply fungicide containing chlorothalonil at the first sign of mold damage on petunia plants. At intervals of 10 to 14 days respray plants. This should be done as long as mold is visible, and combined with the careful removal of damaged sections of plants. Remove all infected flowers and foilage without touching healthy plant sections, and be sure to clean up any debris that has gathered around the base of the plants. Avoid wetting the flowers when watering plants to prevent spore spread.