The Q&A Archives: Black mold on apples

Question: For the last three years the apples on my Winesap trees have had a black substance on their skins. What is this and how can I control it? Pamela Freeman Hollywood, MD

Answer: It's either sooty blotch (Gloeodoes pomigena) or sooty mold fungus, says Stuart Wilson, orchard manager at Burford Brothers Nursery, growers of more than 400 varieties of apples in Monroe, Virginia. These very different problems are only cosmetic, and the apples are fine to eat, store and cook, he says. The simplest solution is to wash them after harvest with soap and water. If traces remain, peel the fruit before you eat it. Sooty mold is a fungus that lives on the honeydew excreted by aphids or scale insects when they feed on the young apple leaves and twigs. The honeydew drips onto the fruit and foliage below, turning them blackest where the honeydew is thickest. If the infestation of sucking insects is severe, the mold can cover the whole fruit, but it washes off readily. Control aphids and scale by spraying with dormant oil early in spring. Late-season aphid outbreaks are readily controlled with insecticidal soap as soon as you notice the insects. Sooty blotch is a fungus that lives on the skin of the apple, and it is a little harder to wash off. It thrives in 80 F temperatures with high humidity. You normally start seeing the irregular patches of black mold on apples in June and July, especially after rains, says Wilson. Sooty blotch often occurs with another cosmetic fungal disorder called fly speck, which causes clusters of tiny black dots on the apple skin. Winesap is especially susceptible to sooty blotch, Wilson adds. You might try growing Black Twig, a similar apple that isn't as susceptible to blotch.

« Click to go to the homepage

» Ask a question of your own

Q&A Library Searching Tips

  • When singular and plural spellings differ, as in peony and peonies, try both.
  • Search terms are not case sensitive.

Today's site banner is by cocoajuno and is called "Here's looking at you."