It’s Plum Season! But Beware, This is Not a Plum

Inquiring Marylanders want to know: Are these fruits that fell from an oak tree?

We received a couple questions this season from curious residents of Montgomery County who found “fruits” that look like small plums. These objects had dropped from oak trees.

While these fruit-like items do look similar to plums, they are not edible at all! These are acorn plum galls, which are caused by a type of wasp in the family Cynipidae.

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Why are Oaks Declining? Dr. Dave Describes 3 Oak Diseases

oak wilt symptoms
Leaves showing oak wilt symptoms, Pittsburgh, PA (Photo: Dave Clement)

We’ve recently received inquiries about oak trees declining and dying. People usually want to know if this is caused by oak wilt. Importantly, oak wilt is not known to occur widely in Maryland. Two common leaf diseases of oaks in Maryland are oak anthracnose and bacterial leaf scorch of oak.

oak anthracnose
Oak anthracnose

Oak anthracnose is caused by a fungal pathogen, Apiognomonia quercina, and it typically is a cool, wet weather, springtime disease. In wet cool summers like the one we’re experiencing this year however, the symptoms can continue through the season. Most oak species will show a range of symptoms scattered through the leaf canopy. Symptoms range from small brown spots and irregular dead areas on distorted leaves to severe blight that kills twigs and causes leaf shriveling. This disease in oaks typically doesn’t cause much leaf drop.
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