A Good Year for Oak Galls

A Good Year for Oak Galls

“What are those small, white balls in my lawn?” and “There are white, fuzzy things all over my plants…are they harmful?”  These are the questions that are coming into the garden center right now. Those small balls, the size of a pea or slightly larger, are wooly oak galls. They are made by a tiny wasp, Callirhytis lanata, who lays eggs in the leaf tissue early in the season. The galls form over the summer and fall to the ground in October, and the wasp emerges again in springs to come, often two or three years later.

Let’s cut right to what you want to know: are they harmful? Short answer: No.

Are they interesting? Yes! These wooly galls are just one of the many types of oak gall that are caused by gall wasps or gall flies. They come in a variety of sizes, shapes and color, and they seldom harm a healthy tree. You might find round, papery, brown balls a bit smaller than a golf ball attached to fallen leaves or rolling loose on the ground in the fall. On the Cape and Islands we also find galls that look like tiny peaches or small BBs. Some of them are beautiful, others weird or just plain interesting. But none of the galls we find in this area hurt the plants.

Like other insects, populations rise and fall, and this year (2018) seems to be a great year for wooly oak galls. Read more about oak galls in an article written by Debbie Lester, a horticulture educator for Cornell Cooperative Extension Orange County. Oaks aren’t the only plants that can have galls form on the leaves. Read about other types of galls on this Missouri Botanical Garden site.

Small, fuzzy balls can be found on Cape Cod lawns and gardens right now.

And while we’re talking about things falling from the trees, I’ll remind you that a large crop of acorns in no way predicts a hard winter. (Come into the store an pick up a copy of Coffee for Roses, the book that addresses this and 70 other common garden myths.)

The width of the stripes on the wooly bear caterpillar (Pyrrharctia isabella, the isabella tiger moth) and the number of acorns in no way predict future weather and the winter conditions we’ll be dealing with. 

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