Missourians from St. Louis to Table Rock Lake are reporting a strange condition on the leaves of oak trees. An even stranger phenomenon is occurring on the ground underneath affected trees.
The phenomena are most common between Rolla and Lake of the Ozarks. The first sign of something unusual is oak trees turning brown. Close examination shows pinhead-sized buttons on leaf bottoms. These bumps eventually turn brown and fall to the ground where they commence bouncing, as if they were alive.
In fact, something is alive in there. The balls are galls--abnormal growths sort of like tumors. They develop when tiny wasps of the Genus Cynipidae lay their eggs on tender young oak leaves. The galls provide both food and shelter for growing wasp larvae.
The bouncing is caused by vigorous movement of the larvae inside. The random motion causes the galls to settle into leaf litter and crevices where they will be protected from the rigors of winter.
People whose oaks have jumping galls are more worried about their trees than why the galls jump. Experts say the galls rarely cause significant damage to trees. They are just one of life’s irritations for healthy oak trees, sort of like fleas on a rabbit. On the other hand, oaks that have fungal infections or have suffered extensive limb loss due to ice or wind already are stressed. For these trees, the demands of replacing dead leaves can lead to long-term declines in health.
Good growing conditions and sanitation helps minimize the severity of jumping oak gall infestations. This includes watering during droughty weather and fertilizing trees in the spring. It’s also a good idea to remove fallen leaves and burn or compost them.
Although jumping oak galls are the main cause of oak trees turning brown, they are not the only cause of leaf discoloration in oak trees. Fungus infections also are causing some problems this year. This problem also seldom is fatal to oaks, and no actions are needed to help trees recover, other than those noted above.
More information about jumping oak galls is available at mdc.mo.gov/22967.