Maple Bladder Galls
Blister-like growths on the leaves of soft maple trees are caused by mites. These mites overwinter in the furrows of the soft maple tree’s bark. As buds flower in the spring, the mites feed on the tree’s new growth. The leaves respond to the mites’ feeding by developing the galls. The mites then live, feed, and reproduce within the maple bladder galls. At first, these growths are red and green, but they eventually turn black. Galls can cause the leaves to become deformed and to drop earlier than normal. Once formed, galls cannot be removed from the leaves. In the fall, mites move back to the bark furrows where they overwinter. Landowners are often alarmed when they notice maple bladder gall infestations, fearing that their trees will eventually die off. However, trees are very unlikely to experience any injury from these galls, and the trees’ overall health and vigor will not be affected. However, the galls can impact the aesthetic quality of the tree.
How can we mitigate this problem? No mitigation is necessary. If galls present an aesthetic issue, remove infected branches. Infected branches can then be burned or buried.
Hickory gall is also known as phomopsis gall. This is the most common gall seen throughout Wisconsin. The galls are caused by a fungus that lives on the trunk or branches of hickory trees. The fungal spores are either wind- blown or carried by squirrels and birds to nearby trees. The fungus then enters the tree through wounds and fissures in the bark. Small cankers are often lighter in color, while larger galls on the trunk are dark colored and appear to be split open. The hickory’s sap oozes from the galls as they split open. Branch wilting and branch die back may occur if the gall girdles the branch. Trunks and entire trees are usually not girdled, and tree mortality is not common.
How can we mitigate this problem? Examine hickory trees annually for galls. If found, prune branches holding the gall. Branches should then be burned or buried. Consider harvesting your hickory tree if overall health is dwindling.