What Is Maple Gall?

If you’ve noticed red bumps or tiny bubbles on the top of your maple tree leaves, you might be dealing with Maple Leaf Gall. This condition is commonly observed in maples such as Acer x freemanii, Acer saccharum, and Acer saccharinum, and it can also affect trees like Lindens.

What is Maple Leaf Gall?

Think of gall as akin to acne on the leaves of your tree. Although these galls can be unsightly, they are generally not harmful to the overall health of your maple tree. According to the Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA), while heavy infestations may cause leaves to become deformed, they rarely cause serious damage to the tree. As the tree matures, it will grow out of this phase, with new, healthier leaves replacing the affected ones.

Lifecycle of the Gall Mite

Maple Leaf Gall is typically seen in late fall. During the dormant months, the gall mite hibernates in the buds of the tree. In spring, when the buds open, the mite lays eggs on the surface of the leaves. By the time you notice the red blisters, the mites have already moved on. Therefore, effective treatment needs to be applied early in the season.

Treatment Options

OMAFRA recommends applying dormant oil to the tree in early spring, before the buds open, to kill the mites before they lay their eggs. Another option is to use insecticidal soap when the leaves have opened. However, many homeowners opt not to treat gall due to the effort and expense involved.

It's important to note that since Maple Leaf Gall is primarily a cosmetic issue, many chemicals previously used for treatment are no longer available in Ontario due to the Cosmetic Pesticide Ban. For the latest information and treatment options, feel free to visit us in-store. We can help you find the best solutions for managing Maple Leaf Gall and keeping your tree healthy.