Maple Gall Mite (Vasates aceriscrummena)

Maple Leaf Gall is a red bump or tiny bubble that appears on the top of some maple tree leaves. Most commonly affected maples include the families of: Acer x freemanii, Acer saccharum, and Acer saccharinum. It can also affect other trees such as Lindens. 

A common comparison would be to consider gall like acne. Though unsightly, the good news is that gall is not detrimental to the health of your maple tree. The Ontario Ministry of Agriculture, Food, and Rural Affairs (OMAFRA) states that: “heavy infestations may completely deform leaves but seldom injure trees seriously”. Additionally, as the tree matures and establishes itself, it will outgrow this phase as the leaves become more dense and strong.

The maple is generally affected by gall in late fall. The mite hibernates in the bud of the tree during the dormant months. When the leaf opens in the spring time, the mite lays its eggs on the surface of the leaf. By the time you see the red blister, they have long gone. Therefore, treatment must be done early.

OMAFRA recommends dormant oil on the tree in the early spring, before the buds open, to kill the mite before it lays eggs. Another treatment option is to use an insecticidal soap when the leaf opens. However, many people choose to forego treatment due to the effort and cost associated with this course of action.

It is worth noting that at the end of the day this is a cosmetic issue, and as such, many chemicals that once were available for commercial sale are no longer able to be purchased in Ontario under the Cosmetic Pesticide Ban. Feel free to visit us in store for the most up-to-date information and treatment options.