December’s Weed of the Month is a small tree called Amur maple (Acer ginnala). It is native to China and Japan and was introduced to North America in the 1800s as an ornamental plant. Though valued for its brilliant fall color, it has become invasive throughout the eastern and Midwestern states, including Minnesota.
Amur maple is a deciduous large shrub or small tree that grows to 20 feet. The leaves are 3-lobed with toothed margins and turn a vibrant red in the fall. It produces abundant double-winged samaras typical of maple trees. The bark is smooth and grayish brown. The plants grow in single stem or multi-stemmed clusters and is found in open woodlots, forest edges, disturbed areas, roadsides, and ornamental landscapes. Amur maple can grow in a wide range of soil types and will tolerate shade.
Amur maple spreads by seed in addition to ornamental plantings. Seed can be carried long distances by wind and water. Amur maple plants can alter habitats, invading prairies, grasslands, or open woodlands where it can add a shrub layer. Because of its prolific seed production, it can displace native shrubs, understory trees, and native herbaceous plants.
Amur maple is a Specially Regulated Noxious Weed in Minnesota and should only be planted in landscapes where the seedlings will be controlled by mowing or other means, and should be planted at least 100 yards from natural areas. Although landowners are ultimately not required to control or eradicate Amur maple on their properties, they are encouraged to manage Amur maple appropriately to prevent future spread of this species and degradation of native habitats.
Several management tactics are available for Amur maple. For all options, infestation sites will need to be monitored and treated repeatedly until the seedbanks are depleted. Stumps and sprouts that appear to have died can resprout after several years.