Leaf Spots on Amur Maple

Leaf Spot

• Phyllosticta leaf spot (Phyllosticta minima) regularly attacks the leaves of an Amur maple tree in addition to other maples, such as the silver, red and Japanese. This fungal disease starts as circular tan spots with red or purple borders. As the growing season progresses, black, fruiting, fungal bodies begin forming inside the already-established circles. These circles eventually dry up and fall away, leaving ragged holes in the leaves.

Tar Spot

• Tar spots caused by the pathogens Rhytisma acerinum and R. punctatum appear on all species of maple, including the Amur. They produce a spotting of leaves, each of which may be as much as 2 inches in diameter. Yellow spots first form on the leaf's upper surface. As the summer progresses, a black, gooey collection of fungi resembling a drop of tar develops inside the infected yellow circle. In severe cases, the leaves fall to the ground early.

Management

• The pathogens causing both Phyllosticta leaf spot and tar spots overwinter on fallen leaves. As spring commences, fungal spores float through the air, infecting a new generation of Amur maple leaves. Raking and destroying the leaves of diseased trees in the fall is the best management technique. However, adjacent trees from nearby neighborhoods easily reinfect any tree. Fungicides are rarely necessary, as the diseases' affects are primarily aesthetic and do little actual damage to the tree itself.

Fun Fact

• Amur maple leaves are utilized as tea leaf substitutes. Different colors of dyes can are obtained from dried leaves. The foliage produces a vibrant red color in the fall, and this deciduous tree is an ideal specimen for small yards and landscapes with limited space. Creamy, white flowers appear alongside young leaves in April and May.