Leaf Diseases of Red Japanese Maple Trees

Red Japanese maple trees (Acer Palmatum), deciduous members of the Aceraceae plant family, naturally occur in Japan and typically perform well in United States Department of Agriculture (USDA) Zones 5 to 8. The Missouri Botanical Garden reports that mature red Japanese maples typically range from 8 to 20 feet in height with similar spreads. These hardy trees are somewhat susceptible to several common leaf diseases.

Anthracnose

Red Japanese maple trees often suffer from anthracnose, a leaf blight disease prevalent in warm, humid climates. Initial signs generally include small, red to purple spots forming on the leaves. These lesions frequently enlarge and merge to cover the entire leaf. The fungal pathogens (Kabatiella apocrypta) sometimes form spore masses on the undersides of affected leaves. Severely infected trees often suffer from premature leaf drop. This leaf disease causes no permanent damage. Control includes spraying with fungicides and improving air circulation.

Botrytis Blight

Botrytis blight, also called gray mold, sometimes affects red Japanese maple leaves. The fungal pathogens (Botrytis) thrive during wet weather conditions in spring and summer. Signs include brown spots appearing on the maple leaves. Some infected leaves develop silvery spore masses on dead tissue. Botrytis blight disease spreads by splashing water and wind gusts. Control includes pruning out and discarding affected leaves, improving air ventilation and applying fungicides.

Verticillium Wilt

Veticillium wilt disease often devastates red Japanese maple trees. Symptoms typically appear in July and August following stretches of cooler weather. Signs include yellowing, scorching or wilting leaves. All of the leaves on an infected branch tend to wilt very suddenly. Sings of an acute infection includes curling or drying leaves. Caused by soil-borne fungal pathogens (Verticillium dahliae), verticillium wilt spreads primarily by infected gardening tools. Treatment includes pruning out and discarding infected leaves.

Phyllosticta Leaf Spot

Red Japanese maple trees often suffer from Phyllosticta leaf spot of maple. This fungal disease (Phyllosticta minima) causes the formation of tan lesions with red or purple borders. Black fruiting spores appear inside of the lesions as the disease matures. While this maple disease causes unsightly leaves, it rarely causes severe damage. Phyllosticta leaf spot pathogens thrive in humid climates and overwinter in fallen maple leaves. Control includes raking up and destroying fallen debris and pruning out dense growth to improve air circulation.

Pseudomonas Tip Blight

Pseudomonas tip blight, a bacterial disease (Pseudomonas syringae), thrives in cool, wet climates and spreads by insects, rain and wind. This disease causes infected red Japanese maple trees to form necrotic leaf spots and discolored leaf veins. Affected branches usually suffer from tip dieback when the disease matures. Pseudomonas tip blight typically affects maple trees already weakened by other conditions, particularly frost injuries. Control includes pruning out and discarding infected leaves and branches.

Tar Spots

Maple tar spot disease, caused by fungal pathogens (Rhytisma acerinum), commonly affects red Japanese maple trees growing in moist environments. Initial signs include yellow or light green spots appearing on the upper surfaces of leaves. Black, sticky fungal spores form inside of the lesions. The plant tissue around the sores turns brown. Some infected maple trees also suffer from premature leaf drop. Control includes raking up and destroying fallen leaves every autumn.