Sycamore Diseases & Insect Pests

Printer Friendly Version

Sycamores (Platanus species) grow on a wide range of soil types, but they prefer deep, fertile, moist, well-drained soil and full sun. Foliage diseases reduce the attractiveness and growth of trees. Repeated defoliation may put a tree under stress, which makes it more susceptible to wilts, cankers, or root diseases, as well as insects.

Anthracnose (Leaf and Twig Blight): The most important sycamore leaf disease is anthracnose caused by the fungus Gnomonia platani (Discula platani). This disease may appear as four distinct phases:

• Twig Blight: Occurs in the spring before leaf emergence, killing tips of small, 1-year-old twigs.
• Bud Blight: Occurs in April and May; the expanding buds die because of the girdling action of the canker on the branch.
• Shoot Blight: New shoots and immature leaves on infected branches suddenly die.
• Leaf Blight: The most characteristic symptom is a crinkling and browning of the leaves. Entire leaves may be killed and then fall. These symptoms are very similar to those caused by late spring frost injury.

This disease is favored by cool, wet weather (temperatures under 60 ° F during budbreak and the first few weeks of growth). A severely infected tree may be defoliated several times in a single season. Small twigs and branches may be affected, and cankers may girdle and eventually kill the branch. This will result in the production of many small shoots from the area just below the girdled portion of the branch, giving that part of the tree a bushy appearance. Spores are spread by rain and wind to healthy leaves, buds and twigs. The fungus survives the winter on fallen leaves and twigs.

Prevention and Treatment: Fallen leaves and twigs should be raked up and destroyed. Diseased branches should be pruned out and destroyed. This will limit the number of spores being produced by the fungus to start new infections. Care should be taken to sterilize pruning shears in rubbing alcohol or other disinfectant after pruning each infected branch. Adequate fertilizer and water should be applied to maintain the vigor of the tree. The cultivars ‘Bloodgood,’ ‘Columbia’ and ‘Liberty’ are moderately resistant to anthracnose. Spring applications of bordeaux mixture, copper, chlorothalonil or thiophanate-methyl fungicides may control the disease. Read and follow all directions on the label.

Powdery Mildew: The fungus Microsphaera alni is common on plants growing in shady areas. Young leaves and twigs are covered with a thin layer or irregular patches of grayish white powdery material. Infected leaves are distorted, and many may turn yellow and drop off. New growth is often stunted. In late summer, tiny black dots (spore-producing bodies) are scattered over the white patches like ground pepper.

Prevention and Treatment: Control is usually not warranted. Several fungicides may be applied, such as myclobutanil, triforine or triadimefon. Read and follow all directions on the label.

Summer Leaf Scorch: During hot weather, usually in July or August, leaves turn brown around the edges and between the veins. Sometimes the whole leaf dies. Many leaves may drop during late summer. This problem is most severe on the youngest branches. This problem may be mistaken for damage caused by anthracnose or lacebugs. However, the brown areas caused by anthracnose cross over the veins and often cover the entire leaf. Lacebugs leave brown droplets of excrement on the lower surfaces of the leaves. Physiological leaf scorch is caused by excessive evaporation of moisture from the leaves. If the roots cannot absorb and transport water fast enough to replenish this loss, the leaves turn brown and wither. The bacterial leaf scorch pathogen, Xylella fastidiosa, can also cause scorching of leaves by plugging up the water-conducting tissues.

Prevention and Treatment: To prevent scorch, deep-water trees during periods of hot weather to wet the entire root space. If practical, apply a layer of mulch over the root system. Always plant trees adapted to your climate.

Sycamore Lace Bug: Sycamore lace bug (Corythucha ciliata) gets its name from the lacy pattern seen on the adult’s wings, head, and thorax (chest region). The adult is small, ¹/8 inch in length and brown to black in color. Adults survive the winter under peeling bark of the sycamore tree. They become active in the spring at about the same time as leaves begin to develop. The adult female lays eggs on the leaf’s undersurface, attaching them with a brown sticky material. In a few days, the nymphs (immature stage) hatch. The nymphs are wingless, darker than the adults are and covered with spines. Both adults and nymphs feed on the undersides of leaves. They use their piercing/sucking mouthparts to remove sap from the leaves. Around the feeding sites, the leaf tissue turns yellow. These yellow flecks are visible from the leaf’s upper surface. Late in the summer, the lower surface of the leaf will typically be covered with dark spots of waste material and the cast off skins of immature lace bugs. Damage to trees is typically not serious, but heavy infestations can reduce growth.

Prevention and Treatment: Natural enemies of the sycamore lace bug include the following: assassin bugs, minute pirate bugs, lacewings, spiders and predaceous mites. As much as possible, these predators should be allowed to reduce lace bug populations. To control sycamore lace bugs, it is important to inspect leaves every week for signs of the insect. If the tree is small enough, spraying with a strong stream of water can control a light infestation of lace bugs. Controlling this pest on a large tree using chemicals is expensive and often not practical. The size of the tree, the need for specialized equipment and the cost may prohibit this approach. Since little serious damage results from lace bug infestation of sycamore trees, tolerating some damage is a good choice. When chemical control becomes necessary, the following insecticides are recommended for homeowner use: carbaryl (Sevin 50WP), malathion 5EC and acephate (Orthene 9.4%EC). As with all pesticides, read and follow all label directions and precautions.

NOTE: Chemical control of diseases and insects on large trees is usually not feasible since adequate coverage of the foliage with a pesticide cannot be achieved.