SHADE TREE ANTHRACNOSE

    What is that?

    • Anthracnose is a leaf disease caused by fungi that are active in the early spring.
    • It can highly disfigure leaves on susceptible trees, and this very noticeable damage often concerns homeowners greatly, especially in the spring.
    • Shade tree anthracnose is separate from dogwood anthracnose, which is a different disease caused by a much more virulent fungus that requires early and aggressive management.

     

    What causes shade tree anthracnose?

    • Fungi of the genus Discula (and related forms) are responsible for this disease.
    • The fungi pass the winter on dead leaves on the ground, or occasionally in cankers on affected twigs in the trees. In the early spring, their spores are dispersed for reinfection.
    • Anthracnose fungi can only affect leaves under cool and moist conditions typical of early spring. When the weather warms up and dries out, infection can not occur.

     

    What does it look like?

    • The symptoms include irregular, brown-black blotches, sometimes paralleling the leaf veins.
    • When the weather is particularly favorable (lengthy cool and moist period), entire leaves can become blighted and significant tree defoliation can occur.
    • Some important landscape and street trees are particularly susceptible. They include maples, ashes, sycamores, beech, birch, elm, walnut, and horsechestnut.

     

    What should be done about this disease?

    Ø Take a healthy dose of tolerance. Since this disease will stop as the weather becomes warmer and drier, there is no need for control measures in most cases.
    • Even if defoliation occurs, the tree will put out its second flush of growth under warmer and drier conditions that prevent infection by the fungus.
    • To help reduce the infection level the following spring, remove and discard the leaves from a diseased tree in the fall-- or compost them properly.
    • If anthracnose is serious near a new planting site, select trees that are resistant to it.
    • Fungicides are rarely recommended because this disease usually does not affect the overall health of the tree.

    -- If anthracnose is a recurring problem and/or the tree is on a prominent site, where the damage is esthetically unacceptable, a fungicide program may be warranted.

    -- Initiate any fungicide treatment before budbreak; by the time symptoms can be seen, it is too late. Check Cornell Recommends for products, dosage, and timing.

     

    Where can I get more information?

    G. W. Hudler, W. A. Sinclair, and W. T. Johnson, 1985. "Anthracnose Diseases of Trees and Shrubs." Cornell Tree Pest Leaflet A-2. If you want this publication or other information on this topic, call your regional DEC or Cooperative Extension, contact the Distribution Center at Cornell, or call us at the Community Forestry Education Project, 716-461-1000.

    BORERS

     

    What are they?
    • The word "borers" applies to all wood-boring insects, including moths, beetles, sawflies, horntails and flies. Most of the damage is done when they are in the larval stage.
    • Borers attack urban and rural forest trees, causing wood defects and weakening the tree.

     

    What are the exterior signs of the presence of borers?
    • Dead tree, dead top of tree, dead limbs or branches, or branches that lack vigor.
    • Exit holes, where the insect has left the tree, that range in size from a pinhead to 3/4".
    • Sawdust at the entrance of exit holes, or on the ground beneath.

     

    What kind of interior damage do they cause?
    • Adult boring insects deposit their eggs beneath the bark by piercing or chewing through it.
    • Once hatched, the larvae feed by tunneling through young shoots, branches, trunks, or roots.

     

    Why are borers a serious threat?
    • They kill trees, both old trees and young trees.
    • Loss of terminals, branches and trunks weakens and deforms the entire tree.
    • In municipal settings, trees with borers become hazardous when their wood is weakened.

     

    What trees are susceptible?
    • Trees suffering from environmental stress such as prolonged drought or site that is not suited to the species.
    • Storm-damaged trees: their weak condition and open wounds are inviting to insect borers.
    • Transplanted trees, especially when not watered the first year or two.
    • Young nursery plantings growing near infested areas.
    • Common examples include white birch, European mountain ash, crabapple, and black locust.

     

    How should this problem be handled?

     

    • Plant the right tree in the right location in the first place.
    • Minimize environmental stress, especially on young trees (e.g., with summer watering).
    • Get a positive identification. There are many different species of insect borers, and each one has a different life cycle, therefore requiring different timing on treatments.
    • Remove dead or damaged wood, and be sure pruning cuts are made properly.
    • For details on treatments, consult a current Cornell Recommends: Trees & Shrubs.

     

    Where can I get more information?

    Warren T. Johnson and Howard H. Lyon, 1991. Insects that Feed on Trees and Shrubs. 2nd edition, revised. Ithaca: Cornell University Press. If you want to consult this reference book for a discussion of a particular species, or to get other information on this and related insect topics, call your regional DEC or Cooperative Extension, or us directly at the Community Forestry Education Project, 716-461-1000.