Monday, May 18, 2009

Landscape - Anthracnose of Shade Trees

The following is a good article from Rutgers on anthracnose of shade trees. This is a common disease in Delaware. Photos of sycamore anthracnose are shown in the previous post.

Anthracnose of Shade Trees

Anthracnose is a common disease of many shade tree species, particularly sycamore, ash, oak, maple, and walnut. This disease affects foliage as a scorch along leaf margins and veins, and also causes dieback and cankers to form on twigs.

Anthracnose begins its annual cycle in the spring. Small fruiting structures situated on small twigs infected the previous year produce spores. Spores are splashed and carried by wind to infect developing leaves. These diseased leaves develop lesions along veins and leaf margins, causing the tissue to appear “scorched.” In severe cases, leaves soon completely blight and fall from the tree. In some species such as sycamore, trees promptly refoliate in the drier, early summer months. These new leaves are not usually affected by the disease; anthracnose is more severe when temperatures during leaf expansion remain between 55 and 60 F, and when moisture remains on leaf surfaces for long periods of time.

In the twig blight phase of the disease, infected twigs may die back 6 to 8 inches from the tips, and larger cankers may form if infection is severe or if the tree is in poor health. Repeated tip dieback results in clusters of dead twigs called “witches’ brooms,” which are readily apparent as you look at the silhouette of the tree.

To manage anthracnose, improve plant vigor, prune cankers and dead branches, and avoid planting highly sensitive plants. Irrigate in the early morning hours and avoid over-head watering to prevent excessive moisture from remaining on foliage. Since anthracnose does not usually cause serious damage to healthy trees, application of fungicides is recommended only when it is necessary to keep trees as blemish-free as possible.

If desired, some control of this disease can be obtained with foliar applications of fungicides which include Armada, Bacillus subtilis, chlorothalonil, ConSyst, copper, (Badge, hydroxide, oxychloride, salts, sulfate), Junction, mancozeb, neem oil, phosphate (trunk injection), Quali-Pro TM/C WDG, Spectro, SysStar, thiabendazole (trunk injection), thiophanate-methyl, TwoSome (no commercial uses), trifloxystroban, or Zyban.

Information from "Foliar Diseases in the Landscape" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers Univerisity in the April 30, 2009 edition of the Plant and Pest Advisory newsletter, Landscape, Nursery, and Turf Edition from Rutgers University. Go to for the full article.

No comments: