Quick Facts...
- The most serious disease of sycamore trees is anthracnose.
- Anthracnose often is confused with frost damage.
- The first symptoms appear on young leaves as they unfold.
- Older leaves turn brown, and dead areas occur along the leaf veins. Brown areas eventually enlarge to include the whole leaf.
- The ends of twigs may be killed back 8 to 10 inches.
- Cankers may develop on the tree trunk and main branches.
Anthracnose is the common name given to a group of fungal pathogens which
cause dark, unually sunken lesions. The term anthracnose is from the Greek
word for coal or charcoal. These are typically diseases of leaves, stems
or fruits. The sycamore anthracnose fungi attack sycamore trees early
in the spring, causing a rapid wilt of newly emerging leaves. This rapid
wilting is frequently misidentified as frost damage. Larger, more mature
leaves develop a brown growth along the main veins. Infected leaves often
curl and eventually fall, littering the ground. The fungus involved is
Apiognomonia errabunda & veneta (synonyms = Gnomonia errabunda &
veneta); anamorphs = Discula umbrinella & platani.
The sycamore leaf is naturally fuzzy. Do not confuse this natural fuzziness
with infection by anthracnose fungus.
Cankers
Cankers often form on the twigs and branches at the base of blighted leaf clusters. These cankers become active the following spring and produce spores. These spores reinfect the tree and spread the disease to other sycamore trees in the area.
Cankers also develop in larger branches, girdling and eventually killing them. Small, black fruiting bodies of the causal fungus appear in the discolored bark of dead twigs and branches.
Repeated annual killing of twigs results in clusters of old dead twigs and live branches ("witches' brooms").
Weather Influences
Weather determines the severity of anthracnose. Frequent rains and cool temperatures promote the disease. If the average temperature during the two-week period following emergence of the first leaves is below 55 degrees F, the shoot-blight phase of the disease will be serious.
Disease intensity decreases as the average temperature increases from 55 to 60 degrees. Little or no anthracnose will occur if average temperatures during this susceptible stage are above 60 degrees.
Treatment
Apply sprays as buds begin to swell. During rainy springs, additional
applications are needed at 7 to 14 day intervals until conditions for
this disease are no long favorable (see Weather Influences section
above).
A second crop of leaves may be produced from mid-June into July after loss of the first set. Protect this second set of leaves with fungicide sprays if cool, moist conditions exist.
Fungicides registered for the control of sycamore anthracnose include
chlorothalonil (Daconil Zn, Daconil Ultrex and Daconil Weather Stik. REI
= 12 hours), thiophante-methyl (3336TM F and 3336TM WP. REI = 12 hours)
and copper fungicides. REI = restricted-entry interval. Do not enter or
allow workers entry into treated areas during this period following fungicide
application. The REI varies with the copper product. Refer to labels for
specific information.
The recommended fungicides usually are readily available to homeowners
at local nurseries and Garden centers. Always read label directions. Labels
may be updated yearly or more often. If the product label does not include
anthracnose or ornamentals (shade trees), use an alternative product.
Cultural Practices
Gather and destroy all fallen leaves and twigs. They will produce fungus spores the following spring if not destroyed.
Prune out all infected twigs and branches and destroy them. Cut out cankers in large limbs to reduce reinfection. Remove the dead, cankered tissue down to healthy wood.
Dry winters weaken trees, increasing the effects of diseases. To reduce this
problem, water trees once a month during snowless winters. Water when
air temperatures are above freezing and early enough during the day to
allow water to soak in before nightfall. For more information on winter
watering, see fact sheet 7.211, Fall and Winter Watering.
In the spring after leaf emergence, fertilize trees suffering from repeated attacks of anthracnose, as evidenced by twig dieback and lack of vigor.
Resistance
The American sycamore is much more susceptible to anthracnose than the
London and Oriental plane. Due to this high susceptibiligy, planting of
the American sycamore should be avoided. The Oriental plane, a shorther,
less graceful tree, is highly resistant to anthracnose but rarely grown
in the United States. The London plane tree (P. x acerifolia, synonyms
P. x orientalis x P. occidentalis or P. hybrida) is a cross between the
Oriental plane (P. orientalis) and the highly susceptible American sycamore
(P. occidentalis). The London plane cultivars, Bloodgood, Columbia and
Liberty are resistant to anthracnose and are good choices for planting
in Colorado.
References
Dickman, M.B. 2001. Anthracnose. Page 43, in: Maloy, O.C., and Murray,
T.D. eds. Encyclopedia of Plant Pathology, John Wiley & Sons, Inc.,
New York, NY.
Hartman, J. 2001. Sycamore and planetree diseases. Pages 355-359, in:
Jones, R.K. and Benson D.M. eds. Diseases of Woody Ornamental and Trees
in Nurseries. APS Press, St. Paul, MN.
Sinclair, W.A., Lyon, H.H., and Johnson, W.T. 1987. Diseases of Trees
and Shrubs. Cornell University Press, Ithaca, NY. 574 pages.
Influence of Environment and Inoculum Density on Penetration and Colonization
of Sycamore Leaves by Apiognomonia veneta. Ammon, V., Graves, B. and Griffin,
D. Plan Dis. 74:989-991.
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