Garden Detective

When it comes to trees, to spray or not to spray?

Anthracnose is a fungal disease that takes hold in tree species such as maple and sycamore in spring. It is characterized by brown or black splotches that can cause leaves to fall off in bad cases. Cool, wet spring weather exacerbates the disease.
Anthracnose is a fungal disease that takes hold in tree species such as maple and sycamore in spring. It is characterized by brown or black splotches that can cause leaves to fall off in bad cases. Cool, wet spring weather exacerbates the disease.

Experts tackle readers’ garden questions.

Q: For some years now, I have annually had three treatments applied of anthracnose spray to the two sycamore trees in the frontyard. Is that a good thing to keep doing every year or not? Several neighbors also have sycamore trees and they do not spray. The neighbors’ trees all – frankly – look about the same (if not somewhat better) in terms of leaf appearance and rate of leaf browning and drop. Also, the tree service now charges $366 for the three applications of anthracnose spray. Is that about right?

Greg Geeting, Sacramento

Sacramento County Master Gardener Linda O’Connell: Sycamore trees (Plantanus occidentalis) are large, rapid-growing trees that tolerate drought, heat, cold and smog. The California sycamore (Plantanus racemosa), which can reach 50 to 100 feet tall, is native to the California foothills and coast ranges. This species is especially susceptible to anthracnose, a group of diseases that cause dark, sunken lesions on leaves, stems, flowers and fruits. Besides infecting sycamore and other deciduous trees, anthracnose can infect evergreen trees and shrubs, as well as fruits, vegetables and turfgrass in some regions of the country.

Anthracnose results from an infection by a fungus. The genus of the fungus differs depending on the tree or plant attacked. Infections on deciduous plants are more severe in areas where prolonged spring rains have occurred after new growth appears. Because anthracnose fungi need water to disseminate and infect, the fungi do not spread in dry conditions.

Anthracnose affects developing shoots and young leaves. On sycamore trees, anthracnose lesions typically develop along major leaf veins. If the leaves are very young when infected, they can become curled and distorted, and only a portion of each leaf dies. Generally, mature leaves are resistant to infection. But when conditions are favorable, spotty lesions can occur. Heavily infected leaves fall prematurely throughout the growing season. New leaf growth usually occurs after an early drop. In California, anthracnose rarely causes permanent damage to sycamore trees.

Once symptoms develop or become severe, anthracnose cannot be effectively controlled during the current season. Because of this, some homeowners choose to spray fungicides to prevent infection. However, pesticides are not found to reliably control the disease. Complete coverage of large trees is difficult and expensive, which can make anthracnose control challenging.

Cost of a typical spray treatment will depend on the tree height and the ease at which it can be sprayed. While control might occur in some situations, anthracnose can return annually and result in a continued preventative spray program like you have been doing. The University of California Integrated Pest Management program suggests that fungicide applications for anthracnose control generally are not an option for hosts other than ash trees.

A better option is to consider environmental factors for managing anthracnose. Rake and dispose of fallen leaves and twigs during the growing season and in the fall. Prune trees during winter to increase air and light circulation in the canopy. Remove the previous season’s infected twigs and branches to eliminate locations where the fungus can survive. Redirect sprinklers so the lower canopy does not get wet.

Dry spring weather could mean that disease management is not necessary. A wet spring could result in a disease outbreak, but hopefully the preventative measures you have taken will lessen the disease’s impact.

For future reference, the Bloodgood sycamore is resistant to anthracnose. For more information on anthracnose, visit the UC IPM website at ipm.ucanr.edu.

Linda O’Connell is a UC Cooperative Extension Master Gardener with Sacramento County.

Garden questions?

Questions are answered by master gardeners at the UC Cooperative Extension services in Sacramento and Placer counties. Send questions to Garden Detective, P.O. Box 15779, Sacramento, CA 95852. Send email to h&g@sacbee.com. Please put “Garden Detective” in the subject field and include your postal address. To contact UC Extension directly, call:

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