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Sunset Woods Tree Care Update

9/16/20 – Last summer, approximately 40 trees in Sunset Woods Park were treated with an application of phosphonates (in a salt formulation brand name Reliant) as a preventative treatment for a soil-borne fungus called Armillaria. We are glad to report that only five were found in poor condition this spring among the treated trees. Further study showed that those trees were damaged by the presence of another tree pest, the two-lined chestnut borer.

 Following positive results from the initial treatment, but the continued presence of Armillaria in the park, the District now plans to retreat about 20 trees and treat additional trees to ensure continued health. Contractors for the District will be using handheld sprayers to apply Reliant mixed with water to the bark and root crown (where the tree meets soil) of approximately 65 trees in Sunset Woods Park identified as susceptible to, or recovering from, Armillaria fungal disease.

Approximately 20 trees will also be treated with an insecticide trade-named Dinotefuran to control the two-lined chestnut borer. Precautions will be taken to minimize impacts on beneficial insects. 

This work is scheduled to take one to two days, beginning after September 21, 2020. Signage will be posted, and Park District staff will be on hand to answer questions. As a precaution, two playgrounds in the park will be closed during the work, and treated trees will be fenced off for 12 hours following treatment. Signs will be posted.


Questions? Please contact Rebecca Grill, Natural Areas Manager, at

For more information about Armillaria, click here.