According to the USDA Forest Service, management solutions are urgently needed to cope with the large number of oak trees that are declining in our northern forests. Trees affected by root diseases like Phytophthora and Armillaria can lose capacity to absorb water and nutrients. This further weakens the trees and favors secondary issues such as infestation by two-lined chestnut borer. This spring, District staff observed secondary infections of Hypoxylon cankers in red oaks.
The Park District has been working to address oak decline since 2019 when it began a series of annual preventative treatments in our trees at Sunset Woods Park. Recently, the District reached out to The Morton Arboretum for assistance in the effort.
Starting this August, the District is participating in a Morton Arboretum study to treat and track the health of declining oaks. Arboretum staff visited Sunset Woods and Heller Nature Center to test for Phytophthora, a soil-borne root rot disease. Species of Phytophthora produce spores that can survive for years in moist soil and can travel through water to infect a living host.
Selected trees were treated for Phytophthora using a phosphonate fertilizer that has fungicidal properties. For some trees, treatment also included an application of a growth regulator to allow the trees to direct energy away from their canopy and into their roots. This approach will also be used by the District at Sunset Woods in areas where soil has been compacted due to heavy use. A total of eight trees (four white oaks at Sunset Woods and four red oaks at Heller Nature Center) are part of the ongoing study.
Separately, the District has tagged trees in Sunset Woods Park for treatment for root disease. In the next few weeks, the District will treat those trees using a hand-held spray to apply phosphonate fertilizer around the bark and root crown (where tree meets soil). Also, 60 of the trees will be treated for two-lined chestnut borer.
Fortunately, many of the trees in Sunset Woods are Swamp White Oaks that are tolerant of wet conditions. Also, the District has been proactive about planting new trees. For example, since 2015, Arbor Day volunteers have been planting 20 trees a year in the park. No mow areas around the park also help protect vulnerable trees from damage. For more information, contact Rebecca Grill, Natural Areas Manager, email@example.com.