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Assuming these oak trees were not adjacent to a newly constructed building, house, or road (within the last 2-5 years), my initial thought would be oak wilt (Ceratocystis fagacearum). Oak wilt commonly moves from diseased to healthy trees via two methods: through root grafts of adjacent oak trees and through sap-feeding beetles. If the disease is indeed oak wilt, there are several management options (1) avoid unnecessary damage to your residual oak trees, (2) removal and disposal of infected oak trees, (3) soil trenching around infected trees to prevent spread of the oak wilt fungus via root grafts, (4) systemic fungicides.
However, diagnosis without an onsite examination of your tree(s) is analogous to a medical doctor diagnosing a patient’s illness or injury over the telephone. Simply put, MOST forest/tree health questions require onsite assessment and additional analysis by a certified arborist, local University of Illinois Extension specialist, Master Gardener, or professional forester. Please call me directly (217.244.0534) for more detail and specific contact information or visit the Forest Health & Technical Assistance section of the Extension Forestry website.