Oak trees in the Kansas City area have been declining. While the decline has been mostly due to site factors and environmental extremes, Kansas State University’s Turfgrass and Landscape Research and Extension Department says the rise of oak wilt and biscogniauxia (hypoxylon) canker in 2019 has contributed to the issue.
Oak wilt has been confirmed in red oaks in the Kansas City area, including Johnson County, while biscogniauxia canker has become common throughout Kansas and Missouri, frequently affecting oaks stressed by drought. Both diseases can kill trees, but one moves fast and spreads while the other requires stress to become active.
Understanding Oak Wilt
Oak wilt (Bretziella fagacearum) is a vascular disease that disrupts a tree’s water movement. It spreads through root grafts between nearby oaks and Nitidulidae beetles or other sap-feeding insects that transport fungal spores from infected to healthy trees. Spread most often happens during the April – June window when oaks are typically pruned. Red oaks are especially susceptible to oak wilt and can die within a single season.
Symptoms of Oak Wilt
Oak wilt appears on trees with these symptoms: partial leaf discoloration where leaves appear tan or brown at the tip and green at the base, leaves of all colors falling from a tree, and sometimes dark brown streaks in the sapwood appearing beneath the bark. Laboratory testing is still required for a definitive diagnosis.
“Red oaks often die within weeks to months of first symptoms. Regular inspections and quick action to contact your local arborist are necessary to stop the spread,” says Dr. AD Ali of the Davey Institute.
How Oak Wilt Spreads in Kansas City
There are two typical pathways where oak wilt spreads. One is through insects that appear during active oak bleeding. The other is through overland root grafts between oak trees.
Insects like nitidulid beetles feed on the sap of oak trees. On infected red oaks, spore mats form and the beetles pick up spores while feeding on the sap. When these beetles then go to feed on the sap of healthy trees, the disease spreads from the movement of spores. The best way to stop this spread is to avoid pruning between March 1 and November 15, when the beetles are most active, and to immediately seal fresh oak wounds as they are made.
Root graft transmission occurs when roots from nearby oaks grow into each other and fuse, forming a living connection that is shared between trees. When one tree is infected, the oak wilt can travel through the sap directly into neighboring healthy trees.
Understanding Biscogniauxia Canker
The biscogniauxia fungus (Biscogniauxia atropunctata) causes cankers when trees are weakened by stress from drought, construction damage, compaction, and other stressors. In healthy trees, the fungus is present without causing harm. Unlike oak wilt, biscogniauxia canker doesn’t become active unless a tree is stressed. According to the Missouri Department of Conservation, outbreaks of biscogniauxia canker typically follow severe drought events, with trees showing symptoms triggered by dry conditions 1 to 2 years prior.
Symptoms & Signs of Biscogniauxia Canker
The most distinctive sign of biscogniauxia canker is bark shedding in large patches, revealing fungal mats that appear tan, silver, or gray in their early stages and asphalt-black when mature. The fungal mat is highly visible and sometimes described as looking like thick paint on the side of the tree.
Canopy thinning, dieback starting at the top of the tree, epicormic sprouts on the trunk, and unusually small leaves are also symptoms of biscogniauxia canker.
Oak Wilt vs. Biscogniauxia Canker: Side-by-Side Comparison
While both oak wilt and biscogniauxia canker are fatal, knowing the difference between the two is necessary to properly treat your tree. Read the table below comparing the two diseases.
Feature | Oak Wilt | Biscogniauxia Canker |
Cause | Fungus (Bretziella fagacearum) – vascular disease | Fungus (Biscogniauxia atropunctata) – stress disease |
Primarily Affects | Red oaks, pin oaks; also white oaks (more slowly) | Oaks (primarily red oaks), maples, hickories, and other hardwoods |
Spread | Spreads tree-to-tree via roots or insects | Already present in many trees |
Distinctive Visual Sign | Partial leaf browning (tan or brown tip, green base); leaves of all colors dropping | Large patches of peeling bark; silver/gray or black fungal mat |
Tree Survival | Red oaks: usually fatal within one season White oaks: Die over years if not treated | Always fatal once symptoms appear in main stem; trees may linger 1–2 years |
Treatment? | Can be prevented with propiconazole injection performed by a professional if caught early; root graft disruption | Can be pruned out if first appears on branches, no effective treatment once main stem is infected; focus on prevention by reducing tree stress |
Pruning Timing | Dormant pruning in December through February in the KC area | Dormant pruning is safest for all oaks because of threat from oak wilt |
Why Accurate Diagnosis Matters
Misdiagnosis can be risky. It can lead to incorrect treatment and waste money. Fungicide injections won’t protect oaks from biscogniauxia canker, but can prevent oak wilt. Failing to act on oak wilt can mean losing additional trees oaks on your property.
“A certified arborist with lab-backed diagnostics is the only reliable way to confirm oak wilt,”
Prevention: Keeping Kansas City Oaks Healthy
Prevention is key to keeping your oak trees healthy. For oak wilt, avoid pruning oaks from March 1 – November 15, and always seal wounds immediately to prevent spread via sap-feeding insects. Biscogniauxia canker prevention starts years before symptoms appear with good tree care during droughts. Keep trees stress-free with adequate watering and mulch and avoid construction damage to prevent biscogniauxia canker.
Protect Your Kansas City Oaks With Davey
Davey’s arborists, backed by research from the Davey Institute, diagnose and treat diseases such as biscogniauxia canker and oak wilt. Contact Davey’s local office in the Kansas City area to learn more.
