What’s going on with my Oak tree?
Central Michigan oak trees are under threat from spongy moth, drought, armillaria root rot, two lined chestnut borer, and oak wilt.
Red oaks especially are being decimated by these insects and diseases. The mortality rate in some locations around Michigan are very high. If you have oak trees in your neighborhood or property that are in decline it is likely they have been impacted from one or more of these issues. It is possible that they will not recover, read on to learn more about the problems and solutions to oak decline complex.
Please read here for a more detailed, yet concise, description of the oak decline disease complex: OakHealth_InNewaygoCo.pdf
There are a few options for saving your high value oak trees. Early detection and identification is important. First knowing what is impacting your trees is vital to avoid an incorrect prescription. Most of these problems are most readily identified during the growing season.
Spongy moth will emerge in spring and summer and begin feeding on leaf parts. They can be identified by examining the caterpillars. Defoliation does not outright kill trees, but the consistent feeding pressure makes the tree more susceptible to other stressors, such as drought and Armillaria root rot. If there have been multiple years of defoliation, it may be worthwhile to inject your trees with a systemic insecticide, such as emamectin benzoate. There are foliar applications that can be sprayed but this is only practical if the tree is relatively small. Read more on spongy moth here: Dealing with Spongy Moth Around Your Home or Property - Integrated Pest Management
Armillaria root rot will present itself in a few ways, but the most positive way is with the identification of an active fruiting body (mushroom) on or near the base of the tree. The fruiting body is typically only present for a week or two, weather dependent. Crown dieback is the next most obvious indication of a fungal infection. Look here for to learn more about Armillaria: Armillaria Root Rot / Home and Landscape / UC Statewide IPM Program (UC IPM) There is little to no control for this fungal pathogen and it will continue to live on wood tissues even after the death of its host. It may spread to other weakened hosts as well. The weakening of wood strength and bendability is one important thing to be aware of when a wood decay fungus is present. Trees that are infected are much more likely to break, or fail, especially during strong weather events.
Oak wilt can be positively identified by sending plant tissue samples into a lab. However, most cases may be examined in the field and are easy to suspect before lab confirmation. Tree canopies that begin to turn brown and dieback from the top down is the most obvious identifier. Tree death can occur in as little is a few months but may take a few years. Once it begins there is not much chance of survival, species dependent. White oaks have shown more resilience to the disease and if treated with fungicides, may survive the initial attack. Red oaks tend to succumb within 1-3 years and must be preventively treated to be saved in the presence of the disease. Read more here: Oak Wilt | Symptoms, Management | The Morton Arboretum If you have or suspect the presence of oak wilt on your property, I recommend reaching out to a qualified arborist to develop a management plan. It is likely this will involve the removal of any tree that may pose a threat to valued property. Fungicide treatments, removal of infected trees, and cutting possible root grafts are three management techniques that may slow the onslaught of the disease but are not guaranteed to be effective long term.
The two lined chestnut borer is a native insect that typically attacks weakened trees. It burrows into the living tissue below the bark, disrupting the flow of nutrients and may present itself with tip dieback and large (1/4 inch) irregular holes. This pest is just another factor in the oak decline complex. It typically is not controlled with insecticide treatments since its presence typically comes on the heels of other stress factors that should be addressed first. Site management is often recommended to benefit general tree health, so that the tree can fight off this pest on its own. Reducing water-related stress is usually cited as the first method to promote tree health. Soil sampling and fertilization is the next recommended practice. After the tree’s basic needs are covered, then treatments may be recommended if the problem is not resolved.
