Gardening: Pruning Trees Now Can Help Prevent Oak Wilt

January isn't usually the time of year to think about gardening, unless you're thinking about taking outdoor Christmas decorations out of the garden. However, due to a deadly disease spreading to our best tree, the venerable oak, we should only consider pruning oak trees in mid-winter to reduce the risk of infection. . the causative agent of oak wilt. Cut wounds during the growing season attract insects that spread the disease, and we can prevent the potential spread of this disease to the ground by pruning during the winter months.

What is oak wilt?

Oak spot is a very serious and often fatal disease of oak trees, especially oaks in the red or black oak groups. The fungal pathogen ( Bretziella fagacearum ) that causes the disease has been known in Ohio for decades. Some years seem worse than others. Oak inlay spreads rapidly, almost like a tidal wave moving in one direction, not unlike the damage done to ash trees by Ash Emerald. Oak blight spreads to other oak trees but is slower growing, but even then it can kill trees within a season and often within weeks. If left unchecked, it can spread further or move into an oak-dominated landscape, park or forest.

Fungi attack the water-permeable tissues of the tree. While the fungus is on the wood, it also causes a protective response from the wood to prevent the fungus from spreading. This tree reaction disrupts the absorption of water from the tree roots to the branches and leaves of the tree canopy. The result is wilting, browning from the tips of the leaves inward to where they attach to the branch.

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How does the oak tree propagate?

The fungal pathogen that causes oak wilt can be spread in two ways. The fungus is spread by sap-sucking beetles (Coleoptera: Nitidulidae) attracted to the scent of the seeds when oak trees are pruned or otherwise damaged. These insects are active during the growing season, especially in the spring, when many homeowners take advantage of the warm weather to trim shade trees and other shrubs.

The fungus can also spread from an infected tree to other nearby oak trees with roots planted underground. This usually occurs when several mature oak trees grow close together in a wooded setting, such as a park or other wooded area. Individual oak trees in the native landscape are not subject to this underground transmission pathway.

Red oak is more sensitive

Although all oak trees are susceptible to oak wilt fungi, those in the red or black group; Black, hemlock, northern and southern red, red, oak, and oak are extremely susceptible and may die within weeks of infection. Oaks in the white group, including scrub, chinquapin, post, swamp white, and white oak, are more disease tolerant and may even survive an infection for a year or more with reduced symptoms.

During the initial infection, the leaves of large branches or twigs wilt. This is called tagging. The leaves on these branches fall prematurely, and by mid-spring the tree looks more autumnal. After that, the mushrooms will continue to migrate through the trees.

Oaks growing near other oaks are more prone to oak wilt.

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Diagnosis of oak wilt

Not all symptoms of oak wilt can be attributed to oak wilt fungi. Drought, insect damage, soil compaction, and other abiotic factors can cause symptoms similar to oak wilt. The only way to determine if a tree is infected with the oak wilt pathogen is to test the branch for the pathogen in the laboratory. ODU's Plant and Pest Diagnostic Clinic performs these types of tests; For more information on submitting a test pattern, visit https://ppdc.osu.edu/.

More information on oak wilt can be found here: https://ohioline.osu.edu/factsheet/plpath-tree-02.

Mike Hogan is a teacher and associate professor of extension, agriculture and natural resources at The Ohio State University.

hogan.1@osu.edu

This article was originally published in The Columbus Dispatch. Gardening. Pruning the tree now can help prevent oak wilt