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Smart Gardening to prevent oak wilt

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Oak leaves showing oak wilt symptoms. Photo by Monique Sakalidis, MSU.

Prevent oak wilt!

By Monique Sakalidis, MSU Department of Forestry, and Ruth Dorando Marcy, MSU Extension

  • When possible, prune oaks in winter. Especially avoid pruning mid-April to mid-July.
  • Immediately seal wounds on oaks damaged during the growing season.
  • Don’t move firewood.

History and range of oak wilt

Oak wilt, caused by the fungal pathogen Bretziella fagacearum, was first reported in Michigan in the 1970s. It is now found in 56 counties with potential to impact at least 149 million red oak trees across over 20 million acres of Michigan land.

Trees at risk

Red oaks, those with bristle-tipped lobes, die rapidly from oak wilt within four to six weeks. Red oaks in Michigan include northern red oak, black oak, northern pin oak, pin oak, scarlet oak and shingle oak.


White oaks, those with rounded lobes and no bristles, or with large regular teeth, will slowly decline and likely die. White oaks in Michigan include white oak, swamp white oak, bur oak, chinquapin oak, chestnut oak and dwarf chestnut oak.

Symptoms and signs

Note the pointy, bristle-tipped lobes on this northern red oak. Bristles indicate the species is a red oak. Photo by Paul Wray, Iowa State University, Bugwood.org.

When an oak tree is infected, the fungus grows throughout the water-conducting xylem vessels and the tree responds by producing structures called tyloses to attempt to wall in the fungus. This blocks water flow through the tree, causing the wilt symptoms seen with this disease.


An infected tree is often first noticed when leaves suddenly drop or turn brown in the summer months. Leaves may be brown, somewhat bronzed or partially green. Red oak trees may be dead and defoliated within four weeks of infection.

This white oak can be identified by its rounded lobe leaves. Photo by Chris Evans, University of Illinois, Bugwood.org.

Since there are other pest, pathogen and environmental problems that may cause symptoms similar to oak wilt, a branch sample must be sent to a diagnostics laboratory for an accurate diagnosis. On trees that have been dead for six to 12 months, a mycelial mat may be visible underneath a bark crack. Presence of a mycelial mat or laboratory verification from a living tree that is showing symptoms are the only ways oak wilt can be confirmed.

How oak wilt is spread

Oak wilt spreads rapidly in multiple ways.

An oak with symptoms of oak wilt. Photo by Monique Sakalidis, MSU.
  • Overland transmission occurs when Nitidulid beetles (commonly called sap beetles) pick up spores while feeding on mycelial mats on infected trees then transfer them to fresh wounds on healthy trees. This creates new sites of infection (infection centers).
  • Underground transmission occurs when fungal spores move between connected roots (root grafts) of infected and healthy oaks. This type of spread outwardly expands pockets of dead trees (infection epicenters).
  • Moving wood from infected oaks can start infection sites because mycelial mats can form on wood cut from infected oaks, providing a source of infection.

Prevention

Prevent overland transmission of oak wilt by strictly following guidelines for safest pruning times and care of trees damaged during spring and summer. The safest time to prune is in the winter months when sap beetles are not active. The worst time is mid-April to mid-July when beetles are most likely present. Some beetles will be active throughout the summer and early fall. If a tree is damaged and pruning is required during the warm growing season, seal all wounds immediately—sap beetles can arrive within five minutes!

A sap beetle feeds on a mycelial mat. Photo by Wisconsin DNR.

Avoid underground transmission of oak wilt by severing root connections between infected and healthy oaks. Trenching equipment is used to cut a 5-foot deep line into the earth separating roots of dead and infected oaks from the unaffected oaks in the area. Trench lines are plotted using a formula that takes many factors into account and are best determined by a certified arborist or forester trained in oak wilt management. Injections of a fungicide with propiconazole as the active ingredient may offer protection of nearby valuable, healthy oak trees. This fungicide treatment will not protect against overland spread of oak wilt.

Root grafts are connected roots between trees where fungal spores can move from infected to healthy oaks. Photo by Ronald F. Billings, Texas A&M Forest Service, Bugwood.org.

To prevent the spread of oak wilt via firewood, dispose of wood from trees killed by oak wilt by burning it. If this is not possible, bury, chip or carefully seal wood from infected oaks under thick plastic. The plastic must cover the entire wood pile with the edges buried in soil to prevent beetle access. Once the wood is dry and the bark is loose or fallen off (about one year), it is no longer a source of infection.

Steps to take when oak wilt is suspected

A plastic tarp tightly covers wood from a tree killed by oak wilt. Photo by Julie Stachecki.

If oak wilt is suspected, take immediate action to get a positive diagnosis. Send a sample of a symptomatic branch to MSU Plant & Pest Diagnostics to confirm oak wilt unless a mycelial mat is discovered on a dead oak. If you find a mycelial mat on a dead oak—normally visible beneath a bark crack—that is sufficient for positive diagnosis. Once a positive diagnosis is obtained, consult a professional trained in oak wilt management as soon as possible. This disease will continue to spread unless management techniques are begun promptly.

Additional resources

More information and a free downloadable field guide to Michigan oaks: www.MichiganOakWilt.org


For more information on a wide variety of Smart Gardening topics, visit www.migarden.msu.edu or call MSU’s Lawn and Garden hotline at 1-888-678-3464.


Published August 2019. This publication is supported in part by the Crop Protection and Pest Management Program 2017-70006-27175 from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.


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This article was published by Michigan State University Extension. For more information, visit http://www.msue.msu.edu. To have a digest of information delivered straight to your email inbox, visit http://www.msue.msu.edu/newsletters. To contact an expert in your area, visit http://expert.msue.msu.edu, or call 888-MSUE4MI (888-678-3464).

Smart Gardening Starts Now

Area Education, How-To's, Recreation, , ,

Metro Health and MSU Extension present ‘Gardening 101’

Any one who’s tried it knows that the beauty of gardening is seeing your hard work pay off with a bounty of colorful blooms or freshjanice_limbaugh vegetables for the dinner table. Whether your green thumb is seasoned or just slightly tinted, a successful growing season starts now with Smart Gardening.

What’s so smart about Smart Gardening as compared to ordinary gardening?

“Balance!” says Rebecca Finneran, a 28-year horticulture educator with the Michigan State University Extension program.

“We create so many of our own problems with too much or too little watering, using too many chemicals and not understanding our soil.

“What’s smart is understanding what does the plant needs and then try to adjust our behaviors so that it fits with the plant’s – that’s Smart Gardening,” Finneran told a room full of local gardeners at a free “Gardening 101′ seminar hosted by Live Healthy at the Metro Health Conference Center.

It’s a ‘ground-breaking’ idea that the MSU Extension team put into action about three years ago, educating the public on how to be environmentally savvy when planning, preparing and maintaining your vegetable garden. Smart Gardening, explains Finneran, “has long been a hallmark of what  we do [at MSU]. We help people connect with the real world of horticulture and to do that in an environmentally healthy way to save time, money and energy.”

The ‘Gardening 101’ seminars run about an hour and half. During that time, participants get an overview of Smart Gardening techniques such as preparing the soil, how to reduce the chemical input of both fertilizers and pesticides, how to determine the size and location of the garden, deciding what variety of plants to grow and the best way to water it all. And because vegetable gardens are as unique as the individual gardener, there and many creative options to consider when planning it out.

Yet before any plans are drawn, soil tilled or seeds planted, Finneran’s first words to the wise gardeners is to be realistic. For the new gardener, she suggests starting small.

“Too many times gardeners get over excited at the start of the season and plant too much. Then by July, what happens? You want to go on vacation but who’ll take care of the garden? It’s too hot, there’s too many mosquitoes and taking care of a garden is just dreadful. So you let it go. Then you’re ashamed of it.”

She suggests considering sharing a common gardening space with neighbors, community groups or coworkers.

“I did this with a group of my coworkers. We wanted a little vegetable garden at work. So we each worked one lunch hour per week, about 30 minute five days a week. And guess what?” Finneran asked the crowd. “Many hands made light work! We had a nice crop of vegetables every day for lunch.”

Although she is an ornamental horticulturist with a background in landscape design, Finneran grew up with a farm background and had vegetable gardens all her life. As a result and over time, she creates vegetable gardens that look like masterpieces!

“Vegetable gardens can be useful and beautiful. I think that’s an important thing to consider. There’s no reason we can’t enjoy our vegetable gardens regardless of their size and usefulness. How you plan it out is something to think about,” she suggests.

LOCATION! LOCATION! LOCATION!

When it comes to having a successful garden, it’s all about location! First and foremost, Finneran says, is to consider the accessibility to a water source. “You won’t want to be lugging 90 feet of house across the yard on a 90 degree day,” she points out. With that said, your garden location may be as close as your patio or deck. Whether you’re picking fresh vegetables from a garden out in the yard or a patio container, it’s still rewarding.  Here are some tips to consider when choosing a ‘smart site’ for your garden:

* Convenient your home and close to a water source.

* Where the soil is good and free from toxins.

* Sunny, level spot (eight to 10 hours of sunlight depending on the vegetable).

*Avoid north-facing slopes and low areas.

*Stay away from trees and shrubs.

“We really miscalculate this one a lot,” Finneran points out. “Where’s the neighbor’s tree going to be casting its shadow by August?” She suggests to consider the garden’s location over the course of time.

“Think about it and then plant early harvest plants in the areas where shade will dominate from August on. Plant your later harvest plants on garden’s edge where there’s more sunlight on a daily basis,” she says.

Don’t Guess – Soil Test!

There’s more to having healthy soil than earthworms. In fact, it’s mostly about things we cannot see. Understanding how these components all work together is known as soil biology and it’s considered the new frontier of science and the gardening world.

“Have you ever hear of the term soil biology?” Finneran asks. “We hardly every think of soil as being a living, breathing thing. It’s either sand, silt or clay and you walk around on it. But in fact there are billions of micro-organisms that live in your soil. The way they live together is they consume each other and eat the organic matter. They are the ones responsible for releasing the nutrients that the plants need.

“These micro-organisms have an amazing, living, reciprocity with the plant root to allow it to have the nutrients that it needs to live. So if there is a reduced living component, plants are not going to do so well.”

Before the first seed is planted, Finneran encourages getting the soil analyzed by the Michigan State University Extension to determine the nutrients needed in your garden as well as the pH and organic content of the soil. Soil test kits can be purchased online at the MSU Extension Bookstore (search for E3154), or your local MSU Extension office. The kits come with a postage-paid mailer and a re-closable plastic bag to fill with a soil sample. The postage-paid mailer can be placed in  your mailbox for pick up and sent to MSU for analysis. The results take up to two weeks and will tell you what amendments to make and in what proportions to add for the best results in the vegetable garden.  A Smart Garden starts with a healthy soil and to achieve that:

*Add organic matter to your soil every year.

*Only add the recommended amounts of fertilizer based on the soil test results. Over application of phosphorus and nitrogen fertilizers is a known contaminant of surface and ground water.

*Prepare your garden soil for planting by tilling (lightly) to break apart aggregates and mix in organic matter. “The less manipulation, the better,” says Finneran.

MSU Extension offers the community a wealth of free information on horticulture. For more information on Smart Gardening, including helpful articles, videos, classes and events, visit www.migarden.msu.edu. For more information on other topics, or to contact an expert in your area visit www.msue.msu.edu or call the toll free hotline Monday through Friday 9:00 a.m. to noon and 1:00 p.m. to 4:00 p.m. at 1-888-678-3463.