Emerald ash borer, Japanese beetles, bush honeysuckle, purple loosestrife, chestnut blight. These listed items are all types of invasive species, which have dramatically altered our landscape. An invasive species can be a non-native insect, plant, disease, or animal that causes environmental damage, economic harm, or impacts human health in a negative way. Those pests listed above is just a highlight of a growing list of invasive species that threaten the stability of our native ecosystems and developed landscapes.
It may not come as a surprise that I am back, taking up valuable digital space to tell you of another potentially devastating non-native disease that attacks oak trees – Sudden Oak Death or Phytophthora ramorum. The name Phytophthora (Fie-TOF-ther-uh) means "plant destroyer" and is a family of water mold fungi that has played a major role in human history. Remember the Irish Potato Famine of the 1840s? That was Phytophthora infestans, commonly known as potato late blight.
Phytophthora ramorum or P. ramorum is known to infect over 30 different plant species including witch hazel, viburnums, horse chestnut, lilacs, and rhododendrons. When these plants are infected the disease is called Ramorum Blight and it may not be fatal but will cause bark cankers, leaf spots, and twig dieback. When oaks are infected with P. ramorum it is termed Sudden Oak Death, because, for several oak species, this disease will quickly kill the tree.
P. ramorum has ravaged West Coast forests attacking seven different species of oak. Leaving behind barren vistas of dead trees.
You may be thinking, "At least this disease is way over in California and not in Illinois." Unfortunately, the Illinois Department of Agriculture has confirmed P. ramorum throughout the state on infected plant material at big box garden centers. Macomb, Illinois is one of those locations that had plants confirmed with P. ramorum.
How did it get here? Most of the landscape plants we purchase at garden centers are grown on the West Coast. Regulators monitor growers to make sure a disease like P. ramorum doesn't spread across the country, but often with these things, it is only a matter of time before a mistake occurs and the disease is able to spread.
To date in Illinois, the only infected plant material that tested positive for P. ramorum are rhododendrons and lilacs sold at Walmart, HyVee, and Rural King in 2019. If you purchased these plants and are seeing signs of Ramorum Blight (dark brown spots on leaves or branch tips) contact Illinois Department of Ag or your local Extension office for guidance. Officials do not want people to dispose of these plants in compost or landfills where the disease could spread.
There is no reason to panic, as this disease hasn't been found in any of our native oaks yet. We even aren't quite sure which species of oak would be more at risk or if any would be resistant. Based on the oaks infected out west, it is thought that northern red oak and pin oak may be more susceptible. Until Sudden Oak Death is confirmed in your local area, there is no reason to pursue treatment of your oak trees.
Some good news – Just because P. ramorum thrives on the West Coast, does not mean it will succeed in the Midwest. There are many factors of our Illinois climate that could prevent this disease from establishing. We can grow a lot here in Central Illinois. Hopefully, the disease Sudden Oak Death isn't one of them.
Good Growing Tip of the Week: The plant pathogen that causes Sudden Oak Death has been found in 10 counties throughout Illinois. Contact your local Extension office if you purchased rhododendrons or lilacs from HyVee, Walmart, or Rural King in 2019.