Alert: Sudden Oak death

Friday, June 7, 2019
Bob Bruner

In late May, the Department of Natural Resources released an alert on species of rhododendron. These plants are popular ornamentals; unfortunately, the also are carriers for Phytophthora ramorum, or Sudden Oak Death, as it is commonly known. In an area such as ours, covered in hardwoods, this disease is a real threat that cannot be taken lightly.

According to Janna Beckerman, Purdue University, the pathogen that causes this disease acts in similar ways to the fungi, but does not belong to the same group of organisms. This pathogen is able to spread through moisture, but is capable to surviving in dry conditions due to think cell walls. Since this isnít a fungus, it also means that normal fungicidal treatments are not effective.

Of the 17 species of oak in Indiana, the black, blackjack, cherrybark, Northern pin, pin, red, scarlet, and Shumard oaks are susceptible to this disease. Signs of infection include, at least in red oaks, oozing sap and red-brown cankers. This disease is very lethal to susceptible species, and death is often a consequence of infection.

One of the most problematic traits of this disease is its ability to infect of species outside of oak, particularly foliar hosts. These plants include rhododendrons, azalea, bivurnum, lilac, and periwinkle. Itís rare to not see these plants place in yards and gardens throughout our state. Infected hosts may have tissue that looks like it has experienced sunscald or dieback, but it rarely is lethal. This makes infected hosts a perfect breeding ground for the spores that allow this disease to spread.

The Indiana Department of Natural Resources has identified several rhododendrons sold at Rural Kings and Walmarts throughout the state. Initial numbers said at least 30 stores has infected plants, but estimates may place that at a number several times higher.

According to Dr. Beckerman, this disease is brand new to Indiana, and thus there is no way to predict how it will interact with our environment. It is most dangerous at the urban-forest interface, so if you live in an area such as this, you will need to be watchful for what you buy and plant. If you believe you have an infected plant, take all precautions to prevent contamination. Double-bag the plant and destroy it by throwing it in the garbage. Sanitize all garden tools and clothing.

All of this information and more can be found on Purdueís Department of Agriculture website, https://ag.purdue.edu. You can also contact your local ANR Extension Educator, Bob Bruner, at 812-448-9041, 812-829-9041, or rfbruner@purdue.edu. Purdue University is an equal opportunity/equal access/affirmative access institution.

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