Fighting Phytophthora at Sheffield Park

Rhododendrons under threat from Phytopthera Ramorum

The disease Phytophthora ramorum, also known as sudden oak death, spread to the UK in 2002. It was first detected in the USA in 2001, affecting their (Tan) wild oak trees, hence the name. Luckily it doesn’t affect our English oaks; however it does affect many of the trees and shrubs we know and love such as rhododendrons, camellias and many more.

What is Phytophthora ramorum

Phytophthora ramorum is a fungus-like organism that attacks a range of native and non-native trees and shrubs. The spores spread from infected plants to healthy plants and are washed into soil and leaf matter where they are spread on footwear and the feet of animals. Moving or cutting infected plants to unaffected areas can also spread spores.

How has it affected us here at Sheffield Park and Garden?

Since May 2010, we have had known instances of Phytophthora ramorum breaking out in different parts of the garden, probably brought into the garden on footwear or the feet of animals. We are working with the government agency FERA to contain these outbreaks and prevent further spread of the disease both within the garden and outside of the garden boundary.
So far the only two species that the disease has affected in our garden are Rhododendron ponticum and Kalmia latifolia; however it is estimated that up to 65% of our plant collection here at Sheffield Park could be susceptible to the disease.

What are the symptoms and how are we dealing with it?

The symptoms specific to the rhododendrons at Sheffield Park and Garden, include blackening of leaves at the midrib and tip and wilting and die-back of shoots.
There are several ways that FERA recommends dealing with the disease including stem injection of herbicides and application of herbicides to cut stumps. We have chosen, to remove the infected shrubs completely, burning the infected material in situ wherever possible as this is the best method of eradicating the disease by not moving infecting material around the garden. We are using this as an opportunity to clear some areas of the garden, opening up historic vistas and allowing for replanting of non-susceptible species.
We have lifted the skirts and crowns of Rhododendrons and other susceptible species around the path network. This is to help prevent the disease, which we believe to being spread by foot on the path network, spreading by rain splash. By crown lifting we also are allowing better air movement though the plants and not letting the disease thrive in humid conditions under the plants.