Phytophthora Graphic Link

Plant Destroyers Poster

Intro to Plant Pathogens

Plant pathogens are microscopic organisms that cause disease in plants. They kill billions of plants each year! Some pathogens can infect many plant species (generalists), where others can only infect certain species (host specific). These organisms cause problems in agriculture and natural environments such as native forests and grasslands. Below are a few examples of diseases caused by plant pathogens.

Western Gall RustBlueberry Mummy BerryWheat Stripe Rust
Western Gall RustBlueberry Mummy BerryWheat Stripe Rust

Billions of rands are spent every year trying to control plant diseases. Plant pathogens threaten food security and the health of natural systems such as the fynbos or the native forests of South Africa. They also cause problems in plantations, ultimately increasing the cost of wood products.

Plant Destroyers

Phytophthora (pronounced Fy-TOFF-thor-uh) is a group of plant pathogens that are famous because of the dramatic disease outbreaks they cause. The word Phytophthora translates into 'plant destroyer' from Greek.


phyto = plant
phthora = destroyer

Phytophthora infestans

Perhaps the most well known species is Phytophthora infestans, the species that is responsible for the Irish Potato Famine. P. infestans causes a disease in potatoes referred to as late blight. It can also infect tomatoes and even petunia hybrids. This species is present in South Africa, still causing problems more than a century after the Irish Potato Famine.

Blight Potato

Potato (Solanum tuberosum): Late blight, caused by Phytophthora infestans

Image Source: USDA, flickr.comImage Source: Scott Nelson,

Phytophthora ramorum

Another Phytophthora species of concern is P. ramorum. This species is responsible for Sudden Oak Death in North America and Ramorum Disease in the United Kingdom. It has killed millions of oak trees in the North America and entire landscapes of Japanese larch have been removed to control the spread in the United Kingdom.

Landscape of Dead Tanoak TreesLesion on a Rhododendron
Dead Tanoak Canopy

More information about P. ramorum is presented in the below videos. Check them out!

Phytophthora ramorum is a generalist pathogen. It can infect more than a hundred different species of plants and it has practically eliminated mature tanoaks from the landscape in infected areas of California and Oregon, USA. If this species is allowed to spread to the fynbos, the consequences could be devastating!

Phytophthora ramorum, growing in v8 agar

Phytophthora cinnamomi

Finally, the last plant destroyer presented in this blog is Phytophthora cinnamomi—saving the best (or worst) for last! P. cinnamomi was originally described causing disease in cinnamon trees, hence its name. This species is also a generalist pathogen, causing root rot of many plants. It has been suggested to be the most ubiquitous Phytophthora species on the planet. It can infect thousands of plant species!

Phytophthora cinnamomi is present in the fynbos and has been implicated as the cause of root rot of many Proteaceae species. If you see a dying plant in the fynbos, there is a good chance P. cinnamomi is involved. However, despite knowing it is present, there is a lot that we don't know about it!

For example, we do not know:

  • where it is and where it is not
  • where it came from
  • which species it infects and how it is affecting the biodiversity of the fynbos
  • how it will respond to a changing climate
  • how it affects regeneration after a fire
  • its role in the decline of the silver tree near Table Mountain

    There is a lot to investigate! and you are invited to conduct the research with us!

    Start by contacting us!