Phytophthora ramorum: symptoms and treatment

Phytopthora ramorum is a dangerous plant pathogen

Image – Flickr / R6, State & Private Forestry, Forest Health ProtectionSe

From the first second of life, plants have to manage to survive multiple insects and microorganisms eager to feed on them, regardless of whether they are part of a jungle or a garden. Of all the enemies that woody species and trees in particular can have, the most dangerous is the oomycete Phytophthora ramus.

But Why do we have to worry? Because it is the pathogen that was behind the death of numerous oaks of the species Lithocarpus densiflorus in California in 1995. In addition, it affects other species that are widely cultivated in temperate regions, such as the Maple palmateknown as Japanese maple.

What is it and what are its characteristics?

Sudden oak death is a diseaseSudden oak death is a disease

Image – Flickr / R6, State & Private Forestry, Forest Health Protection

The Phytophthora ramus It is a parasitic oomycete that causes what is known as sudden oak death, although it affects many other species of plants as we will see below. It comes in the form of myceliumcausing symptoms and damage that are often fatal to affected plants.

Because of this, the European Union has been trying since 2002 to prevent it from dispersing, but unfortunately its efforts are not yielding the expected results. That same year, it was detected for the first time on the island of Mallorca (Balearic Islands, Spain), and later it was also detected in parts of the Iberian Peninsula (Badajoz, Asturias, Galicia). In addition, it is present in many other European countries, including Germany, France, Italy and Sweden; And we cannot forget the United States, where it wreaks havoc in California and Oregon.

How is it transmitted?

At oomycetes of the genus Phytopthora they like environments in which humidity is kept high, be it the substrate of a plant that is grown in a pot, or the soil in which it grows in the garden. This humidity can be excessive when watering a lot or after an abundant rain, but also when that soil or substrate is very compact, since it costs them more both to absorb moisture and to lose it.

But if we add to that the stress that the plant may be suffering, be it due to excess water, high temperatures, improper pruning, or a transplant done at a time that is not correct (remember that transplants are done at late winter, or well into spring if they are plants of tropical origin, such as those that are often grown indoors), we can be sure that they will do everything possible to infect it, and P. ramorum will do so by entering through the roots or a pruning wound.

What species does it affect?

Trees die with phytopthora ramorumTrees die with phytopthora ramorum

Image – Wikimedia Commons / Joseph O’Brien, USDA Forest Service

According to a UK portal, it is estimated that more than 150 species of plants are victims of Phytopthora ramorum, including:

  • great abies (large for)
  • You will be tall
  • Maple palmate (Japanese maple)
  • Aesculus hippocastanus (horse chestnut)
  • Arbutus (strawberry tree)
  • Camellia
  • castanea sativa (brown)
  • Fagus sylvatica (is)
  • Larch kaempferi (larch)
  • Lonicera (honeysuckle)
  • Magnolia
  • Picea sitchensis (Sitka for)
  • Pieris
  • Pseudotsuga menziesii (Douglas for)
  • All oaks of the genus Quercus, especially Oak, The holly oak, the petrified oak, the cherry oak y quercus rubra
  • Viburnum

What are the symptoms and damage it causes?


  • Chancres on the trunk
  • Stem necrosis
  • Dark (or black, depending on the plant) spots on leaves
  • Premature leaf fall
  • And finally death

What is the treatment?

Pieris japonica is a shrub susceptible to phytopthoraPieris japonica is a shrub susceptible to phytopthora

Image – Wikimedia / Karel Černý

On one hand, the affected parts must be cut and, if possible, burned or thrown away (Being a pathogenic oomycete and highly contagious between plants, the removed parts should NOT be thrown into compost or garden soil). If they are plants that are in pots, they will be taken to an area far from the others, to minimize the risk of contagion.

In addition, they must be treated with fungicides. Yes, we have said that they are not fungi, but fungal treatments are also valid for oomycetes. Specifically, for the Phytophthora ramus the Fosetil-Al (Aliette) that you can buy is used here!Although it must be borne in mind that the disease is not going to be completely eliminated, so it is necessary to carry out treatments several times a year.

Another thing to do is make sure the soil and pot drainage is goodand take action if it is not. For example, if when watering or raining puddles form on the ground that take hours or even days to disappear, it is necessary to install drainage pipes, make slopes or put sewers so that excess water can continue its way without endangering the plants.

If they are in pots, it is crucial that they have holes in their base. Likewise, the substrate to be used has to be light, and absorb and filter water quickly.

It can be avoided?

Not really, not at all. But what is possible is to reduce the risk of infectionstarting with buying healthy plants, and going through keeping them well cared for. This means that if you have them in containers you have to provide them with a substrate that is new (that is, one that has not been used before), a clean and disinfected pot, and also you have to place them in a place where they will be well, having consider your light needs.

In the case that they are kept in the ground, it is best to carry out disinfection treatments before planting them. A natural and effective method is the solarization, which consists of covering the ground with transparent polyethylene plastic, preferably in summer, after having passed the tiller and having broken up any clods that may have formed, and then leveling the ground. After the season, the plastic is removed and we proceed to planting.

But other than that it is also important to make sure that the acquired plants are healthywithout stains or pests, and that their needs are known to give them the care they require.


  • Forest health of the Balearic Islands. Web.
  • Forest Research (UK). Web.

Phytophthora ramorum: symptoms and treatment

Leave a Reply

Scroll to top
%d bloggers like this: