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 in particular trees can have, the most dangerous is the oomycete Phytophthora ramorum .
But why do we have to worry? Because it is the pathogen that was behind the death of numerous oaks of the Lithocarpus densiflorus species in California in 1995. In addition, it affects other species that are widely cultivated in temperate regions, such as Acer palmatum , known as maple Japanese.
What is it and what are its characteristics?
Image – Flickr / R6, State & Private Forestry, Forest Health Protection
The Phytophthora ramorum is a oomiceto parasite that causes what is known as sudden oak death, but affects many other plant species as we shall see below. It occurs in the form of mycelium , causing 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 oomicetos of the genus Phytophthora media like where moisture remains high, either the substrate of a plant grown in pots, or soil in which grow 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 the humidity 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?
Image – Wikimedia / 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:
- Abies grandis (large fir)
- Abies procera
- Acer palmatum (Japanese maple)
- Aesculus hippocastanum (horse chestnut)
- Arbutus (strawberry tree)
- Camellia
- Castanea sativa ( chestnut )
- Fagus sylvatica (beech)
- Larix kaempferi (larch)
- Lonicera (honeysuckle)
- Magnolia
- Picea sitchensis (Sitka fir)
- Pieris
- Pseudotsuga menziesii (Douglas fir)
- All oaks of the genus Quercus, especially Quercus robur , Quercus ilex, Quercus petraea, Quercus cerris and Quercus rubra
- Viburnum
What are the symptoms and damage it causes?
These:
- Chancres on the trunk
- Stem necrosis
- Dark (or black, depending on the plant) spots on leaves
- Premature leaf fall
- And finally death
What does the treatment consist of?
Image – Wikimedia / Karel Černý
On the one hand, you have to cut the affected parts and, if possible, burn them or throw them 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 Phytopthora ramorum , Fosetil-Al (Aliette) is used, which you can buy here , although it must be borne in mind that the disease will not be completely eliminated, so treatments must be carried out several times a year.
Another thing to do is make sure the soil and pot drainage is good , and take action if it isn’t. 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 infection , starting with buying healthy plants, and going through keeping them well cared for. This means that in case of having them in containers, they must be provided with a substrate that is new (that is, one that has not been used before), a clean and disinfected pot, and also they must be placed 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 that of solarization , which consists of covering the soil 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 soil. ground. After the season, the plastic is removed and we proceed to planting.
But apart from that, it is also important to make sure that the acquired plants are healthy , without stains or pests, and that their needs are known to give them the care they require.
