Phytophthora: how to prevent and cure this disease

Although we have many tools in agriculture and gardening to combat pests and diseases, the Phytophthora fungus is one of the biggest problems and headaches of modern agronomy.

A very resistant fungus, capable of behaving differently depending on the soil, temperature and oxygen conditions, affects an increasing number of plants, and its eradication is tremendously complicated.

Ecological agriculture advances unstoppably conquering the market of many crops, hence prevention practices are recommended as opposed to curing, since for the control of Phytophthora  there are or almost no tools in ecological, except copper.


Phytophthora is a genus of entomopathogenic fungi very present in intensive agriculture and widespread throughout the world. The persistence and its difficult eradication makes it one of the worst diseases in most crops.

One of the worst determining factors is the great survival capacity of the Phytophthora fungus , being able to live in the soil for several years, until it is activated in the presence of humidity and favorable temperatures.

In a situation of high humidity, typical of the months of greater rainfall or a carelessness with the frequency and volume of irrigation, the fungus advances unstoppably, penetrating through the root and occupying the vascular bundles. Once it is installed in the plant, it produces a dizzying wilting that kills the plant after a few days.

The rapidity of its action is usual since it prevents the free circulation of the sap , which is why there is a rapid withering of the aerial part of the plant. Hence, in some crops it is known as “dry” or “blight”.


Each crop is affected differently, especially since it is often not carried out by the same Phytophthora species , although the genus does. However, there are specific and characteristic symptoms in most crops, such as the following:

  • Symptom of dry leaves, even if there is enough moisture in the substrate or soil.
  • Color change, often with brown or brown colors and yellowing in horticultural and ornamental.
  • The first symptoms are observed on the leaves, and then on whole stems or branches.
  • Dark spots appear on the stem and on the neck of the plant, often called cankers, and the appearance of gums is also common.


As we said at the beginning, when we speak of Phytophthora  we mention the genus of fungi , of which several species have been described. It is well known in tomatoes, characterized as tomato mildew  ( Phytophthora infestans ), one of the species that most affects all types of crops.

The most important species are the following:

  • P.cinnamomi
  • P. palmivora
  • P. citrophthora
  • P. parasitica
  • P. arecae
  • P. cambivora
  • P. capsici
  • P. colocasiae
  • P. cryptogea
  • P. drechsleri
  • P. infest
  • P. meadii
  • Mexican P.

However, there are a few more that we will mention below.


Phytophthora in tomato cultivation. Source:

This species of the phytophthora genus is the cause of one of the best known tomato diseases , generically known as mildew or late blight.

This disease usually appears in tomato crops from spring, with rising temperatures from 15 to 23 ºC, especially from heavy rains that increase the humidity above 75-80%.

The biggest problem with this disease is that it has a great resistance , being able to remain inactive in the soil for years, waiting for the new planting and the increase in humidity.

On the other hand, its dissemination is quite easy , either through cutting tools or even by water or wind.

Symptoms in tomato

Tomato mildew creates brown or brownish spots on leaves, with a moist, rot-related touch. On the underside of the leaf you can see a whitish powder that should not be confused with powdery mildew.


Source: GMR Canarias

This species of phytophthora is typical of many tree crops, especially avocado . It is the fungus responsible for the disease known as avocado root rot , one of the most common and causing the most economic damage in any growing area of ​​this subtropical.

The fungus has a great capacity for survival and attacks the roots with great virulence, destroying them in a few months. The most serious cases end with the complete death of the tree.

Symptoms in avocado

The first observations of the disease in the avocado crop are made on the leaves. It exhibits a rapid withering with a color change to brown, progressing downwards.

Then the side branches start to dry out due to the blockage of sap circulation. There is less sprouting and the leaves tend to be smaller, a sign of an energy deficit in the plant caused by less and less root development.

Read more: information about the disease in avocado


Phytophthora in pepper cultivation. Source: Koppert biological systems

The fungus scientifically known as Phytophthora capsici is present in another solanaceous plant such as the pepper and all chili peppers.

The disease is known as pepper blight, and it appears with temperatures and humidity similar to those required in tomato cultivation. Conditions of high humidity, low soil oxygenation and rising temperatures make the crop quickly become infected.

The symptoms are somewhat different from those of the tomato crop. Phytophthora capsici causes stem rot , specifically the root neck.

At the microscope level, what causes is a blockage of the channels that transport the sap and the water towards the upper part, this drying up in a few days and causing a very visible wilting.

Work to prevent the disease in pepper

This disease has a difficult solution, so it is recommended to carry out prevention tasks such as the following:

  • Wash and disinfect all used agricultural machinery, such as scissors, knives or ropes.
  • Remove residue from affected leaves and stems.
  • Choose varieties that are more tolerant or resistant to the disease.
  • Ensure good ventilation of the crop.
  • Increase soil drainage and avoid very clay soils.
  • Periodically disinfect the irrigation water or the pond.


Symptoms of Phytophthora in citrus. Source: IVIA

There are several species of fungi that cause rot and gum disease in citrus fruits. In general, they are caused by several species of Phytophthora, the most common being P. citrophthora.

In soils with poor drainage or prone to waterlogging, the presence of this disease is common, especially in conditions above 18ºC. In general, the infection process is slow and the first symptoms are observed after several months from the beginning.


There are various active ingredients for the control and prevention of the disease. Some of these bases are usable in organic farming, especially copper formulations such as copper oxychloride , hydroxide, Bordeaux mixture and organisms such as Trichoderma .


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