Learn how to prevent and treat the most common diseases and parasites of the organic garden

Pests and diseases in the ecological urban garden are usually one of the main concerns of market gardeners. And if you are among them, surely you know very well what I mean. In this article you have very useful information to prevent them and treat them in an ecological way.

We also advise you which organic seeds to use , the best planters, growing boxes and tables for your garden and essential books to learn everything about organic gardening .

The appearance of discoloration spots or small holes in the leaves and fruits , reflects an imbalance in the garden, with the presence of diseases that affect the production of the plants we grow.

It is very common, although no less discouraging, but it really depends on many variables and not all diseases can be treated in the same way , just as treatment with the application of products may not be enough and more profound changes are required.

As a first step, we will have to consider the garden as an ecosystem or agrosystem , therefore the diseases that we can find there are related to some failure in its balance.

Although here we refer to urban or peri-urban orchards for self-consumption, the concept applies – and is increasingly assumed – to all agrosystems. From organic farming , the garden itself has the necessary tools to develop preventive techniques against pests and diseases and leave the direct fight as a last resort.

In this sense, an attempt is made to strengthen the defenses of the plants and not eliminate parasites, since these do not represent a threat in themselves, but rather the combined result of an immune deficiency in the plant and an imbalance in the environment.

Thus, bio-products and bio – preparations , whose production can even be done at home, help control populations of microorganisms , as well as to fight diseases effectively when they occur.

> Lee: What can you grow on a Grow Table ?

Phytopathology and plant diseases

Plant diseases are the object of study in phytopathology, an applied science integrating knowledge from other disciplines that deals with the nature, cause, control and other aspects of disease . .

The nature of crop diseases depends on both:

  • The causal agents : which are usually molecular entities, such as viruses, or microorganisms, such as bacteria, fungi, oomycetes, nematodes, protozoa and even other plants; like,
  • Interactions : which are modulated by components of the environment, involving biochemical, physiological, genetic and molecular processes configured according to abiotic elements of the soil (such as O2 concentration, physical structure, temperature, pH, salinity, etc.) and the air environment (humidification, lighting, temperature, etc.).

Diseases can occur both in agricultural crops and in wild plant communities, only in the first case it can have devastating socio-economic effects.

urban garden pests

5 most common diseases in the organic urban garden

  1. Mites

They are a subclass of arachnids of very small dimensions (a few millimeters long), and can be found throughout the plant, both leaves, stems and fruits . There are about 50,000 described species, although there are still many more to be identified, and among the most frequent is the Red Spider ( Tetranychus urticae ).

¿ What are the symptoms of a plague of mites ? The “red spider” feeds on the sap of plants, causing discoloration and desiccation in both leaves and fruits, with whitish and yellowish spots being the main symptom of the presence of this mite. .

Prevention of mite pests:

  • Eliminate the remains of previous harvests or pruning, especially if the presence of mites is suspected.
  • Fertilize the harvest to ensure greater resistance, avoiding excess nitrogen that favors this pest because it provides more turgor to the vegetables.
  • Maintain a good ambient humidity and spray the leaf on the underside, the spider mite is favored by the dry and hot environment, the humidity can help to reduce its colonies.


  • A natural predator of mites is another mite, Phytoseiulus persimilis , as well as other predatory microorganisms.
  • Garlic extract, which has a repellent action and helps fight the plague by using it in combination with another product that acts by ingestion or contact.
  • Potassium soap, which acts by contact, so the plant must be wetted well.
  • Neem oil, as it is ovicidal and larvicidal.

The products are always applied when there is little solar incidence (since the light degrades the products) and on the underside of the leaves.

  1. Mealybugs

They are terrestrial crustaceans that feed on tender and juicy plant organs. It is estimated that there are more than 8,000 species, some have bodies formed by scaled rings that allow them to become a ball, others remain fixed to the plants forming a kind of shell.

In a first stage, they develop in a mobile phase and then attach to plants to feed on them. There are three groups of these terrestrial crustaceans that usually occur in orchards: the pseudococci, the lecanines and the diaspines.

¿ What symptoms have plants suffering from cochineal plague ? The symptoms of damage caused by mealybugs are distinguished by a weakening of the plant and, in some species, the most common is infection by fungi that settle in the honeydew produced by the shells. .


  • Reduce excess humidity and shade, as it is the preferred environment for these species.
  • Remove excess vegetation and pruning remains.
  • Control excess nitrogen in the compost.


  • Although the best technique is to minimize the conditions that favor their presence, the next safest treatment for the plant is to remove the shell manually, since most of them are perceptible.
  • Potassium soap has the property of softening the exoskeleton and weakening them.
  • The most effective natural predators are ladybugs or vaquitas.

Mealybugs usually settle in the shady and humid parts of the stems and the underside of the leaves, so that is where the products must be controlled and applied for their elimination.

  1. White fly

It is a small insect, 3 millimeters long, that feed on the sap in the leaves of plants. There are different species, native to tropical areas but spread throughout the world. The best known affect fruits ( Aleurothrixus floccosus ) and cabbages ( Aleyrodes proletella ).

¿ What are the symptoms of whitefly pests ? The presence of these flies is noticed when shaking the plant, when they are seen flying like a cloud of white dust. The first symptoms are also distinguished in the weakening of the plant, but when the infection is very intense, a white mealy substance is distinguished on the underside of the leaves. At the same time, the soft fly injects toxic saliva into the plant and produces a honeydew that stains leaves and fruits, known as bold .


  • To control its appearance, it is important to control weeds, which is where this fly tends to take refuge.
  • Interlayer aromatics such as Chinese carnations, marigolds or ornamental tobacco, which have a repellent effect against whiteflies.


  • Water with mild soap, to spray the plant and control the proliferation.
  • Infusion of tansy, retonona or piratrina.
  • Natural predators, such as the small wasp Cales noacki and the Encarsia formosa .

The flies deposit their larvae on the underside of the leaves , in the early stages it can be almost imperceptible, so it is important to spray the products in that area to control their reproduction.

  1. Aphid

There are many types of aphids, they inhabit the entire planet and are present in all gardens and orchards. Some affect only a specific plant, others are polyphagous.

¿ What symptoms show plants with aphid infestation ? The main symptoms are identified by seeing the insect, which can measure about 3 millimeters, or by yellow or pale green spots on leaves and stems. The presence of aphids can also be seen by sprouts or rolled and sticky leaves, as well as by the appearance of the Black fungus ( Fumaginas sp.), Black in color, and ants , which settle to collect the honeydew excreted by aphids.

The Negrilla fungus prevents photosynthesis, so the deterioration of the plant is quickly appreciated, and it is the aphid itself that quickly spreads it to other plants.

> Read: the 15 best Ecological Remedies against Aphid .


  • Eliminate weeds and pruning debris, where they tend to take refuge.
  • If you think there may be an attack, remove the damaged leaves.
  • Plant interspersed species such as rose bush, honeysuckle, lupine, foxglove and nettle that act as repellants.


  • Natural predators, such as ladybugs, small wasps, and lacewing.
  • Spray the plant with soapy water, prepared with 2 tablespoons of neutral soap flakes and 2 tablespoons of 90 ° alcohol.
  • Infusion of nettles.
  • Neem oil.
  • Garlic extract.
  • Potstic soap.

The aphids also settle on the underside of the leaves, so the treatment with products should be done mainly on this sector.

  1. Nematodes

They are tiny worms (barely 0.2 millimeter) with an unpigmented body that pierce plant cells, destroying the vitality of the plant.

They live in moist soils and spread easily through soil, plant debris, and farm implements. There are several genera that affect different types of plantations, they live especially in sandy soils, hot conditions and abundant irrigation, being very sensitive to changes or the lack of crops.

It is important to note that nematodes are in all soils, which varies their appearance as a disease in the garden is associated with the amount of these and the sensitivity of the plants.

How do you know that crops are plagued by nematodes ? It is very difficult to distinguish if the plant is being attacked by nematodes, first because the attack occurs at the root and, on the other hand, because the symptoms can be confused with excess or lack of water, as well as a lack of nutrients. .


  • Disinfecting the land before sowing, although it is a process that is usually applied to commercial crops, if there is full security of previous crops affected by nematodes, it can be done by solarization *.

* It is carried out in summer, tilling and with abundant watering beforehand (that will heat up to 40 cm), to later cover it with a thin transparent plastic (polyethylene between 100 and 200 gauges thick). This sheet should be taut and with the edges perfectly buried so that the heat does not escape for about 4 to 6 weeks.

The treatment of nematodes is very complex, as it is difficult to identify them in the aerial part of the plant. The affected plants must be completely removed and the best treatment is disinfection and tillage, aerating the land, before sowing.

However, and apart from the treatments with biopreparations, it is essential to consider again that the diseases are caused by some failure in the system, so it is essential to assume a good planning of the garden , the rotation of crops, as well as the species , fertilizers and irrigation suitable for the specific environmental conditions of the orchard.


  • “Plant diseases: impacts, threats and control”, Rafael M. Jiménez-Diaz. Bulletin of the Royal Academy of Córdoba. 2017.
  • “Los mites”, JA Martín armas. NaturalBio.
  • “Red spider control and prevention”, Certis.
  • “Plagues and diseases of plants”, Antonio Jesús Zapata Sierra. University of Almería.
  • Common garden pests. Identification and integrated management ”, Hipólito O’Farrill-Nieves, Silverio Medina-Gaud. University of Puerto Rico. 2007.
  • “Plants to cure plants. To treat orchard and garden problems without chemicals ”, Bernard Bertrand, Jean-Paul Collaert, Eric Petiot.
  • “Ecological techniques and treatments for urban gardens”, Dipotació de Valencia. 2014

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