Microbes not only provide the plant with nutrients, but also protect it from disease and pests. The complete network of microorganisms covers all parts of the plant with a strong layer and acts as a shield against parasites.
The key to understanding the role of the food web in protecting plants against parasites is the biodiversity of the plant's ecosystem. The plant becomes a small universe in which everyone has a role to play.
One of the mechanisms plants use to create immunity is to harness other organisms to work. In the course of evolution, plants have developed a whole host of such strategies. Examples can be multiplied: insect pollination, seed dispersal by animals, insectivorousness, symbiosis with specific species of insects, mycorrhiza and many others. In most of these examples, the plant secretes some food that becomes the currency in settlements with its ally. In the case of the immune system, we see a similar pattern. Exudates secreted by the plant they attract and feed a whole lot of microorganisms, the species composition of which is regulated by the composition of compounds secreted by the plant. They are designed to compete with pathogens and prevent their growth and even actively attack. This applies to pathogenic bacteria, fungi and more complex life forms. Let's trust this process.
We must also remember that it is not the solution to kill a given species of "pest" on our crops. Only a healthy ecosystem provides stable conditions and keeps all species in balance with each other. Getting rid of a given "pest" completely may also cause the disappearance of the corresponding parasites and predators. Which, in turn, will lead to an imbalance and create conditions for a population outbreak of exactly the species we were fighting. Let us support plants in their natural struggle with their enemies. We can do this by spraying compost tea, which will enrich the biodiversity of aerobic microorganisms. Thanks to this, the plants will regulate themselves which of them will suit them best from the point of view of pest control.
It should also be added that plant diseases and parasite invasions are, just like in humans, a symptom and not a cause of disturbed homeostasis. Here, equilibrium lies in the complex relationships between organisms. Just as in humans, the sterilization of the digestive system or skin causes a general upset or an attack of mycosis, in plants, disturbances in the layer of microorganisms covering the plant allow pathogens to attack. The situation is similar for insects, which are unable to digest the very complex sugars that build healthy plant cell walls.