Struggling with root diseases like Pythium or Fusarium? In many greenhouses, these outbreaks are still seen as sudden events. Something that enters the system and needs to be removed as quickly as possible. In reality, these pathogens are often already present. The real question is not whether they are there, but why they are able to develop into a problem.
Interview with microbial ecologist Marta Streminska (Wageningen University & Research)
Cultivating resilience in the rootzone
Published: May 1, 2026
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What microbiology teaches us about plant health in modern greenhouses
In a recent interview, microbial ecologist Marta Streminska (Wageningen University & Research) explains that the answer lies in how we manage the rootzone. Within the Plant Health Circle, a disease only becomes a real problem when three elements come together: the pathogen is present, the conditions are favourable, and the plant is susceptible. The rootzone is where these elements meet, making it one of the most important areas to understand and manage.
A healthy rootzone is not sterile
For a long time, the ideal rootzone was often described as clean or even sterile. However, microbiology tells a different story. A healthy rootzone is not empty, but active. It supports plant development while maintaining enough resilience to handle the presence of pathogens.
In such a system, organisms like Pythium or Fusarium may be present, but they are unable to establish themselves or cause damage. This shift in thinking is becoming increasingly important as pathogens develop resistance to chemical treatments and continue to persist in soilless systems through long-living survival structures.
Microbiology and recirculating water systems
This perspective also changes how we look at water management. With the transition towards recirculating water systems, many growers are concerned about the accumulation of microorganisms in reused drain water.
Research shows that microbial life is always present, often in high concentrations. Yet this does not automatically lead to problems. Most systems remain stable as long as they are not disturbed. Large fluctuations in microbial activity are usually the result of management decisions, such as excessive use of organic inputs or sudden changes in the system.
When these imbalances occur, they can lead to uncontrolled microbial growth or practical issues like clogging. Under stable conditions, however, microbial populations tend to remain in balance.
The plant shapes its own microbiome
One of the most important insights is that the plant itself plays a central role in shaping the microbial environment in the rootzone. Through root exudates, plants release organic compounds that influence which microorganisms develop around the roots.
While the type of substrate can affect which species are present, the plant remains the dominant driver. Whether grown in stonewool or coco peat, the microbial community may differ in composition, but often performs similar functions that support plant growth and resilience. This means that managing plant health is directly linked to understanding how the plant interacts with its microbial environment.
From control to balance
The growing availability of biostimulants and water treatments offers new opportunities, but also requires a more strategic approach. Products that influence microbiology can be valuable, but their effectiveness depends strongly on how and why they are used.
Applying them without a clear goal can disturb the balance rather than improve it. The same applies to disinfectants. While they help reduce pathogen pressure, they are not selective and can also affect beneficial microorganisms and even root health if overused.
The goal is therefore not to create a sterile system, but to maintain a balanced one, where pathogens are controlled without disrupting the underlying biology.
Stability as the foundation of plant health
In practice, this means that rootzone management is less about reacting to visible problems and more about creating stable conditions from the start. Stability in water, oxygen, nutrition and microbiology allows the plant to function optimally and reduces the likelihood that pathogens can take over.
When these conditions fluctuate, the system becomes more vulnerable, and small disturbances can quickly develop into larger issues. Understanding microbiology adds another layer to how we look at plant health. It shows that root diseases are rarely isolated incidents, but the result of interactions within the system.
Is plant health about eliminating risks or managing the system?
By focusing on resilience instead of elimination, growers can move towards a more stable and self-supporting growing strategy. In that sense, plant health is not about removing risk, but about managing the system in such a way that risks do not develop into problems.
This article is part of the Plant Health Year Program, where we explore different methods for measuring and understanding plant health.
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