News » 22.09.2025 - Using Trichoderma the right way in root disease management
Trichoderma has long been a trusted ally for greenhouse growers aiming to manage root diseases and improve plant health. But not all Trichoderma strains, or microbial products, are created equal. Dr. Michael Brownbridge, Senior Technical Services Manager at BioWorks Inc., shares about the science behind their microbial formulations, how they're best used, and what growers can do to optimize their performance in integrated plant health programs.
Targeted strain selection: Not all Trichoderma are the same
"Different Trichoderma strains bring different tools to the table," Dr. Brownbridge says. "It's important not to generalize their capabilities. At BioWorks, we focus on strains that are highly competitive and well-studied."
RootShield WP and G products are based on Trichoderma harzianum strain T-22, while RootShield PLUS+ WP and G combine T-22 with Trichoderma virens strain G-41. According to Dr. Brownbridge, "Each strain brings multiple modes of action to bear against pathogens, including competitive exclusion, direct antagonism, and induction of plant defenses. In addition, T-22can effectively parasitize soil-borne pathogens."
Both strains offer benefits beyond pathogen suppression, including their capacity to enhance nutrient uptake, root growth, and overall plant vigor.
Pepper roots on Trichoderma selective. Roots were sampled from plants grown in a commercial hydroponic greenhouse. Plants had been treated earlier with RootShield PLUS WP. The fungal outgrowth onto the selective medium shows both T. harzianum T22 (tan brown in color) and T. virens G-41 (green), confirming colonization of the root by both strains.
Compatibility in the tank: What mixes, what doesn't
One common challenge for growers using biologicals is compatibility with synthetic inputs. "We run extensive compatibility trials each year," Dr. Brownbridge notes. "These include tests with fungicides, insecticides, PGRs, adjuvants, and sanitation products."
The results are compiled in an interactive online compatibility tool, regularly updated and accessible on the BioWorks website. "Many synthetic fungicides are compatible," he says, "but certain FRAC groups can negatively impact biocontrol organisms. That doesn't mean they can't be used together, just not at the same time."
He recommends applying incompatible materials separately, leaving a buffer of one to several days depending on the compound.
Shelf life and summer survival
Storage conditions play a big role in microbial viability. "We provide a detailed shelf-life guide that outlines expected product longevity under various temperature conditions. As a rule, avoid storing above 75°F (24°C) for extended periods."
Growers who want to confirm product viability can run microbiological assays, though this typically requires in-house lab capabilities. "For living biopesticides, a viability check is possible, but most of our customers rely on our label guarantees and best-by dates."
BioWorks' quality control, required under EPA registration, ensures consistent product viability and performance when used within recommended parameters.
Plant growth benefits of Trichoderma on Notocactus. A striking picture taken in a commercial greenhouse specializing in cacti and succulents – Trichoderma treated plants on the left (the propagation medium was treated with Trichoderma granular formulation), standard growing mix on the right
Application all about timing, not just rates
Growers often ask about reapplication intervals, especially for crops in inert media like rockwool. "There's no one-size-fits-all reapplication schedule," Dr. Brownbridge says. "It depends on the crop, substrate, environment, and disease pressure."
That said, he offers a guiding principle: "We advocate for lower rates with more frequent applications, rather than high rates with longer gaps." This helps maintain consistent microbial populations and root protection.
In rockwool-grown vegetables, for instance, shorter intervals are key due to the lack of organic matter to support microbial persistence. In contrast, coco or peat-based media can support longer intervals between treatments.
Better formulations, better results
"Stabilizing the spores, ensuring easy preparation, and preventing application issues are all critical," he emphasizes.
Recent upgrades to BioWorks' formulations reflect these priorities. For example, insoluble inerts were eliminated from the RootShield PLUS WP formulation, improving solubility and reducing the risk of clogging in drip and overhead systems. BotryStop has been reformulated from a WDG to a room-temperature-stable product with easier mixing and storage. PRINCIPLE-WP, a Beauveria bassiana product, was developed using two decades of formulation experience, offering a product with low residue, ease of use, and competitive efficacy.
While formulation details are proprietary, all components are EPA-approved and OMRI-listed for organic use.
What happens after application?
Understanding how introduced microbes affect the native soil microbiome is complex. While BioWorks hasn't conducted in-house microbiome studies, the company has supported and reviewed academic research.
"Trichoderma tends to promote beneficial microbes like Bacillus and Pseudomonas, while suppressing pathogens like Rhizoctonia and Fusarium," he says. "But these effects tend to be non-permanent and localized."
Plant species, age, and root exudates often play a larger role in shaping microbial communities than the biopesticide itself. "In greenhouses with inert media, Trichoderma often helps fill the microbial vacuum, which is one reason why we see improved plant health outcomes."
T22 parasitizing Rhizoctonia. This SEM image shows how T. harzianum T-22 strain parasitizes Rhizoctonia, here showing penetration of the pathogen by hyphae of T-22
Quality over quantity
The debate over single-strain versus multi-strain products is ongoing, but Dr. Brownbridge shares that more is not always better.
"Products with 10, 20, or more strains may sound impressive, but most microbes are highly competitive. In a limited resource environment like the root zone, only the strongest survive. Plus, we know that many product claims don't match the content of the package."
BioWorks favors well-researched, competitive strains in higher concentrations. "You want strains that establish quickly and deliver consistent results across crops and conditions. That's the value of T-22 and G-41."
Verifying establishment in the rhizosphere
Growers often want to know if the microbes they applied are actually colonizing roots. "We can verify colonization by plating root samples on selective media," he explains. "Trichoderma will grow out from the roots if it's there."
Quantitative assays can go further, measuring colonization levels. "We periodically offer this service to customers," he adds, "and it can be a great tool for troubleshooting or validation."
Be strategic, not just biological
Ultimately, microbial success comes down to strategic integration, not just product choice. "Biologicals are powerful tools, but they must be used thoughtfully," says Dr. Brownbridge. "That means understanding your crop, your system, and how microbial products fit into the bigger picture of plant health. We're here to be partners in plant health."
Source: www.floraldaily.com
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