Findings from this research indicate that the presence of oxidising agents, which are primarily applied for the control of biofilm within irrigation lines, may act both as a trigger and as a modifier of symptom expression. Based on these insights, Grodan has issued new hygiene-related advice to help growers avoid unintentionally making their crops more susceptible. Growers welcome the greater insight into an important factor contributing to pepper wilting.
Evidence-based insights
Since 2022, high-tech pepper growers have faced uncertainty and confusion due to sporadic outbreaks of pepper wilting. As a supplier committed to supporting growers by providing evidence-based insights to guide their decision-making, Grodan was keen to help the industry find a solution. The company therefore proactively embarked on an extensive international research programme.
Besides participating in several externally led consortia trials, Grodan funded its own independent research studies in collaboration with respected institutions in the Netherlands, Belgium and Canada. As part of its investigations, Grodan also closely analysed the operational practices of over a dozen growers, and conducted tests on sample slabs and plant materials obtained from growers who had experienced pepper-wilting symptom expression.
“In the group analysed, growers experiencing wilting had measurable oxidising agent concentrations at the dripper,” says Frank Janssen, Grodan’s R&D Manager. “This strengthened our hypothesis that oxidising agents entering the root zone both initiate and increase symptom expression in pepper wilting.“
Differences in chemical persistence
The Grodan team investigated what might be modifying symptom expression by comparing the effects of dosing an oxidising agent (in this case, hydrogen peroxide) in both stone wool and organic substrates. The findings suggest that substrate composition influences the chemical persistence of oxidising agents, which in turn affects the extent of root tissue exposure and potential root damage. This explains observed differences in symptom expression between substrate types under certain conditions, according to Janssen.
“However, this does not mean that organic substrates are safer for peroxide treatment. Importantly, faster degradation in organic substrates does not eliminate the potential for root stress,” adds Andrew Lee, Head of Crop Advice, Europe and Asia at Grodan.
Non-linear interaction in presence of Fusarium
Subsequently, the company tested its hypothesis by applying various concentrations of hydrogen peroxide to plants inoculated with Fusarium oxysporum f. sp. radicis-capsici (FORC). Independent studies had previously identified this pathogen as one of the likely causes of pepper wilting.
The results revealed a non‑linear interaction between dose concentration and symptom expression, with the plants receiving 50 ppm of hydrogen peroxide being the first to exhibit wilting symptoms. This provided a pivotal insight and enabled the team to further refine and test the hypothesis.
Rethinking common hygiene practices
The findings suggest that certain hygiene practices, although well-intended, may contribute to increased plant vulnerability under specific conditions in the root zone. “Although hydrogen peroxide can be an appropriate sanitation tool because it breaks down into water and oxygen after completing its disinfecting action, this does not mean that dosing oxidising agents into the active root zone is safe or beneficial. The same chemical reactivity that helps clean irrigation lines becomes harmful when it comes into direct contact with living roots,” explains Lee.
Furthermore, continued use of oxidising agents may significantly disrupt the root‑zone microbiome – a system that is essential for overall plant resilience – and may reduce the efficacy of plant protection products, according to Lee.
New recommendations for growers
Based on these insights, Grodan has fine-tuned its advice for growers who want to use oxidising agents as part of their hygiene practices to control biofilm build-up in irrigation systems. “Besides following legal regulations and the supplier’s instructions, we recommend avoiding measurable concentrations of any oxidising agent in the root zone during cultivation,” he emphasises.
“Growers have expressed appreciation for the greater clarity on an important factor contributing to pepper wilting. We are continuing to monitor the reactions from the market and, where necessary, we will further fine-tune our guidance to reduce the risk of pepper wilting and to support resilient crop development under high-tech growing conditions,” Lee concludes.
More details of the extensive research programme and results can be found here.
