Efficacy of Systiva® Seed Treatment in Managing Tan Spot and Septoria Leaf Blotch in Winter Wheat

This study evaluates the efficacy of fluxapyroxad as a seed treatment fungicide for the control of major foliar pathogens in wheat. The research aims to highlight its potential as a preventative and curative agent within integrated disease management strategies.

Fluxapyroxad-general

Fluxapyroxad is a pyrazole-4-carboxamide fungicide widely used for its broad-spectrum antifungal activity, high efficiency and low toxicity [1,2]. It is structurally related to boscalid and contains the difluoro methyl-substituted pyrazole acid building block and the biphenyl parts [3]. Fluxapyroxad acts as a Succinate Dehydrogenase Inhibitor (SDHI) [4-6] and has been found to have comparable efficacy to boscalid against various fungi [4]. Its mechanism of action involves inhibiting the SDH enzyme, disrupting the electron transport in the complex II-oxidation of succinic acid to fumarate in fungi, and disrupting cellular energy metabolism [7]. Furthermore, the fungicidal activities of fluxapyroxad, along with other Succinate Dehydrogenase Inhibitors (SDHIs), have been evaluated and it has been found to inhibit succinate dehydrogenase in complex II of the mitochondrial respiratory chain, leading to the inhibition of mycelial growth within the fungus target species [8].

Mode of action of fluxapyroxad against wheat pathogens

Fluxapyroxad functions as a Succinate Dehydrogenase Inhibitor (SDHI), targeting key wheat pathogens such as Pyrenophora tritici-repentis and Zymoseptoria tritici [9,10]. SDHIs interfere with various key fungal life functions, including spore germination, germ tube growth, appressoria formation and mycelium growth. Specifically, fluxapyroxad inhibits the activity of succinate dehydrogenase, an essential enzyme within complex II of the mitochondrial respiratory chain. This disruption impairs the Tricarboxylic Acid (TCA) cycle and electron transport processes, ultimately leading to a breakdown in cellular energy metabolism and suppression of pathogen growth and development [11]. It is important to note that resistance to fluxapyroxad has been observed in some fungal pathogens, such as Botrytis cinerea. However, there is no cross-resistance between fluxapyroxad and other fungicides with different modes of action [12,13]. Our findings demonstrate that fluxapyroxad, when applied as a seed treatment fungicide, effectively disrupts the development of major wheat pathogens, including P. tritici-repentis, the causal agent of tan spot disease [14].

Fluxapyroxad and Pyrenophora tritici-repentis

Pyrenophora tritici-repentis is a fungal pathogen that causes tan spot disease in wheat. Tan spot disease, also known as yellow spot, yellow leaf spot, yellow leaf blotch, or helminthosporiosis, is a significant fungal disease that affects wheat crops worldwide [15,16]. The fungus overwinters on stubble and can cause increased incidence and yield loss if ideal conditions occur [17]. The disease is one of the most important fungal diseases of wheat and is found in all regions of the world where wheat and other susceptible host crops are cultivated. Fluxapyroxad has been studied for its effectiveness in managing tan spot disease in wheat. Research indicates that when used in conjunction with integrated agronomic practices (such as nitrogen fertilization and silicon soil amendments), fluxapyroxad significantly reduces disease severity [17]. As mentioned above, the use of fluxapyroxad as a seed treatment fungicide offers a proactive approach to suppressing P. tritici-repentis, thereby mitigating yield losses and enhancing crop resilience.

Fluxapyroxad as a seed treatment fungicide

Although fluxapyroxad is primarily applied as a foliar spray, its potential as a seed treatment fungicide has garnered increasing attention. Seed-applied fungicides, including fluxapyroxad, have demonstrated significant benefits in reducing disease severity and enhancing overall plant health and productivity. Studies have shown that seed treatments can improve early plant vigor, increase winter survival rates and boost grain yield by 25-50% [18]. Systiva®, a fluxapyroxad-based fungicide formulated for seed treatment, has proven effective in protecting wheat crops against a range of pathogens. Notably, its application has been associated with reduced infection rates of P. tritici-repentis and Zymoseptoria tritici during critical early growth stages (GS23-25 and GS30- 31), contributing to improved crop establishment and disease suppression [14].

Objectives of this study

The primary objective of this study is to provide further evidence supporting the efficacy of Systiva® (a fluxapyroxad-based seed treatment fungicide) in reducing the incidence and severity of key foliar fungal diseases in wheat. Emphasis is placed on its effectiveness against P. tritici-repentis, the causal agent of tan spot disease, during the early growth stages of wheat development.

Field trials were conducted during the 2024-2025 growing season in the Larissa region of central Greece. Visual field measurements were employed to assess wheat tiller numbers and disease severity. The experiment was conducted in a 0.4-hectare field located in Larissa, central Greece, under minimum tillage conditions. A Randomized Complete Block Design (RCBD) was used, consisting of two treatments (Treated with Systiva® and Untreated -Control) and four replications. Each plot measured 10×4 meters, covering 160m² per treatment.

Methodology for tiller counting

Tiller density was assessed through direct visual field measurements following established agronomic protocols. In each experimental plot, tillers were counted along fixed-length rows-either three 1-meter rows or five 0.5-meter rows-depending on the season and plot layout. The total number of tillers within these measured segments was recorded and converted to tillers per square meter (tillers m^-2) using the known row spacing and sampling area. This method, as outlined by Scotford & Miller [19], provides a reliable estimate of tiller density, though it is laborintensive and subject to variability due to sampling position. To minimize bias, sampling locations were randomly selected within each plot and measurements were conducted at consistent growth stages to ensure comparability across treatments.

Disease assessment

Visual disease assessment of wheat foliar pathogens was conducted by evaluating symptomatic plant tissues affected by P. tritici-repentis and Septoria species. Observers evaluated 8-10 plants every meter between two crop rows, estimating the percentage of leaf area exhibiting blotching, chlorosis, or necrosis. Disease severity was quantified using a Standard Area Diagram (SAD), which provided reference images corresponding to 1%, 5%, 25%, 50% and 75% leaf area infection. This visual scoring method enabled consistent and reproducible evaluations across treatments. Assessments were carried out at 40 evenly spaced sampling points along each treatment path, with intervals of 0.35 meters between sites. All evaluations were performed during the wheat tillering stage, in accordance with the methodology described by Vagelas et al. [14].

Statistics

To evaluate the impact of Systiva® seed treatment on wheat tiller count and foliar disease severity, an independent samples t-test was conducted using JASP statistical software. The dataset consisted of two treatment groups (treated with Systiva® and Untreated- Control) with corresponding measurements for tiller density and disease severity scores. Each observation was considered independent and preliminary diagnostics were conducted to validate the assumptions of parametric testing. Normality of the data distribution was assessed using the Shapiro-Wilk test, while homogeneity of variances between groups was evaluated via Levene’s test. The t-test was applied to determine whether the mean differences in tiller count and disease severity between the two groups were statistically significant. To further interpret the practical relevance of the findings, effect sizes were calculated using Cohen’s d, accompanied by 95% confidence intervals to quantify the magnitude and precision of the observed effects.

The results of the independent samples t-test revealed a statistically significant difference in both tiller count (Figure 1) and disease severity (Figure 2) between wheat plants treated with Systiva® and those in the untreated control group. Systiva®-treated plants exhibited a notably higher mean tiller density (Figure 1), alongside substantially lower disease severity scores (Figure 2). Specifically, the reduction in mean disease severity among the treated group underscores the fungicidal efficacy of fluxapyroxad in suppressing early-season infections caused by P. tritici-repentis and Septoria spp. These results demonstrate that seed treatment with Systiva® not only enhances early plant vigor but also provides effective protection against foliar fungal pathogens under field conditions.

Figure 1:Number of wheat tillers in plants treated with Systiva® seed treatment fungicide compared to untreated controls.

Figure 2:Disease severity in wheat plants treated with Systiva® seed treatment fungicide compared to untreated control plants.

This study provides compelling evidence that seed treatment with Systiva® significantly improves early-stage wheat performance by increasing tiller density and reducing the severity of foliar fungal diseases compared to untreated controls. Statistical analysis using independent samples t-tests confirmed that these differences were both statistically significant and agronomically meaningful, with large effect sizes underscoring the robustness of the treatment’s efficacy. The results of this study reinforce the strategic value of fluxapyroxad-based seed treatments, such as Systiva®, within integrated disease management programs for wheat [14]. Specifically, Systiva® demonstrated effective suppression of earlyseason infections caused by P. tritici-repentis and Septoria spp., including Z. tritici, under natural field conditions. By enhancing plant vigor and suppressing pathogen pressure during critical developmental stages, Systiva® contributes to improved crop establishment and productivity under field conditions. Given the increasing disease risks associated with climate variability and residue-borne inoculum, further research is warranted to assess the long-term effectiveness of Systiva® across diverse agroecological zones and evolving pathogen populations. Such studies will help refine application strategies and ensure sustainable disease control in wheat production systems.

To expand upon the findings of this study, future research should explore the long-term efficacy of fluxapyroxad seed treatments across diverse agro-climatic zones and under varying pathogen pressures. Investigating the interaction between Systiva® and different wheat genotypes could reveal genotype-specific responses and optimize treatment recommendations. Additionally, integrating molecular diagnostics to monitor shifts in pathogen populations and resistance development would enhance early detection and inform adaptive management strategies. Comparative trials involving alternative fungicides and integrated disease control approaches (including crop rotation and resistant cultivars) could further validate the role of Systiva® within sustainable wheat production systems.