A single-mode fungicide targets one specific biochemical process or pathogen site. For instance, QoI fungicides (also called strobilurins) inhibit mitochondrial respiration. These modes are efficient but vulnerable. Once a fungal population develops resistance to this one action site, the fungicide becomes ineffective.
Resistance develops when the same fungicide is used repeatedly across growing seasons without rotation or mixing with other mechanisms. This risk intensifies when weather, economic pressure, and crop susceptibility limit farmers’ flexibility.
Resistance to fungicides is an evolutionary adaptation. A few naturally resistant fungus cells may survive when the majority are killed by a fungicide. These resistant strains take over if the fungicide is administered without an alternative defence mechanism.
Key contributors include:
Repeated use of the same fungicide chemistry.
Inadequate dosages that fail to kill all pathogens.
Lack of diversity in disease management tools.
Research from FRAC (Fungicide Resistance Action Committee) confirms that narrow-spectrum fungicides are among the fastest to encounter resistance in high-pressure environments. Specific pathogens, such as Zymoseptoria tritici in wheat and Plasmopara viticola in grapevines, already exhibit resistance trends globally.
Yes. Over-reliance on a single fungicide class has cumulative risks. Even in regions with integrated pest management (IPM) strategies, economic and operational pressures sometimes override best practices.
Input cost constraints, leading to reduced fungicide diversity.
Marketing pressure from agrochemical firms focusing on specific products.
Yield urgency, which encourages fast-acting, single-mode fungicides.
According to a 2022 poll, 64% of farmers in the soybean-growing region of Brazil consistently used one or two active substances. Over four seasons, this resulted in a 37% reduction in fungicide efficacy.
Adrone Azoxystrobin 18.2% + Difenoconazole 11.4% SC Fungicide, which combines two distinct mechanisms of action, is essential to preserving fungicide efficacy. As a result, the pathogen's capacity for adaptation and survival is diminished. Dual-action fungicides, as opposed to single-mode treatments, distribute selective pressure to provide superior control and safeguard crop production.
Fungicide dependency varies by crop type. High-value crops that are sensitive to fungal disease see the highest reliance rates.
Crop Type | Common Fungicides Used | Resistance Observed |
Wheat | Azoles, Strobilurins | Z. tritici |
Grapevines | QoI, DMI | P. viticola |
Soybean | QoI, SDHI | C. cassiicola |
Bananas | Benzimidazoles, DMIs | Black Sigatoka |
In many banana plantations, Black Sigatoka has shown resistance to multiple fungicides due to continuous use without mode rotation. This has led to increased costs and heightened crop vulnerability, particularly in monoculture systems.
Crop rotation helps mitigate the burden of disease, but when fungicides are not altered, the resistance problem persists. The selective pressure endures if the same fungicide is applied to various crops.
For instance, if a product is labelled as "broad-spectrum," a farmer who grows both maize and soybeans may nevertheless use QoI fungicides on both crops. The fungus only adjusts to the chemistry and doesn't care what kind of crop it is.
Avoid using the same fungicide across multiple crops.
Implement multi-site fungicide use where available.
Integrated practices must include rotation, resistant varieties, biological controls, and chemical diversity.
"The power of a fungicide lies not in its chemistry alone, but in the strategy behind its use."
– Dr. Elena Torres, Plant Pathologist, Wageningen University
When fungicides lose efficacy, farmers face multiple economic challenges:
Increased input costs: Farmers must apply higher dosages or more expensive combinations.
Reduced yield protection: Crop losses rise when diseases break through chemical barriers.
Shrinking chemical options: Regulatory bans on specific actives limit future alternatives.
In the UK, resistance to DMI fungicides in wheat pathogens has led to a 15% increase in disease management costs since 2019, according to data from AHDB.
Building a multi-faceted disease control strategy reduces dependency. Here’s how farmers can act:
Use FRAC codes to select fungicides with different action modes.
Avoid repeating the same FRAC group in consecutive applications.
Use resistant cultivars.
Maintain proper spacing and airflow.
Monitor for disease thresholds before applying fungicides.
Some biofungicides, like Bacillus subtilis, are effective as preventatives. While not always standalone solutions, they reduce chemical burden.
Biological fungicide resource – Bioprotection Portal
Stay informed with resistance monitoring networks and extension services.
Global FRAC resources provide resistance maps and management advice tailored to each region and crop.
Yes, although they often require more planning and labor. Alternatives include:
Cover cropping: Suppresses pathogen cycles.
Soil amendments: Improve microbial health, limiting disease expression.
Precision agriculture tools: Allow targeted applications based on disease models.
An example includes the use of spatiotemporal disease prediction models in rice paddies in Southeast Asia, which has reduced unnecessary fungicide spraying by 21%.
Manufacturers of agrochemicals are spending money on formulations with two or more modes. These aid in delaying the development of resistance. Newer SDHI + DMI combinations, for instance, provide more control and lessen resistance pressure.
In an effort to encourage stewardship, companies are now introducing label revisions that incorporate usage limitations and resistance warnings.
Manufacturers are also subject to regulatory pressure. For instance, because of safety and resistance issues, the EU has been gradually eliminating more than 30 active ingredients since 2018.
The window to preserve fungicide efficacy is narrowing. Delayed action will accelerate resistance, reduce yield stability, and drive chemical innovation costs higher. Sustainable stewardship involves collaboration across the entire supply chain—from manufacturers to farmers.
Key practices include:
Reading and following label instructions.
Rotating actives, not just brand names.
Applying only when thresholds are reached.
Global examples demonstrate that poor stewardship results in shorter product lifespans. In Argentina, resistance to strobilurins in soybean rust developed within five years of the initial introduction, largely due to mono-use patterns.
FAQs
What is the difference between single-mode and multi-mode fungicides?
Single-mode fungicides attack one target site; multi-mode ones attack multiple. Multi-mode reduces the risk of resistance buildup.
How do I know which FRAC group my fungicide belongs to?
FRAC codes are listed on fungicide labels. You can also check the FRAC Code List for reference.
Can I rotate fungicides within the same brand?
No. Brands may contain the same active ingredient. Rotate by FRAC code, not brand.
How often should I rotate fungicides?
At least every application cycle, and definitely between seasons. Avoid using the same FRAC code more than twice per season.
Are biological fungicides effective?
They are effective as part of an integrated system, especially for prevention. They may not perform as curatives under heavy disease pressure.