---
title: "Fungicide FRAC Code Calculator: Stop Resistance Before It Destroys Your Chemical Program"
canonical: "https://theyieldgrid.com/fungicide-frac-code-calculator/"
model_id: "tyg-880"
model_version: "1.0.0"
last_reviewed: "2026-08-24T08:35:31"
reviewed_by: "Umer Hayiat"
---

# Fungicide FRAC Code Calculator: Stop Resistance Before It Destroys Your Chemical Program

> Canonical calculator: [https://theyieldgrid.com/fungicide-frac-code-calculator/](https://theyieldgrid.com/fungicide-frac-code-calculator/)

## What this calculator does

Home - Free Gardening Calculators & Tools - Fungicide FRAC Code Calculator: Stop Resistance Before It Destroys Your Chemical Program Turf disease failures do not always come from applying the wrong fungicide. They come from applying the right fungicide too many times in a row. Every single-site inhibitor works by targeting one specific enzyme in the fungal cell. That precision is the source of its power, and the exact mechanism that allows pathogen populations to evolve complete resistance through a single point mutation. The spray that worked perfectly in June can become useless by August, not because the product changed, but because the surviving mutants were the only ones left to reproduce.

## Inputs

| Input | ID | Type | Unit | Range or choices | Required |
|---|---|---|---|---|---|
| Target Disease | `fracrot_disease` | select |  | — Select Disease — = ``; Brown Patch (Rhizoctonia solani) = `brown_patch`; Dollar Spot (Sclerotinia homoeocarpa) = `dollar_spot`; Pythium Blight = `pythium_blight`; Anthracnose = `anthracnose`; Gray Leaf Spot = `gray_leaf_spot`; Summer Patch = `summer_patch`; Snow Mold (Pink/Gray) = `snow_mold`; Take-All Root Rot = `take_all` | Yes |
| Last Applied Active Ingredient | `fracrot_last_ai` | select |  | — Select Active Ingredient — = ``; Azoxystrobin (Heritage) = `azoxystrobin_11`; Pyraclostrobin = `pyraclostrobin_11`; Trifloxystrobin = `trifloxystrobin_11`; Fluoxastrobin = `fluoxastrobin_11`; Propiconazole (Banner Maxx) = `propiconazole_3`; Myclobutanil = `myclobutanil_3`; Tebuconazole = `tebuconazole_3`; Triadimefon = `triadimefon_3`; Metconazole = `metconazole_3`; Boscalid = `boscalid_7`; Fluopyram = `fluopyram_7`; Fluxapyroxad = `fluxapyroxad_7`; Penthiopyrad = `penthiopyrad_7`; Metalaxyl / Mefenoxam = `metalaxyl_4`; Thiophanate-methyl (Cleary 3336) = `thiophanate_1`; Chlorothalonil (Daconil) = `chlorothalonil_M5`; Mancozeb = `mancozeb_M3`; Iprodione (FRAC 2 / Dicarboximide) = `iprodione_2` | Yes |
| Days Since Last Application | `fracrot_interval` | number | Days | 1 to 365 | Yes |

## Outputs

| Output ID | Default state |
|---|---|
| `fracrot_results` | Resistance Risk Level — Low Risk Critical — Do Not Reapply Safe to Reapply Rotation Advised RESISTANCE WARNING FRAC Code Reference — Resistance Risk by Mode of Action FRAC Code Mode of Action Example A.I. Resistance Risk Site Specificity FRAC 11 QoI — Strobilurins Azoxystrobin, Pyraclostrobin HIGH Single-site FRAC 7 SDHI — Succinate Dehydrogenase Boscalid, Fluopyram HIGH Single-site FRAC 3 DMI — Triazoles/Sterol Biosyn. Propiconazole, Tebuconazole MEDIUM Single-site FRAC 1 MBC — Benzimidazoles T |
| `fracrot_status_dot` |  |
| `fracrot_out_primary` | — |

## Formula and method

Show the calculation steps Step 1: Active Ingredient to FRAC Code Lookup The calculator maintains a deterministic lookup table of active ingredients mapped to their FRAC code, mode of action group, site specificity class (single-site vs. multi-site), and baseline resistance risk class (HIGH / MEDIUM / LOW). When you select an active ingredient, the FRAC code and associated risk parameters are retrieved from this table. No interpolation occurs; the lookup is categorical. Step 2: Risk Class Assignment Risk class is assigned at the FRAC code level, not the product level: FRAC 11, 7, 1, 4: HIGH (single-site; one mutation sufficient to confer resistance) FRAC 3, 2: MEDIUM (single-site but polygenic resistance mechanisms; gradual population shift) FRAC M3, M5: LOW (multi-site; simultaneous mutations required across many targets) Step 3: Interval Threshold Logic Our algorithm monitors the critical 21-day window where repeated applications create maximum selection pressure for resistant "super-fungus" strains. The spray interval is compared against a 21-day resistance pressure threshold for HIGH-risk FRAC codes: HIGH risk + interval 14 days or less: Critical resistance alert, gauge score 95/100 HIGH risk + interval 15 to 21 days: Critical resistance alert, gauge score 80/100 HIGH risk + interval greater than 21 days: Moderate risk, gauge score 55/100, rotation still advised MEDIUM risk + interval 21 days or less: Moderate risk, gauge score 50/100 LOW risk at any interval, or MEDIUM risk beyond 21 days: Low risk, gauge score 20/100 Step 4: Rotation Recommendation Lookup The rotation map assigns pre-validated alternative FRAC codes for each FRAC group. For example, FRAC 11 maps to FRAC 3, FRAC 7, FRAC M5, and FRAC M3 as rotation partners. The first two alternatives listed are single-site options for curative efficacy; the last two are multi-site options for resistance reset. The recommendation always leads with a curative option first. Rounding and Display Rules Gauge percentage is an integer. Rate guidance is shown as a range without rounding, sourced from standard label ranges. Interval input accepts whole days only; the calculator does not process decimal values. Assumptions and Limits Resistance risk is modeled at the population level. Individual plants may show disease symptoms even with a "Low Risk" result if pathogen pressure is extreme or if application coverage was incomplete. The 21-day threshold is a broadly accepted practical guideline, not an absolute regulatory standard. Some disease programs and specific pathogen populations may require shorter rotation windows. The tool does not account for tank-mix chemistry. If your last application included two active ingredients from different FRAC codes, enter the higher-risk FRAC code as the primary input. Application rate guidance represents typical turf label ranges per 1,000 square feet. Rates for other use areas, ornamentals, or high-pressure disease situations require independent label verification. The calculator uses 2024 FRAC code assignments. Products registered after this date or reformulations with new active ingredients may not appear in the active ingredient dropdown. Weather, canopy moisture, and nitrogen fertility all affect actual disease pressure and fungicide efficacy. This tool models chemistry risk only, not agronomic field conditions. Resistance status of local pathogen populations is not factored in. In regions with confirmed FRAC 11-resistant Brown Patch or FRAC 3-resistant Dollar Spot populations, the critical threshold should apply to any repeat application of that FRAC code regardless of interval.

## Verified worked examples

### Example 1: Golf Course Green With Repeated Strobilurin Applications

Target Disease: Brown Patch Last Applied Active Ingredient: Azoxystrobin (Heritage) [FRAC 11, HIGH risk, Single-site] Days Since Last Application: 10 Result: CRITICAL: Resistance Alert. Gauge at 95/100. Traffic light: Resistance Warning. Super-Fungus alert triggered. FRAC 11 is a single-site QoI inhibitor applied within 10 days of the previous FRAC 11 application. The tool identifies this as maximum selection pressure: susceptible individuals in the pathogen population were killed by the first application, and the surviving population now skews heavily toward the resistant minority. A third FRAC 11 application will not control Brown Patch. The required action is an immediate switch to FRAC 3 (DMI triazole) or FRAC M5 (Chlorothalonil) before the next spray cycle.

### Example 2: Fairway Dollar Spot Program Using Triazoles

Target Disease: Dollar Spot Last Applied Active Ingredient: Propiconazole (Banner Maxx) [FRAC 3, MEDIUM risk, Single-site] Days Since Last Application: 21 Result: Moderate: Rotation Advised. Gauge at 50/100. Traffic light: Rotation Advised. FRAC 3 carries documented resistance history in Dollar Spot populations, particularly in turf with multi-year DMI-heavy programs. At exactly 21 days, the interval sits at the boundary of the resistance pressure window. The tool recommends rotating to FRAC 11 (Azoxystrobin), FRAC 7 (Boscalid), or FRAC M5 (Chlorothalonil) for the next application. Staying with FRAC 3 at this interval is not catastrophic but represents unnecessary compounding of resistance risk given that alternatives are available.

### Example 3: Home Turf Pythium Protection With Multi-Site Chemistry

Target Disease: Pythium Blight Last Applied Active Ingredient: Chlorothalonil (Daconil) [FRAC M5, LOW risk, Multi-site] Days Since Last Application: 14 Result: Low Risk: Rotation Optional. Gauge at 20/100. Traffic light: Safe. Multi-site inhibitors require simultaneous mutations at numerous biochemical targets to confer resistance. No confirmed resistance to Chlorothalonil has been documented in turfgrass oomycetes or fungi under field conditions. At 14 days, a repeat FRAC M5 application is acceptable from a resistance standpoint. The tool suggests rotating to a single-site FRAC code (FRAC 11 or FRAC 3) on the next application for improved efficacy against active infection, reserving FRAC M5 for the protective slots in the rotation program.

## Assumptions

This tool provides advisory guidance only — always read and follow product labels. Resistance status of local pathogen populations may vary by geography and history of use. Weather, temperature, and disease pressure may override rotation timing guidance. Some disease/fungicide combinations are off-label — consult an agronomist or licensed applicator. FRAC codes shown reflect FRAC 2024 publication; verify current listing for new products. Multi-site fungicides (FRAC M) are generally tank-mixed — standalone efficacy may be lower on some diseases. Show the calculation steps Step 1: Active Ingredient to FRAC Code Lookup The calculator maintains a deterministic lookup table of active ingredients mapped to their FRAC code, mode of action group, site specificity class (single-site vs. multi-site), and baseline resistance risk class (HIGH / MEDIUM / LOW). When you select an active ingredient, the FRAC code and associated risk parameters are retrieved from this table. No interpolation occurs; the lookup is categorical. Step 2: Risk Class Assignment Risk class is assigned at the FRAC code level, not the product level: FRAC 11, 7, 1, 4: HIGH (single-site; one mutation sufficient to confer resistance) FRAC 3, 2: MEDIUM (single-site but polygenic resistance mechanisms; gradual population shift) FRAC M3, M5: LOW (multi-site; simultaneous mutations required across many targets) Step 3: Interval Threshold Logic Our algorithm monitors the critical 21-day window where repeated applications create maximum selection pressure for resistant "super-fungus" strains. The spray interval is compared against a 21-day resistance pressure threshold for HIGH-risk FRAC codes: HIGH risk + interval 14 days or less: Critical resistance alert, gauge score 95/100 HIGH risk + interval 15 to 21 days: Critical resistance alert, gauge score 80/100 HIGH risk + interval greater than 21 days: Moderate risk, gauge score 55/100, rotation still advised MEDIUM risk + interval 21 days or less: Moderate risk, gauge score 50/100 LOW risk at any interval, or MEDIUM risk beyond 21 days: Low risk, gauge score 20/100 Step 4: Rotation Recommendation Lookup The rotation map assigns pre-validated alternative FRAC codes for each FRAC group. For example, FRAC 11 maps to FRAC 3, FRAC 7, FRAC M5, and FRAC M3 as rotation partners. The first two alternatives listed are single-site options for curative efficacy; the last two are multi-site options for resistance reset. The recommendation always leads with a curative option first. Rounding and Display Rules Gauge percentage is an integer. Rate guidance is shown as a range without rounding, sourced from standard label ranges. Interval input accepts whole days only; the calculator does not process decimal values. Assumptions and Limits Resistance risk is modeled at the population level. Individual plants may show disease symptoms even with a "Low Risk" result if pathogen pressure is extreme or if application coverage was incomplete. The 21-day threshold is a broadly accepted practical guideline, not an absolute regulatory standard. Some disease programs and specific pathogen populations may require shorter rotation windows. The tool does not account for tank-mix chemistry. If your last application included two active ingredients from different FRAC codes, enter the higher-risk FRAC code as the primary input. Application rate guidance represents typical turf label ranges per 1,000 square feet. Rates for other use areas, ornamentals, or high-pressure disease situations require independent label verification. The calculator uses 2024 FRAC code assignments. Products registered after this date or reformulations with new active ingredients may not appear in the active ingredient dropdown. Weather, canopy moisture, and nitrogen fertility all affect actual disease pressure and fungicide efficacy. This tool models chemistry risk only, not agronomic field conditions. Resistance status of local pathogen populations is not factored in. In regions with confirmed FRAC 11-resistant Brown Patch or FRAC 3-resistant Dollar Spot populations, the critical threshold should apply to any repeat application of that FRAC code regardless of interval. Resistance risk is modeled at the population level. Individual plants may show disease symptoms even with a "Low Risk" result if pathogen pressure is extreme or if application coverage was incomplete. The 21-day threshold is a broadly accepted practical guideline, not an absolute regulatory standard. Some disease programs and specific pathogen populations may require shorter rotation windows. The tool does not account for tank-mix chemistry. If your last application included two active ingredients from different FRAC codes, enter the higher-risk FRAC code as the primary input. Application rate guidance represents typical turf label ranges per 1,000 square feet. Rates for other use areas, ornamentals, or high-pressure disease situations require independent label verification. The calculator uses 2024 FRAC code assignments. Products registered after this date or reformulations with new active ingredients may not appear in the active ingredient dropdown. Weather, canopy moisture, and nitrogen fertility all affect actual disease pressure and fungicide efficacy. This tool models chemistry risk only, not agronomic field conditions. Resistance status of local pathogen populations is not factored in. In regions with confirmed FRAC 11-resistant Brown Patch or FRAC 3-resistant Dollar Spot populations, the critical threshold should apply to any repeat application of that FRAC code regardless of interval. Critical Warnings The two-application trap: Applying the same single-site FRAC code twice within one season appears safe and effective through the first cycle. The disease is suppressed, results look good, and the same product is purchased again. By the third application, the surviving pathogen population has been selectively enriched with resistant genotypes. The disease outbreak after the third application is not a product failure. It is a manufactured resistance event that began with the second application. Brand rotation is not FRAC rotation: Switching from Heritage to Compass, or from Banner Maxx to Eagle 20EW, appears to be a program change. Both Heritage and Compass are FRAC 11. Both Banner Maxx and Eagle 20EW are FRAC 3. The pathogen population does not register brand identity; it registers the mode of action. Switching brands within the same FRAC code provides no resistance management benefit. FRAC 3 resistance in Dollar Spot is not theoretical: Multi-year DMI-heavy programs on golf courses in the United States have produced populations with documented reduced DMI sensitivity. FRAC 3 moderate risk classification means resistance develops more slowly, not that it cannot develop. Combination products consume two FRAC codes simultaneously: Products like Lexicon (FRAC 11 + FRAC 7) are highly effective but use up two FRAC codes in a single spray. After using a combination product, both constituent FRAC codes must be rotated away from. Using a straight FRAC 11 product after a FRAC 11 + FRAC 7 pre-mix does not constitute rotation for FRAC 11. Minimum Standards Never apply the same single-site FRAC code more than two consecutive applications without inserting at least one multi-site FRAC M application. Programs targeting Dollar Spot should include FRAC M5 (Chlorothalonil) or FRAC M3 (Mancozeb) in every third application slot, regardless of current resistance status, as a structural program deposit against future selection pressure. Any program showing confirmed disease breakthrough on a product with a previously clean efficacy history should be treated as a resistance event, not an application error, until proven otherwise. Rotate to a different FRAC group immediately and document the incident. Competitor Trap: Most fungicide resistance guides list FRAC codes in a table and advise "rotating modes of action." They stop there. What those guides omit is the specific mechanism by which rotation timing matters as much as rotation itself. A grower who switches FRAC codes every 60 days but repeatedly uses a high-risk single-site code for back-to-back applications within each rotation block is still building resistance. The rotation chart looks correct on paper while the pathogen population continues to shift. This calculator measures the interval-specific pressure, not just whether a theoretical rotation plan exists on paper. Following a structured rotation schedule mirrors the logic behind organized crop sequencing: the succession planting chart illustrates how temporal diversity prevents biological monoculture vulnerabilities, a principle equally applicable to fungicide programs. Never apply the same single-site FRAC code more than two consecutive applications without inserting at least one multi-site FRAC M application. Programs targeting Dollar Spot should include FRAC M5 (Chlorothalonil) or FRAC M3 (Mancozeb) in every third application slot, regardless of current resistance status, as a structural program deposit against future selection pressure. Any program showing confirmed disease breakthrough on a product with a previously clean efficacy history should be treated as a resistance event, not an application error, until proven otherwise. Rotate to a different FRAC group immediately and document the incident. Competitor Trap: Most fungicide resistance guides list FRAC codes in a table and advise "rotating modes of action." They stop there. What those guides omit is the specific mechanism by which rotation timing matters as much as rotation itself. A grower who switches FRAC codes every 60 days but repeatedly uses a high-risk single-site code for back-to-back applications within each rotation block is still building resistance. The rotation chart looks correct on paper while the pathogen population continues to shift. This calculator measures the interval-specific pressure, not just whether a theoretical rotation plan exists on paper. Following a structured rotation schedule mirrors the logic behind organized crop sequencing: the succession planting chart illustrates how temporal diversity prevents biological monoculture vulnerabilities, a principle equally applicable to fungicide programs.

## Limitations and safety

This tool provides advisory guidance only — always read and follow product labels. Resistance status of local pathogen populations may vary by geography and history of use. Weather, temperature, and disease pressure may override rotation timing guidance. Some disease/fungicide combinations are off-label — consult an agronomist or licensed applicator. FRAC codes shown reflect FRAC 2024 publication; verify current listing for new products. Multi-site fungicides (FRAC M) are generally tank-mixed — standalone efficacy may be lower on some diseases. Resistance risk is modeled at the population level. Individual plants may show disease symptoms even with a "Low Risk" result if pathogen pressure is extreme or if application coverage was incomplete. The 21-day threshold is a broadly accepted practical guideline, not an absolute regulatory standard. Some disease programs and specific pathogen populations may require shorter rotation windows. The tool does not account for tank-mix chemistry. If your last application included two active ingredients from different FRAC codes, enter the higher-risk FRAC code as the primary input. Application rate guidance represents typical turf label ranges per 1,000 square feet. Rates for other use areas, ornamentals, or high-pressure disease situations require independent label verification. The calculator uses 2024 FRAC code assignments. Products registered after this date or reformulations with new active ingredients may not appear in the active ingredient dropdown. Weather, canopy moisture, and nitrogen fertility all affect actual disease pressure and fungicide efficacy. This tool models chemistry risk only, not agronomic field conditions. Resistance status of local pathogen populations is not factored in. In regions with confirmed FRAC 11-resistant Brown Patch or FRAC 3-resistant Dollar Spot populations, the critical threshold should apply to any repeat application of that FRAC code regardless of interval. Critical Warnings The two-application trap: Applying the same single-site FRAC code twice within one season appears safe and effective through the first cycle. The disease is suppressed, results look good, and the same product is purchased again. By the third application, the surviving pathogen population has been selectively enriched with resistant genotypes. The disease outbreak after the third application is not a product failure. It is a manufactured resistance event that began with the second application. Brand rotation is not FRAC rotation: Switching from Heritage to Compass, or from Banner Maxx to Eagle 20EW, appears to be a program change. Both Heritage and Compass are FRAC 11. Both Banner Maxx and Eagle 20EW are FRAC 3. The pathogen population does not register brand identity; it registers the mode of action. Switching brands within the same FRAC code provides no resistance management benefit. FRAC 3 resistance in Dollar Spot is not theoretical: Multi-year DMI-heavy programs on golf courses in the United States have produced populations with documented reduced DMI sensitivity. FRAC 3 moderate risk classification means resistance develops more slowly, not that it cannot develop. Combination products consume two FRAC codes simultaneously: Products like Lexicon (FRAC 11 + FRAC 7) are highly effective but use up two FRAC codes in a single spray. After using a combination product, both constituent FRAC codes must be rotated away from. Using a straight FRAC 11 product after a FRAC 11 + FRAC 7 pre-mix does not constitute rotation for FRAC 11. Minimum Standards Never apply the same single-site FRAC code more than two consecutive applications without inserting at least one multi-site FRAC M application. Programs targeting Dollar Spot should include FRAC M5 (Chlorothalonil) or FRAC M3 (Mancozeb) in every third application slot, regardless of current resistance status, as a structural program deposit against future selection pressure. Any program showing confirmed disease breakthrough on a product with a previously clean efficacy history should be treated as a resistance event, not an application error, until proven otherwise. Rotate to a different FRAC group immediately and document the incident. Competitor Trap: Most fungicide resistance guides list FRAC codes in a table and advise "rotating modes of action." They stop there. What those guides omit is the specific mechanism by which rotation timing matters as much as rotation itself. A grower who switches FRAC codes every 60 days but repeatedly uses a high-risk single-site code for back-to-back applications within each rotation block is still building resistance. The rotation chart looks correct on paper while the pathogen population continues to shift. This calculator measures the interval-specific pressure, not just whether a theoretical rotation plan exists on paper. Following a structured rotation schedule mirrors the logic behind organized crop sequencing: the succession planting chart illustrates how temporal diversity prevents biological monoculture vulnerabilities, a principle equally applicable to fungicide programs.

## Related calculators

- [Calculators & Tools](https://theyieldgrid.com/category/garden-calculators/)
- [neem oil mixing ratio calculator](https://theyieldgrid.com/neem-oil-mixing-ratio/)
- [growing degree days calculator](https://theyieldgrid.com/growing-degree-days-calculator/)
- [harvest date calculator](https://theyieldgrid.com/harvest-date-calculator/)
- [plant spacing calculator](https://theyieldgrid.com/plant-spacing-calculator/)
- [vegetable yield calculator](https://theyieldgrid.com/vegetable-yield-calculator/)
- [Prev Previous](https://theyieldgrid.com/grow-tent-fan-size-calculator/)
- [Next Next](https://theyieldgrid.com/cal-mag-dosage-calculator/)

## Provenance

- Model ID: `tyg-880`
- Model version: `1.0.0`
- Reviewed by: Umer Hayiat
- Page modified: 2026-08-24T08:35:31
- Runtime SHA-256: `e740a67ce9654421b58a3842f4daaa0aca1403290ec4beaa86867958a0f7abf1`

This Markdown document is a machine-readable mirror. The canonical interactive calculator is the HTML page linked above.