Editors note: This article was updated in October 2025.

When it comes to resistance management, the best long-term strategy is loss prevention. This means keeping the tools around for as long as possible. With all the jargon (groups, codes, risk, mode of action, etc.) around resistance management, is there a way to simplify how we think about fungicide resistance management in potatoes?

The Fungicide Resistance Action Committee (FRAC) has a great explanation of classification and mode of action. Click below to watch a short clip about mode of action groups, which they call “codes”, and labelling.

You know the code. Now what?

Plan a fungicide program that considers available products, including FRAC code and spectrum of activity, resistance management guidelines, label restrictions such as pre-harvest interval and re-entry times, secondary standards such as MRLs, and local knowledge of resistance and resistance risk. Stick to the plan as much as local conditions allow and participate in local resistance monitoring programs.

Here is another short video from FRAC, this time highlighting general best practices for resistance management:

What are the FRAC guidelines for early blight?

Guideline	Should it be applied in a mixture?	Should it be alternated?	Maximum number of applications in a program (solo)	Maximum number of applications in a program (mixture)
Group 3	Not critical	Not critical	No maximum, see label	No maximum, see label
Group 7	Recommended	Yes, if applied solo Max 2 sequential applications if applied in mixture	- 2 in a program with 5 to 7 early blight sprays - 3 in a program with 8 to 11 early blight sprays - 4 in a program with 12 early blight sprays	- 3 in a program with 6 to 10 early blight sprays - 4 in a program with 11 to 12 early blight sprays
Group 11*	Resistance confirmed in several regions of Canada.* Only use in mixture with an effective tank-mix partner.

Source: *Research led by J. Pasche at North Dakota State University using Alternaria solani isolates causing early blight on potato leaves collected in AB, MB, ON, QC, and NB, 2020-2021, n = 64 fields / 118 isolates. Performance evaluations are based on internal trials, field observations and/or public information. Data from multiple locations and years should be consulted whenever possible. Individual results may vary depending on local growing, soil and weather conditions. Always read and follow label directions.

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Syngenta offers several products that can help you manage early blight – and the risk of fungicide resistance – in your potatoes.

Guideline
FRAC Code	M	3	11	3	7	3	7
Resistance Risk	Low	Medium	High	Medium	Medium to high	Medium	Medium to high
Early blight	0.65 to 0.97 L/acre	0.23 to 0.4 L/acre		0.26 to 0.39 L/acre		0.4 L/acre
Maximum allowable applications on label	3	3		4 (2 by air)		3
Maximum number of early blight applications	3 (same as label limit)	See Group 3 and Group 11 FRAC guidelines (table above)		See Group 3 and Group 7 FRAC guidelines (table above)

Syngenta supports local monitoring programs to inform decision making. Testing provides an early indication of sensitivity shifts in the population before field resistance is observed. Survey results (2020-21) confirm a shift in sensitivity to Group 7 chemistry in the Alternaria solani (early blight) population found in several regions in Canada. As recommended by FRAC, spray programs that include any medium to high-risk modes of action, like Group 7 fungicides, should be prudently planned. For example, where shifts in sensitivity to Group 7 fungicides are reported, a more prudent approach is to count Group 7 seed or soil applications toward the total number of early blight applications in a program.

When to mix? When to alternate?

There is no clear evidence suggesting that mixtures or alterations is better for resistance management in multi-spray crops likes potatoes. As a result, the recommendation is often to both mix and alternate fungicide Groups. FRAC codes depending on resistance risk, label and secondary standard restrictions, and spectrum of activity. Mixtures help ensure implementation of a resistance management strategy while alternation provides flexibility in planning. Remember that mixtures are only effective for resistance management when both active ingredients effectively control the target pathogen.

Reach out to your Syngenta rep or retail partner if you'd like advice on building an early blight program that considers resistance management with your location conditions top of mind.

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