Miravis^® Duo is an excellent tool for managing early blight (Alternaria solani) and brown spot (Alternaria alternata complex) and contains the Group 3 DMI fungicide difenoconazole, and the Group 7 SDHI fungicide ADEPIDYN^®. Group 7 fungicides like ADEPIDYN^® are at medium-high risk for resistance development, while pathogen risk for A. solani is medium and A. alternata is high. For resistance management purposes, FRAC considers all Group 7s to be in the same cross-resistance group. 


Summarized from FRAC Pathogen risk list, 2019. 

So, how do we extend the life of Group 7 fungicides as long as possible? Implementing fungicide resistance management strategies. Regional monitoring is one of many important tactics for resistance management. To catch up on other fundamentals of resistance management, check out this hub article.  

How local monitoring programs help 

For Group 7 fungicides and diseases like early blight and brown spot, the type of resistance is considered continuous. With use over time, populations gradually become less sensitive, meaning more fungicide is needed to achieve the same reduction in pathogen growth. 

Monitoring programs help identify shifts in sensitivity from year to year. Sensitivity shifts don’t mean there is field resistance. Sensitivity shifts provide an early indication of changes in the pathogen population before field resistance is observed.  

Monitoring shows sensitivity is shifting

In 2020 and 2021, the Syngenta field team collected potato leaves with early blight and brown spot symptoms from fields across Canada. Samples were processed at North Dakota State University (lab of Dr. Julie Pasche) and sensitivity to ADEPYDIN was determined for 100 isolates of A. solani (early blight), from 63 different fields.  

A key finding – slightly higher concentrations of ADEPYDIN were required to reduce growth in isolates collected in 2021 compared to isolates collected in 2020. In other words, there is evidence of a shift in Group 7 sensitivity. This means that, as recommended by FRAC, spray programs with Group 7 fungicides should be prudently planned.  

Ways to be prudent

Guidelines on the number of Group 7s in a foliar fungicide program depend on the total number of applications in the program. How soil and seed applications of Group 7 fungicides impact resistance is another consideration. There are no clear guidelines from FRAC on this in potatoes, but most Group 7 seed and soil applications would be considered solo applications because mix partners target other diseases. 

The prudent approach for Group 7 resistance management is to: 

• Include seed and soil applications in the total maximum number of applications in a season – this means if a Group 7 is applied on seed or in-furrow that the number of foliar Group 7s should be reduced by one. 
• Consider seed and soil treatment as a solo application within the foliar program. 
• Do not apply Group 7 fungicides consecutively when applied as a solo – this means if a Group 7 is applied to seed or soil, the first foliar application should not include Group 7 chemistry. 

Here’s a snippet of what a prudent approach looks like for a 9, 10, 11 or 12-spray program: 

Total applications in program	Maximum Group 7s recommended by FRAC		Maximum Group 7 applications using prudent approach
	Solo*	Mix	Soil**	Foliar
9-spray program	3	3	1	2
10-spray program	3	3	1	2
11-spray program	3	4	1	2
12-spray program	4	4	1	3

*Solo means Group 7 applied alone, or with a tank-mix partner that is ineffective against early blight and brown spot 
**Seed/soil application considered as a solo Group 7 application 

Looking for more on Alternaria? Refer to this hub article.

For more information including articles, resources and videos on resistance management, check out Manage Resistance Now. This is a collaborative effort of industry, academia and government experts, brought together by CropLife Canada, to raise awareness and promote the adoption of strategies to manage weed, insect and disease resistance.

Always read and follow label directions. ADEPIDYN^®, Miravis^®, and the Syngenta logo are trademarks of a Syngenta Group Company.