In 2023, late blight was present in parts of eastern Canada at levels not seen for several years, leading to a winter filled with late blight re-learning, and concern about potentially high primary inoculum levels in 2024. 

Some of the most important management practices include: 

• Early, preventative applications of fungicides with late blight activity. 
• Shifting to preventative applications of premium systemic products when late blight is reported in your region. 
• Early reporting of suspicious plants and/or identified cases, as late blight is easily spread with wind and rain to other potato fields, and other hosts.  

Think about the when and the why to maximize the benefits of different products in your spray program. For example, with Syngenta products: 

What (FRAC group)	Rate	When	Why
(29)	0.16 to 0.24L/ac	At flowering	Activity against late blight, but also white mold, which is higher risk at this stage
		Towards the end of the season, before top kill	Limits spread of spores, helping protect against tuber infection
(M)	0.9L/ac	Before row closure	Excellent coverage possible with a contact fungicide
		After flowering	Resistance management tool, plus activity against Botrytis
(40+49)	0.16 to 0.24L/ac	Before flowering	Excellent residual control and protection of new growth, even when disease risk is high
		After flowering
(40)	0.16 to .24L/ac	After flowering	Reliable, 10-day residual control

Remember that when fighting late blight, shorter intervals and systemic products are critical to help ensure new growth is protected.  

What about resistance management? 

A full toolbox is important for sustainable late blight management, so remember to follow resistance management guidelines as you plan a program. Did you know FRAC has tightened up the resistance management guidelines for Group 49-containing fungicides like Orondis Ultra?  

As of early 2024, the FRAC guidelines for foliar application in potatoes are as follows: 

• Do not make consecutive applications of a Group 49-containing fungicide; always alternate. 
• Make no more than two (2) applications of a Group 49-containing fungicide when the total number of applications targeting late blight is 5 or less. 
• Make no more than three (3) applications of a Group 49-containing fungicide when the total number of applications targeting late blight is 6-10. 

Always read and follow label directions. Orondis^®, Revus^®, and the Syngenta logo are trademarks of a Syngenta Group Company. Allegro^® is a trademark of ISK Biosciences Corporation.