Key reasons to rotate your botrytis fungicide groups
The pathogen botrytis cinerea is classed by the Fungicide Resistance Action Committee (FRAC) as being high risk for gaining resistance to fungicides.
This fact makes it even more relevant to focus on having a long-term plan.
When it comes to protecting grapes from botrytis the choice of fungicide groups is quite limited, especially when compared to other grapevine diseases such as powdery mildew.
There are eight fungicide groups listed in the AWRI guidelines “Dog Book” for botrytis management in export wine grapes (Groups 17, 9, 11, M5, 12, U1, M and 44).
Therefore, it’s critical to the overall strategy to combine good vine management with a sound resistance strategy whilst rotating fungicide groups within the season and from year-to-year.
For growers in medium to higher risk areas that spray at or around 80 percent capfall and then again at EL-29 (4 mm berry size) the chemical rotation tends to occur by default.
Many choose the Group 17 Fungicide, Teldor®, for the early timing and follow with Groups 9 and 12 in the product SWITCH®.
This makes sense as Teldor can’t be used past 80 percent capfall.
SWITCH is known by many in the industry as the ‘go-to’ product for the later spray, with the ability to be applied up until EL-29.
Growers in ‘low risk’ areas often have a different approach to botrytis management and focus on the 80 percent capfall spray timing and don’t plan to apply another key botryticide later.
Planning to rotate fungicide groups from year-to-year makes for sensible planning for growers with this strategy.
Reliance on just one or two fungicide groups for this early spray timing year-after-year will accelerate the likelihood of the pathogen gaining resistance to that group or groups.
Unfortunately, I still occasionally come across comments like, ‘it works well for me, so I’ll continue to use it; if it breaks, then I’ll change groups’!
The reality is, there is no lineup of new chemistry coming through the system to replace such ‘broken’ fungicide groups, so we need to always plan to preserve existing groups for as long as possible.
With planning, growers need to remember that Teldor and Prolectus® are both from the same Group - 17. SWITCH and Scala® both contain Group 9 fungicides.
SWITCH also has a Group 12 component which of course benefits a resistance management strategy.
Again, prevention is better than cure. Plan to hit hard and hit early, before any infection becomes established.