A ProCam agronomist has said the key to reliable blight control is to adapt programmes according to weather conditions and using forecasting tools to determine when the threat of blight is at its highest.
The agronomy and crop protection business ProCam said potato growers will have to modify their blight protection programmes with the withdrawal of mancozeb coming into effect.
Mancozeb is a multi-site fungicide ingredient that controls potato blight and its approval expires on May 31, 2024.
The final date for sale and supply of mancozeb products is November 31, 2024, with the final storage, disposal and use-period ending November 31, 2025.
ProCam said that, although alternative active ingredients are available, the rules and regulations surrounding their use and application intervals are not entirely straightforward and are further complicated by confirmed cases of resistance to some key actives on the continent.
ProCam agronomist Harry James said: “For example, instead of being able to apply three consecutive applications of CAA (carboxylic acid amide) fungicides, the latest FRAC (Fungicide Resistance Action Committee) guidance is that these should now be limited to a maximum of two consecutive applications.
“That’s a sensible recommendation based on the loss of efficacy of this group of fungicides on the continent, with crop protection manufacturers such as Syngenta going a step further by advocating the use of mandipropamid in alternation with fungicides with a different mode of action.”
Resistance
Resistance to oxathapiprolin (Zorvec) has also been confirmed in some parts of northern continental Europe including the Netherlands, Belgium and Germany, with the post-Zorvec application interval being reduced from 10 days to seven as a result.
It must also be used in alternation with a non-CAA chemistry, ProCam said.
“This will make it more labour intensive and time consuming to keep crops clean, especially as this key active no longer provides a curative effect,” James said.
“Instead, it can only be relied on to deliver preventative activity which means sprays will need to be applied on time every time in order for crops to remain protected.
“To avoid any confusion that the new rules might introduce, and to ensure they don’t fall foul to the same resistance woes that their European counterparts are already dealing with, UK potato growers should seek professional advice from their agronomist to help them devise a suitable blight programme for this season and beyond.”
ProCam said growers should also be aware that although fungicide resistance has not yet been confirmed in UK crops, the risk remains high and is further escalated by the shortfall in British seed potatoes.
This means there is a risk of resistant strains being introduced by imported seed stock.
“The high incidence of foliar and tuber blight in continental seed crops means there’s a very real risk of resistance affecting British crops,” James said.
“For that reason, anti-resistance strategies – alternating modes of action and limiting the exposure of any single active – must be followed from the outset.
“Keeping a close eye on resistance updates throughout the season will be essential, as will taking professional advice to devise a suitable spray programme, not least because the ever-changing legislative position and evolving resistance situation will make keeping abreast of the latest rules that much more complex.”
With careful planning, James aid growers and their agronomists should still be able to achieve good levels of blight control and stay ahead of the threat of resistance.
“It must be stressed, however, that the key to reliable control will be to adapt programmes according to weather conditions and to use forecasting tools to determine when the threat of blight is at its highest.
“Cultural controls, such as selecting varieties with better natural blight resistance, and taking extra care to remove volunteer potatoes from dumps and other crops in the rotation should also be factored into the equation.
“Nothing, however, will beat getting into the field and putting boots on the ground to assess the crop, the severity of disease pressure and if a blight infection has occurred.”
