Last month, following a review into the active substance mancozeb, HSE proposed to withdraw approval of the chemical in Great Britain. For growers up and down the country, this was a major blow. Products containing mancozeb - like MANZATE 75 WG and NAUTILE DG - have long been a vital weapon in the fight against potato blight, thanks to mancozeb’s multi-site activity for resistance management. As the only multi-site approved, it’s used multiple times in a programme. What should growers expect moving forward, and how will resistance programmes handle the mancozeb withdrawal? Let’s take a look.
Why has Mancozeb been withdrawn?
HSE conducted a review of the approval of Mancozeb Article 21 of retained Regulation (EC) 1107/2009. It allows HSE to initiate a review of any part of the approval of any pesticide active substance, whenever new scientific evidence emerges.
If new data comes to light that indicates a substance may no longer satisfy the criteria for approval, HSE can act.
Despite evidence submitted by UPL and many other organisations in support of mancozeb, the HSE concluded it does not meet the required criteria and proposed to withdraw approval.
When do growers need to stop using products like Manzate 75 WG and Nautile DG that contain mancozeb?
Right now, we don’t know for certain. UPL, suppliers and growers are all waiting for confirmation on final withdrawal timelines.
Based on the current proposals, we expect:
The sale and supply of any plant protection product containing mancozeb to end on 31st October 2024
The disposal or use of mancozeb products to be completed by October 2025
It’s important to note these are the current proposed timelines by DEFRA, and are subject to change. They can only be finalised at the end of the WTO consultation process, which should be complete by early spring.
Member countries and stakeholders will discuss the withdrawal at this consultation, and their feedback could impact the final timelines.
We will of course keep you informed when these timelines become concrete.
How should growers build their blight programme in 2024 and beyond?
“Plan and purchase your usage accordingly to avoid any disruptions to your planned blight programme,” says Geoff Hailstone, UPL UK’s potato technical lead.
As it stands, Mancozeb will still be available for sale this season and can be applied as usual.
“Given the current proposed times, we plan to have all our UPL products containing mancozeb - MANZATE 75 WG (Mancozeb) and NAUTILE DG (cymoxanil + mancozeb) available this year,” says Geoff.
UPL are currently talking to the market and liaising with suppliers to determine how much mancozeb is likely required to support growers and their blight programmes.
The advice right now, adds Geoff, is to “speak with your suppliers and share what you need. This greatly helps our production planning and will make sure you get the required products.”
While this year - and potentially next - will still have mancozeb as an option for blight control, what do future years look like?
Adapting to blight control without mancozeb
“There’s no doubt about the value of mancozeb in helping to manage blight outbreaks and prevent the development of fungicide resistance,” says Geoff. “You only have to look at the outbreaks in Belgium and Holland in 2023 - where mancozeb has been unavailable for several years - and compare with the control achieved in the UK during that same period.”
The rise of blight strains resistant to the carboxylic acid amide (CAA) group of fungicides is a threat. Mancozeb has helped the UK avoid a breakdown in control so far, but without it, what does Geoff advise?
“Keep following general FRAC guidance. Always mix products with different modes of action in the same application and alternate mixes in the programme.”
The current FRAC CAA working ground use recommendations are:
Apply CAA fungicides preferably in a preventive manner
Apply CAA fungicides always at recommended dose rates
Apply a maximum of 50% of the total number of intended applications for disease control not exceeding a total of 4 CAA fungicide sprays during one crop cycle. In areas of high resistance, the total number should not exceed a maximum of 3 applications during one crop cycle
Always apply CAA fungicides in mixture with effective partners such as multi-site or other non-cross resistant fungicides
An effective partner for a CAA fungicide is one that provides satisfactory disease control when used alone at the mixture rate
Alternation with fungicides having other modes of action is recommended in spray programmes.
Making good use of PROXANIL
Geoff also highlights the rising importance of PROXANIL.
“Look to PROXANIL, with its two actives cymoxanil + propamocarb, which have no reported resistance issues.”
The benefits of cymoxanil include a very low risk of developing resistance and kickback activity. Propamocarb, the only active in the carbamate resistance group, has good plant movement and strong anti-sporulant activity.
“Tank mix with a protectant fungicide like cyazofamind,” recommends Geoff, “it strengthens the activity.”
That way, PROXANIL should deliver excellent resistance management at a time when growers need it most.
