Mancozeb, the multisite potato blight fungicide, will continue to be available this spring. Its use will be necessary if the industry hopes to avoid further shifts in fungicide resistance, says crop protection manufacturer UPL.
The regulatory picture for the longstanding fungicide is challenging, with Mancozeb’s current approval expiring early in 2024. The active substance renewal is currently being assessed by the Chemical Regulations Division (CRD), but no conclusion is expected imminently. The uncertainty about whether it may be available this year meant some manufacturers were reluctant to risk being left with stocks. However, UPL committed to supplying mancozeb in 2023 to ensure that growers have the option to use it this season. “We have healthy supplies of straight mancozeb in the form of Manzate 75WG (mancozeb) and formulated with cymoxanil in Nautile DG (cymoxanil + mancozeb),” explains Geoff Hailstone, UPL’s potato technical expert. “It provides good activity on both Alternaria and late blight. Critically, it is cost-effective, persistent and has multi-site activity, making it an ideal tank mix partner. Manzate can protect the activity of other products, most of which are single-site fungicides with a higher risk of resistance or insensitivity developing.”
Fungicide resistance management is in focus this season with last year’s blight control failures associated with the spread of blight genotype EU_43_A1. It was first identified in Denmark in 2018 and subsequently accounted for 21% of samples in 2021 and 45% of Danish samples in 2022. 250 Samples taken from commercial fields and trials in 2022 were identified as control failures. Almost half of the isolates of EU_43_A1 collected between 2018 and 2022 were on the variety Kuras, which has a published high resistance to foliar and tuber blight, according to the European Cultivated Potato database.
“We rely on CAA-containing fungicides for about 50% of our blight programmes in the UK, so this news is very concerning. EU_43_A1 has not yet been discovered in the UK. However, the fact that we haven’t found it doesn’t mean it isn’t here. For this season, we must use precaution when planning our blight fungicide programmes,” explains Eric Anderson, senior agronomist at Scottish Agronomy.
“When building a fungicide programme, mixes of products from different mode of action groups are essential to protect crops and preserve the efficacy of these products for future seasons. The alternation between mixes is equally essential to prevent resistance from developing. In this context, mancozeb will be the tank mix partner of choice this season. Growers should avoid using products such as Shirlan (fluazinam), Ranman Top (cyazofamid), Revus (mandipropamid) or Carial Flex (cymoxanil + mandipropamid) without the inclusion of another at an effective dose and belonging to an alternative mode of action,” he said.
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