UPL has announced that mancozeb, the multisite potato blight fungicide, will continue to be available this spring, and states that its use will be necessary to avoid further shifts in resistance.
The product’s current approval expires in 2024, with its active substance renewal being assessed by the Chemical Regulations Division (CRD).
This uncertainty left many suppliers reluctant to be left with stock, however, UPL has committed to supplying the fungicide in 2023 so that growers continue to have options.
“We have healthy supplies of straight mancozeb in the form of Manzate 75WG (mancozeb) and formulated with cymoxanil in Nautile DG (cymoxanil + mancozeb),” said 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.”
Resistance in focus
Last season’s blight control failures have been associated with the spread of genotype EU_43_A1, which 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 EU_43_A1 collected was on the variety Kuras, which has a published high resistance to foliar and tuber blight, according to the European Cultivated Potato database.
The genotype was also detected in the Netherlands and Belgium in 2022. Researchers at the University of Aarhus and James Hutton Institute analysed important potato regions in Jutland and found that the first five isolates were entirely resistant to mandipropamid.
EU_43_A1 is the first strain of P. infestans reported to have resistance to a carboxylic acid amide (CAA) fungicide.
“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,” explained 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.
“Another consideration is Alternaria control. Several fungicides that control Alternaria are in co-formulation with a CAA-containing product. Unless the variety has good resistance to the disease, mancozeb will be useful in suppressing Alternaria. I would advise applying 1,000g a.i/ha of mancozeb alongside a mixture of single-site chemistry,” added Mr Anderson.
New products are expected to be launched in 2024, which will add to the armoury. In the meantime, UPL expects mancozeb to be a valuable tool to control disease in 2023.
For more information go to www.upl-ltd.com
