Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2022 11 PEST OUTLOOK Institute found that 40% of the sampled late blight population were 36_A2, and although this is an aggressive strain, but has no known insensitivity to any of the fungicide groups. As such, while growers may need to use their arsenal to the best effect, they do not need to avoid any particular actives when it is identified in their area. The formerly dominant strain 6_A1 (Pink 6) was reduced to 24 percent across the country, but in the Hereford area where Andrew is based, it is usually the first one to come into the crop each year. “There are some varieties that are particularly susceptible to 6_A1, such as Taurus and Lady Rosetta, so when deciding on the order in which fields should be sprayed, they should be prioritised. I used to use Shirlan ( fluazinam) at rosette stage, but because of the threat from 37_A2, for Late blight toolbox: ‘Use it to its full extent’ Based in Herefordshire, Andrew has been working for Hutchinsons for 16 years and looks after nearly 8000 ha of farmland, ranging from Cirencester, to the Welsh borders, south Shropshire andWorcester. Andrew Goodinson , Agronomist and Potato Specialist at Hutchinsons, offers seasonal insights into late blight (Phytophthora infestans), early blight (Alternaria alternata and A. solani) and aphids. G ROWERS should not lower their guard when it comes to late blight control, and should invest in a range of actives that can be applied according to the conditions and stresses present when Hutton Criteria are triggered, Andrew Goodinson has stated. Genotyping undertaken at the James Hutton Institute identified increased incidence of new blight strain 36_A2 to 36 percent of outbreaks in England, whilst fluazinam-insensitive 37_A2 ( formerly known as Dark Green 37) was less prevalent than in 2020. Its previous rise caused alarm bells to sound across the sector, resulting in growers reducing the use of fluazinam in their blight control programmes to ensure resistance management. However, this resulted in an increase in costs. Andrew said: “Now that 37_A2 is on the wane, fluazinam can responsibly be re- incorporated into programmes again. However, it should only be used at full rate (400ml/ha) mid-programme and growers need to be careful not to select for 37_A2 by using it on its own. “For example, fluazinam can provide important cost-effective benefits as part of a mixture with other actives such as mancozeb. It has other benefits, too, for example it can also help keep on top of Botrytis cinerea which can infect stems and leaves during flowering. “ At GB level, in 2021, the James Hutton the last two years we have amended our strategy and have found Ranman Top to fit in well at this stage,” Andrew said. Andrew also likes to include Proxanil (cymoxanil and propamocarb) in his programmes because of its suitability throughout the season, noting that it is persistent, systemic and moves well in the plant. It also offers some curative activity. Most fungicides only provide protection from infection and very few of the currently available actives offer curative activity. Growers need to act before infection takes place. Spray intervals and mixes Moving on to talk about spraying and spray intervals, he remarks that he finds the Hutton Criteria to be a useful guide for product choice, if slightly too sensitive. That said, even if blight pressure is low, ➜ Alternaria leaf tissue monitoring at NIAB. Photo: Syngenta