Potato Review

www.potatoreview.com POTATO REVIEW JULY/AUGUST 2021 45 DESICCATION “For the fourth key area we need to return to the PPO application. It’s important that growers always apply PPOs in minimum water volumes of 300l-400l/ha to ensure good coverage. For the fth and sixth keys, I would highlight both nitrogen management to control haulm size and understanding if the variety being grown is determinate or indeterminate which often dictates the nutrition management strategy” adds John. In terms of desiccation methods, John believes a ail approach followed by 1 or 2 PPO applications is the quickest and most economical approach, providing the grower has the right soil type and weather conditions for successful ailing. “My advice is to do no pre-sprays prior to ailing and, when ailing the crop, leave 15-30cm of exposed stem behind with any foliage completely separated from stems. Flailing is then followed up by an application of Gozai (pyra ufen-ethyl) at its full rate of 0.8l/ha + methylated vegetable oil alongside an application of Ranman Top (cyazofamid) to give the crop on going tuber blight protection through desiccation whilst killing any remaining zoospores post ailing. “When desiccating seed crops I would also recommend going back into the crop with a second spray of Gozai + oil, again at 0.8l/ha, 10 days after the rst PPO was applied to make absolutely sure there is no stem regrowth. If growers are unable to ail due to poor weather or soil type then, on a chemical-only strategy, I would recommend Gozai over carfentrazone-ethyl as the rst spray in the sequencing. Mainly because I feel that it is more e ective in opening up the crop. On prevention of regrowth there is no discernable di erence in the performance of the 2 PPOs based on the trial work and customer feedback I’ve received,” said John. Process challenges Calum Cargill of Crop Services (Scotland) Limited advises on 810ha of potatoes per annum covering Perthshire, Angus and Fife where 85% of his customers are certi ed seed growers. Calum rst began early desiccation trial work combining ailing with the use of Gozai as his rst choice PPO in 2016, not long after the product was launched. “I de nitely feel that I know more now than I did ve years ago. But, whilst desiccating ware crops is often pretty straightforward in reasonable weather conditions, many of the original issues that I came up against when desiccating seed crops are still signi cant challenges today, despite my increased knowledge base. “Seed crops are young and even when tubers reach their target size they want to keep growing. Regardless of whether the desiccation approach is mechanical or chemical risk of virus transmission by aphids and strong possibilities of stem regrowth can make the process very challenging. “A chemical-only strategy is certainly possible on seed crops but it’s expensive and can take a number of applications to complete the process. Flailing rst is certainly quicker, however growers require a reasonably dry weather window to ail e ectively. Even in August, this far north that’s not always possible” he adds. Whilst Calum is not a keen advocate of nitrogen management, sacri cing the bene ts of a bigger potato crop for potentially easier desiccation, he accepts that, in some situations, a compromise is often unavoidable. “In dry conditions and, on anything but very light soils, my general advice to customers would be to ail and follow up with a PPO such as Gozai at its full rate of 0.8l/ ha + oil. If it’s a seed crop then growers must be decisive and, once tubers have reached their target size, a decision to kill the crop should have been made at least 5 days before hand. Flail well to ensure clear separation of foliage and exposed stems, then apply the PPO 24-48 hours later in bright, sunny conditions if possible to maximise its e ectiveness. “Of the 2 PPOs available to growers my personal choice would be Gozai, based on the excellent technical support and advice I receive from Belchim’s technical team. However, when employing a chemical-only strategy both available PPOs must be used in sequence to maximise results,” said Calum. “My advice is to do no pre-sprays prior to flailing and, when flailing the crop, leave 15- 30cm of exposed stem behind with any foliage completely separated from stems.” John Sarup, SPUD Agronomy “Whilst desiccating ware crops is often pretty straightforward in reasonable weather conditions, many of the original issues that I came up against when desiccating seed crops are still significant challenges today, despite my increased knowledge base.” Calum Cargill, Crop Services (Scotland) Limited