Potato Review

www.potatoreview.com POTATO REVIEW JULY/AUGUST 2020 13 DESICCATION AND FLAILING is less critical at Bannister Farms where crops are destined for the packing market via long-term storage. “Skin set is so important for our crops ahead of storage and they need at least seven days following spraying before lifting into store anyway,” said Tom. “For those who need to lift crops according to market demand, its harvest interval could be very useful.” After several years’ experience with ail and spray at Bannister Farms, Tom has not had to apply any additional chemical to desiccate crop stems. However he suggests that potato herbicide Gozai (pyra ufen) could be added to the desiccation sequence in scenarios when a topper cannot be used. “ e only problemwith Gozai though is it’s following crop restrictions, which determine that you have to plough, and this is something we try and avoid doing after potatoes because it can encourage volunteers in the next crop. “It’s better that volunteer potatoes are left on the surface to be degraded by frost. Our established ail and spray operation on the farm is very e ective at being able to stop crop growth quickly, giving us more control at this important stage of the season in setting up the crop for long- term storage. And it also means we don’t have to run toppers on the harvester, allowing operators to solely concentrate on the lifting process.” Flail and spray must be the go-to system but non- ail desiccation still an option for growers Having assessed results on a number of industry trials and following work with his own growers during the past three years, Drem-based Agrii agronomist Andrew Sprunt reckons a ail and spray approach de nitely o ers growers the quickest and most reliable approach to stem desiccation, but stresses the importance of using the correct ail and set up. “As most are three-bed ails, the use of GPS at planting can be bene cial to getting the ail set-up and help deliver the right desiccation outcome at harvest,” he said. Andrew said growers should try to ail in dry conditions, to minimise disease spread such as blight or blackleg, and apply a protoporphyrinogen oxidase (PPO) inhibitor herbicide such as Gozai (pyra ufen- ethyl) in bright, sunny conditions within 48 hours of ailing using high water rates (at least 300L/ha) to ensure good coverage. “I recommend ailing the plants to leave around 20cm of exposed stem and applying Gozai + oil around mid-morning when stem pores are open and more receptive,” he said. However, despite a strong preference for ailing, Andrew also recognises the need amongst some growers for a reliable non- ail approach that becomes viable when combined with careful forward planning on use of nitrogen and irrigation. “I have seen some good trials, most notably from the SAC and the agrochemical manufacturer BelchimCrop Protection. Both have proved that it is possible to achieve good results using a chemical-only approach, although to achieve the end result will take longer than ailing and may cost more. For seed, salad and big green foliage main crops I would de nitely not recommend it,” he said. For those going down the chemical-only route for the rst time this year, Andrew believes that the variety being grown, combined with careful management of nitrogen rates plus some timely dry weather, will enable the crop to get to a natural tipping point where it begins to senesce. But it won’t be straightforward and advanced planning will be needed. “Trials have shown that determinate varieties such as Estima, Maris Peer and Charlotte are easier to work with as their crop canopies are already starting to senesce before burn down begins. However, with later indeterminate varieties such as Royal and Cultra, growers will need to manage the canopy in preparation for applying the PPOs. “Both the PPO inhibitors (pyra ufen-ethyl e.g. Gozai, and carfentrazone-ethyl) are pretty equal on performance in my opinion and growers will need to use both in a sequence of up to four sprays (maximum 2 applications per product) to desiccate the more di cult indeterminate varieties. Critically growers won’t see browning of leaves as they did with diquat so the key will be to keep water volumes high and spray well into and under the crop canopy to reach plant stems, stagger the timing of the sequences well enough apart, be patient and trust the PPO’s to do their job.” Technical Account Manager for Belchim Crop Protection in Scotland, Russell Whiteford, has recently been involved in trial work comparing tuber sizes from chemical- only strategies with tubers resulting from di erent desiccation systems. “Last year Belchim did a joint trial with Scotland’s Rural College (SRUC). During that trial we looked at tuber size fractions and yields across a range of desiccation methods. Broadly speaking, the key point is that the nal test dig revealed that the size distribution and yields of the tubers were the same regardless of the desiccation strategy being used. All main desiccation options were covered including diquat followed by ail followed by Gozai plus oil, diquat followed by Gozai with no ail and various other chemical combinations excluding diquat but including both Gozai and carfentrazone- ethyl applied in varying sequences,” he said. “From this we concluded that no matter what desiccation strategy you apply to the crop, the rst phase of that treatment will initiate the crop to senesce. ereafter, it’s a case of killing the haulm and getting good skin set so the tubers are easier to harvest. e AHDB con rmed our ndings in trials of their own last year.” “If the grower already uses a flail to top the haulm and continues to use in combination with a PPO inhibitor, then the cost increase is less significant.”