Potato Review

www.potatoreview.com POTATO REVIEW September/October 2019 5 NEWS In such a challenging season for potato blight, application techniques have shown the potential to make a significant difference in preventing disease infection and maintaining a cleaner, greener crop canopy. Results of independent Eurofins trials in Derbyshire - maintained under artificially high disease pressure conditions and inoculated with blight strains in mid-July, along with natural infection - highlighted the strong performance of Revus and maindipropamid-based fungicides throughout the season. Speaking at the recent trials site open day, Syngenta Technical Manager Michael Tait reported on a trial to test intrinsic fungicide activity, where the same product is applied repeatedly on a plot throughout the season. That demonstrated Revus, along with mandipropamid plus cymoxanil or difenoconazole mixtures, provided consistently high performing results throughout the season, against all blight strains present. The best result, across the replicated trial plots, was where Revus was applied in mix with drift retardant Sterling. Independent assessment of the replicated plots in mid-August showed untreated plots had already been decimated by blight, with 98% of leaf area killed off. The Revus and mandipropamid mixtures, however, had retained the best green leaf area, with an average 14% infection, compared to 30% leaf area affected with mancozeb + cymoxanil and 32% infection with dimethomorph + zoxamide, for example. The Revus plus drift retardant was the best performing in the trial, with 88% of the green leaf remaining clean and healthy. Oxathiapiprolin was not included in the trial, by industry agreement not to expose the fungicide to potential resistance issues resulting from repeated applications. Research has shown the drift retardant can influence the spray pattern of conventional flat fan nozzles, to reduce the number of ultra-small drift susceptible droplets, and concentrate more in the desirable mid-sized droplet range to target the potato leaf and canopy. Syngenta Potato Science trials at the Eurofins trials site had, for the first time, featured tractor-sprayed plots, designed to replicate field conditions and to evaluate the potential for 90% drift reduction technology for blight applications. “The results have shown how well farm practice can perform, compared to the blight trial sprayer using conventional flat fan nozzles,” said Michael. “The Revus, and particularly Revus plus drift retardant, plots were virtually clean of any infection, despite having been inoculated with the same blight strains and managed under conditions conducive to blight.” The ‘industry-standard’, using the angled Syngenta Potato Nozzle, alternated forward and backward along the spray boom, performed exceptionally well, and the new designs of 90% drift reduction nozzles tested – including a Lechler IDTA and an innovative Syngenta 90% DRT development nozzle – achieved comparable results. With blight infection at 82% in untreated plots by mid-August, applications of Revus with the Syngenta Potato Nozzle and both 90% drift reduction nozzles had protected the adjacent plots at just 3% infection. Where Revus + drift retardant had been used with the Potato Nozzle, the infection rate was less than 1.5%. “This initial trial has shown the potential that can be achieved, with further ongoing research into where and when the 90% drift reduction technology could help potato growers and sprayer operators to maintain timely blight programmes,” said Michael. Blight trials target application techniques Dessication trials findings FMC’s demonstration plots at Potatoes in Practice this year showed the contact potato desiccant Spotlight Plus, when applied twice, performed well as part of programme, particularly in a flail and spray situation but, when applied as part of a foliar only application programme at seven- day intervals, there was a clear difference in performance. This was noticeable in terms of overall desiccation when comparing 300 litre to 450 litre of water with the later rate noticeably more effective. The best performing plot on FMC’s site was the mix of Spotlight Plus with Gozai (pyraflufen- ethyl) and Ranman (cyazofamid) applied twice using the maximum total dose of each product applied seven days apart. FMC agronomy manager Jeff Fieldsend said the performance of this sequence was comparable to two applications of diquat. “The result was very encouraging and applications were made onto a plot of Maris Piper which was flowering at the time of application, so you could say this was a stiff test.” As yet however this mix is not supported by either manufacturer as further work needs to be carried out to ensure there are no issues concerning tuber quality such as skin set, vascular browning or in fact yield. Jeff said, following flailing, stems should be allowed to wilt and dry for 24 hours prior to application of Spotlight Plus at a rate of 1.0 l/ha in a minimum of 300 l/ha water from mid-morning to mid-afternoon. A follow-up treatment might be required at a rate of 0.6 l/ha, five to seven days later. • For further details on Potatoes In Practice 2019, turn to page 40.