Potato Review

24 POTATO REVIEW NOVEMBER/DECEMBER 2020 FUNGICIDE TREATMENTS and how to apply storage treatments within the limitation of the farm’s system. Ideally, seed should be treated on a roller table prior to storage, but because almost all crops are harvested into boxes and placed straight on a drying wall, this rarely happens in practice. Paul and David say the next best scenario is to treat at rst grade – typically November or December –with either Gavel (imazalil) or Storite Excel (thiabendazole), or amixture of the two. ere are di erences in activity on the four Fusarium species that cause dry rot, with F. sulphurium populations resistant to thiabendazole. Silver scurf and skin spot also show some resistance to the active. Only low levels of resistance to imazalil exist in Fusarium avenaceum, with the active ingredient remaining very e ective against all other Fusarium species, plus gangrene, skin spot and silver scurf. Antagonism between the two products should be considered when mixing. Storite Excel has to be put in the tank before Gavel and agitation switched on throughout the application process. Used as a single product, Gavel has broader activity and is an easy formulation that is ideal for more di cult application situations and older type applicators. Updating older spray systems improves performance While an older roller table applicator can still perform well if correctly set-up and maintained, growers applying liquid storage treatments are advised to update kit to achieve the best results and operator and environmental safety. Many farms still use static hydraulic nozzles or spinning disc applicators, but work carried out at AHDB’s Sutton Bridge Crop Storage Research facility suggests these only achieve 53% and 46% coverage of tubers, respectively. In contrast, a twin rotating nozzle setup like Team Sprayers’ CTC 2 has been shown to achieve 76% coverage, dramatically improving performance of the fungicide applied. Big strides have been made by British seed growers and merchants recently, with many moving to Team’s CTC 2 or similar. is has the additional bene t of completely enclosing the treatment area to eliminate spray drift to the grading shed. Consider convenience of direct injection systems Some larger producers aremoving to direct chemical injection for roller table application. is route is highly recommended andwith the best new grading lines costing £300,000-£400,000, the additional £1,500 per direct injection unit is considered insigni cant. A direct injection systemallows the operator to ll multiple chemical hoppers, typically up to four, with neat fungicide, which is then fed directly into the pressurised spray line. ese systems use lowmaintenance peracetic pumps to deliver the product, which ismuchmore accurate than the conventional method of mixing spray solution and delivery via a piston diaphragmpump. Withmany still wanting to apply the two active ingredients of former Storite Super (imazalil + thiabendazole, direct injection takes away the highlighted risk of antagonism. It also allows multiple chemical hoppers to be used for di erent products, allowing easy and clean switching betweenGavel and Storite, or later applications of pre-planting treatmentsMaxim ( udioxinil) or Rhino ( utolanil). Like the CTC 2, direct injection limits operator exposure as nomixing is required. In addition, if the grading and application process has to stop, there is no solution left requiring agitation until it is used up. Despite the advantage of direct injection, conventional systems still do a good job. In any newpurchase of a conventional system, consider the size of tank andmatch it to average daily throughput to avoid having excess solution left over at the end of a shift. Most systems will require nomore than 90-100 litres. “Some larger producers are moving to direct chemical injection for roller table application. This route is highly recommended.” Position the spray system close to the application area to limit pipework and any associated pressure drop. Photo: Tim Scrivener A TEAM CTC 2 applicator and variable speed roller table oer producers the best tuber coverage when using liquid fungicide seed treatments. Photo: Tim Scrivener