Potato Review

www.potatoreview.com POTATO REVIEW JANUARY 2022 25 TUBER CARE Results from these tests will also help inform growers of the need for a pre-planting seed treatment, which is highly effective at minimising the impact of the disease. “We are moving towards a situation where we’ll have to justify the use of chemical control measures with much more detail, which is the right thing to do. Testing can help do that,” said Kyran. Invisible threat Matt Back at Harper Adams University, who is an expert in the control of Rhizoctonia in potatoes, points out that buying certified seed from a reputable source has an important role in the integrated control of any disease. However, the various tolerances to black scurf in the seed potato classification schemes in Scotland and England and Wales means there can be no guarantee that the seed will be completely disease free. This is important because even low levels of seed borne Rhizoctonia can result in significant stem and stolon infection after the crop is established. Matt says an added complication is the variation in anastomosis groups (AGs) of Rhizoctonia solani present in the UK, with one of the dominants being AG21, which is barely detectable by visual inspection. It is known that AG21 is a major cause of stem and stolon canker but does not readily produce sclerotia or black scurf on tubers, so is an “invisible threat” to be aware of. “There were cases last season where growers didn’t pick up any symptoms in the seed and still ended up with significant disease. “If you were being ultra-careful, on top of any visual inspection [ for black scurf caused by infection by other anastomosis groups], getting seed tested in a lab to check for presence of AG21 is a good idea,” said Matt. Liquid treatment Paul says that in the recent past growers have been relaxed about making last minute decisions on whether to use an on-planter powder seed treatment or not. However, where risk assessment is carried out early and there is a need to treat, he now recommends that seed buyers ask their supplier to apply a liquid seed treatment before delivery. This will not only ensure that seed borne Rhizoctonia is well controlled, but also take a job off the planter operator, who can concentrate on the many other aspects of the planting process. “With costs of production going up, there is a real need to minimise waste and maximise marketable yield and Rhizoctonia has a serious and negative impact on both. “You shouldn’t grow anything you can’t sell, and a liquid seed treatment is a solid investment that helps ensure you maximise returns and ease pressure at planting,” he said. There are currently two liquid options for Rhizoctonia control on the market: Rhino ( flutolanil) and Maxim ( fludioxanil). Rhino is the only product that can be used on seed, ware, and processing crops, and with full control of both black scurf and stem canker on the label. Paul says that where Rhizoctonia is dominating decision making, the flutolanil- based product is the best option. “It is a good product and, in my experience, slightly superior to others on black scurf and stem canker in particularly difficult situations.” Coverage key Whichever product is chosen, Kyran stresses that as with storage treatments, Black scurf in Gemson. Obvious black scurf is not the only sure-fire way of detecting disease on seed tubers, as some Rhizoctonia solani anastomosis groups like AG2-1 are barely evident through visible inspection. Photo by Eric Anderson/Scottish Agronomy “We are moving towards a situation where we’ll have to justify the use of chemical control measures with much more detail, which is the right thing to do. Testing can help do that.” Kyran Maloney, SAC Consulting. ➜