Mathuresh Singh, director of Agricultural Certification Services (ACS) in Fredericton, observes PVY expression in potato plants grown from secondary infected tubers in the ACS lab. foliar symptoms, he says, but in three susceptible varieties (Yukon Gold, AC Chaleur and Envol) it can cause necrotic tuber lesions or rings that can make the entire crop unmarketable. Singh notes that the PVY NTN and PVY N:O/Wi strains exhibit distinct and typically cryptic symptoms compared to PVY O , which can make them more difficult to identify in the field. As a result, rogueing operations to manually remove infected plants from the field during the growing season are often less successful, he says, as are traditional seed certification techniques such as visual inspection during the crop growing period and winter grow-out of seed samples. Best management practices The study does include a number of recommendations for helping seed potato growers fight PVY by targeting the insects that carry the disease. According to Singh, PVY is transmitted by more than 50 aphid species and an abundance of aphids in potato fields has been shown to significantly increase PVY spread. “Since the disease is spread by so many species of aphid, it’s very hard to manage,” Singh says. The study’s best management practices for controlling disease-carrying aphids involve a combination of mineral oil and insecticide spraying that acts to minimize the on-farm spread of PVY in seed potato operations. Under the PVY research program, different spray programs were tested through field experiments that took place in New Brunswick and Manitoba from 2014 to 2016. Results of the trials were published in the American Journal of Potato Research in 2017, and they’ve also been widely presented at numerous potato conferences and grower meetings in Canada and the U.S. “Our trials were conducted … in two very different potato growing regions of Canada, yet the results and recommendations from them are consistent and thus should be generally applicable across the country,” Singh says. According to Singh, frequent mineral oil spraying that starts early and continues season long, supplemented often with insecticides in a simultaneous spray, has shown the greatest potential. “We recommend that as soon as you can see green leaves coming out of the ground, you should start protecting those plants,” Singh says. He adds if growers wait until later to begin mineral oil or insecticide applications, the disease may already be present and spreading in the field and their PVY management practices won’t be as effective. Singh notes processing potato operations aren’t permitted to spray mineral oil, so the best defence for them is to plant certified seed that’s either PVY-free or has extremely low levels. “The first strategy is starting with clean seed,” he says. “If there is no PVY, there is no inoculum that can spread the disease, even if you have a lot of aphids.” Another recommendation is for growers to start rogueing early, especially in tractor rows subject to mechanical PVY transmission, in order to remove sources of inoculum and prevent in-field PVY spread. Singh adds early top killing of potato plants will help prevent late season disease spread. Crop rotation, border crops and management of volunteers are also recommended as best management practices for controlling PVY. According to Singh, the PVY research project has already had a significant impact within the potato industry. “It’s been very successful,” he says. Singh notes that the mineral oil or insecticide approach advocated by the study has not only resulted in a sharp reduction in PVY in New Brunswick but has also helped producers in other provinces get a much better grip on the disease. “I would say in general, PVY is in a declining trend,” Singh says. TOP CROP MANAGER/POTATOES IN CANADA | Spring 2018 17 PHOTO COURTESY OF AGRICULTURAL CERTIFICATION SERVICES.