Potato Review

BP2019 12 POTATO REVIEW JANUARY/FEBRUARY 2020 Dr Cowgill said: “It’s thought there is a role in variation between aphid clones of the different species which we do not yet fully understand. Moreover, there are regional differences between the vectors and timing of transmission.” Aphid monitoring, carried out by trapping them in suction and yellow water traps, showed a peak in virus pressure and efficiency in virus transmission in 2018, with most of the virus pressure coming from M. persicae in some regions. The bird cherry-oat aphid (Rhopalosiphum padi) is also an effective vector of BYDV. “We also saw some population changes; incidence of the willow carrot aphid varies by region, but generally there is an upward trend of incidence with a blip in 2018.” Consideration has been given as to whether this may be a result of restrictions on the use of neonicotinoids, but the data from the yellow water traps don’t show direct evidence of this. One of the biggest challenges to controlling some of the important vectors is a decrease in sensitivity to pyrethroids. “Resistance monitoring is already being undertaken by researchers at Rothamsted, with funding from industry, AHDB and BBRO. They routinely screen M. persicae a to evaluate how sensitive the aphid is to various insecticides. “They also respond to suspected control failures and have shown in laboratory assays that both grain aphid and willow-carrot aphid have reduced sensitivity to pyrethroids. Mineral oils are widely used in virus management programmes elsewhere and AHDB-funded research evaluating the potential of mineral oils to minimise the spread of non-persistent viruses in potato seed crops in GB undertaken in 2015 found a reduction in potyvirus transmission compared with untreated crops. However, the work highlighted the need for awareness of local conditions when spraying. While no significant phytotoxic effects were found in Yorkshire or Scotland, more severe symptoms were found in Cambridge. This could have been a result of sunny weather during and after the application of the mineral oils, suggests Dr Cowgill, although yield issues were not detected as a result of the damage. Non-colonising aphids can create challenges for growers and spray programmes can potentially be overwhelmed when a large number of aphids fly in together. These aphids settle on crops, have a brief stay during which they may introduce virus into the plant, and then move on to other crops. “This is a real challenge for growers to deal with, as potyvirus transmission to a potato crop is really quick.” Reflecting on 2019 aphid flights, Dr Cowgill noted that in most locations in Britain the challenging numbers seen in 2018 were not repeated. “We acknowledge there is industry concern about aphid flights and we will continue to work with stakeholders to assess how to best address the challenges posed by aphids,” he said. Proper sampling key to detecting aphid and virus threats Testing for virus in potatoes can only be as good as the sampling method, warned Fera senior plant virologist Adrian Fox. Viruses are among the most economically damaging diseases affecting potatoes and can result in failure to obtain seed certification. Not only can aphid-vectored viruses cause yield losses of around 0.2t/ha, they can also trigger potato tuber necrotic ring disease from strains of PVY or tuber cracks from mosaics. Seed potatoes can pass on viruses such as PVY to daughter tubers, so any seed crops which may pose a risk are not permitted to be used as seed. Identifying any such infection, therefore, is key to protecting the ware industry.