Potato Review

www.potatoreview.com POTATO REVIEW MAY/JUNE 2023 21 DRY CLIMATE A year of two crops Higher risk of PVA and PVY in 2023 following dry season last year, say specialists. P REDICTIONS show that 2023 will be a year of two potato crops, according to Fera entomologist Larissa Collins. ose that have been irrigated or received su cient rainfall are likely to have thrived in the hot weather and could produce above-average yields of high-quality tubers. However, crops which have run out of water and senesced early will produce low yields of smaller tubers, probably with high levels of defects such as secondary growth, she said. While the e ects of the hottest day and the driest July on record dominated headlines last year, aphid monitoring by Fera through the rst half of the growing season suggested that potato crops could also be at much higher risk of virus diseases such as PVA and PVY, and that growers will need to be especially careful when selecting potential seed stocks. “Although the speci c numbers depend on where you are in the country, we have saw much higher aphid numbers than average across the UK,” said Larissa. “For example, we saw high levels of black bean aphid (Aphis fabae) and peach potato aphid (Myzus persicae). Levels of peach potato aphid have been several times higher than average peak levels in places, and willow- carrot aphid (Cavariella aegopodi) has also been recorded in high numbers.” is means that virus pressure has been much higher than normal, Larissa warned. e overall virus pressure in one region in May was 7½ times the average, and certainly the highest we have seen it since monitoring began in 2004. It is a similar story elsewhere. For example, in a more northerly region, which is a big seed production area, while virus pressure is much lower than further south, it is still 10 times the average level for that region.” Larissa says that these pressures highlight the advantages of e ective aphid monitoring when it comes to estimating virus risk for particular elds and potato stocks, particularly where they may be used for eld use. “We didn’t have a cold winter last year, so we started with high carryover populations, and then the mild spring and hot summer mean that aphid populations have increased accordingly. What happens to these populations in the autumn and winter this year will be heavily dependent on the weather.” Fera virologist Adrian Fox also warned that the high levels of aphids recorded mean that risks of non-persistent virus disease are particularly high. “Diseases such as PVY and PVA are picked up and spread so quickly by aphids that chemical control using insecticides often has little e ect on transmission rates,” he said. Integrated pest management, spray timing and product choice should be based on the species of aphid present and their populations, he said. Fera nematologist omas Prior said the dry weather could also see greater e ects from the damage caused by root-feeding nematodes. Larissa Collins, Principal Scientist of Enigma One and Entomology Team Leader. Fera nematologist Thomas Prior. “As the nematodes are feeding, they a ect the plant’s ability to take up water, so heat stress and early senescence are exacerbated,” he said. “Endoparasites are also likely to migrate into the host roots and consequently can have a higher impact in drier weather.”