Tyler D. B. MacKenzie,
In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, processing and tablestock potato fields in New Brunswick, Canada between 2010 and 2014. These represented 13 potato varieties, managed by 16 growers employing a wide range of PVY control techniques. Many aspects of management techniques were quantified, as well local aphid abundances and climatological data. PVY spread, measured in leaves and tubers (by ELISA and RT-PCR), was tracked through the season in individually marked plants. Over the five seasons under study, on-farm PVY spread overall has declined substantially. Across all 56 fields, however, it has varied widely, from 10 fields not showing any spread during the crop season, up to as high as 76 % spread in one 2012 field. Factors correlated with increased PVY spread included seed-borne PVY inoculum planted in the field, aphid abundance early in the season, and to a lesser degree temperatures in July and over the preceding winter. Factors correlated with decreased spread included numbers of foliar mineral oil and insecticide sprays (especially of the lambda-cyhalothrin and flonicamid types), later crop planting and earlier first spraying dates. A mid-season leaf test for PVY was shown to be strongly indicative of ultimate PVY spread at harvest, and may prove a useful test in advising growers. A set of locally-relevant best management practices based on these results is discussed.