Conditions surrounding the outbreak of yellow dwarf virus in autumn/wintersown cereals in Canterbury during 2005

Abstract

To understand the factors contributing to a severe outbreak of yellow dwarf virus (YDV) in autumn/wintersown wheat in Canterbury in 2005 records of winged cerealinhabiting yellow dwarf virustransmitting aphids caught in the 75 m Lincoln suction trap and the degree day accumulations of ambient temperatures at Lincoln (from 1982 to 2006) were examined as measures of virus infection resulting from primary and secondary aphid infestation respectively The results strongly suggest that infestation by winged aphids into cereal crops was higher than usual throughout winter in 2005 The unusually warm May to August (especially July and August) 2005 enabled a greater than usual aphid buildup (ie through increased development and reproduction) in the crop at this time spreading YDV The unusually high numbers of flying aphids trapped in late spring were the result of additional aphid buildup in cereal crops in September and October The results emphasise the need to include measures of secondary aphid infestation and virus infection in future YDV forecasts