Chrysanthemum stem necrosis virus An outbreak of Chrysanthemum stem necrosis virus (CSNV)has been eradicated. The outbreak was in the South West of England and it is most likely that the virus arrived on the nursery in cuttings from Brazil, with the virus then being transmitted from one crop to the next by a local population of western flower thrips (Frankliniella occidentalis).
Due to the isolated nature of the nursery, spread to other sites was considered to be unlikely. As CSNV is an EU IAI listed organism recommendations were given to eradicate CSNV during the period of the outbreak. These included the removal of symptomatic plants and chemical control of the thrips to reduce the vector population. The aim was that there must be 135 days without a finding of CSNV in either plants or thrips before the outbreak could be considered as eradicated. This was considered to be the maximum life span of an individual thrips plus a safety margin.
The last time plants tested positive for CSNV was 11 November 2009. Inspection of the crop and testing of the thrips continued. Thrips taken from traps on 21 January 2010 tested positive for CSNV.
Further samples of thrips were taken in March, April, May and June and all were negative for CSNV. By June, 135 days had passed without a symptomatic plant being identified or a positive test for a plant or a thrips. Therefore the outbreak can be declared eradicated and the status of this pest in the UK is Absent: pest eradicated.