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Early season aphid activity in 2014
Prolonged exposure to low winter temperatures are known to have lethal and sub-lethal effects on populations of M. persicae which, in Scotland, overwinters in the larval stage. Poor over-winter survival delays the build up of populations of this species in the forthcoming growing season. Prior to 2011, SASA has used the mean temperatures for January and February to predict when M. persicae will become active in the summer. In 2011, following an extremely cold December 2010, SASA predicted early season aphid activity have been based on the mean temperatures during the three-month period of December-February. We intend to continue to use the model based on the three month period.
During winter 2013-14, the mean temperatures were milder than usual: 5.75°C at SASA (Edinburgh; mean = 3.86°C) and 5.1°C at JHI (Dundee; mean = 3.59°C). The winter temperatures for 2013-14 rank the 6th warmest over the past 46 years at Edinburgh and 5th warmest over the past 48 years at Dundee. Based on these figures, the predictions for the first flight of M. persicae is 16 May (average date of first catch is 11 June) at Edinburgh and 28 May (average date of first catch is 16 June) at Dundee. Therefore, M. persicae activity in 2014 is expected to commence 3-4 weeks earlier than in an average summer.
In 2014, the first M. persicae at Edinburgh was recorded on 12 June, one day later than the average date of first catch, and at Dundee on 18 June, two days later than the average date. Despite the relatively warm spring, the predicted early flights failed to materialise.
|2014 Prediction||75% Confidence Limits||2013 Obs'n||
|Myzus persicae||16 May||24 April - 7 June||20 July||12 June|
|Macrosiphum euphorbiae||8 May||17 April - 28 May||5 June||29 April|
|Metopolophium dirhodum||N/A||29 May||28 April|
|Myzus periscae||28 May||2 May - 23 June||7 July||18 June|
|Macrosiphum euphorbiae||13 May||18 April - 8 June||6 May||17 May|
|Metopolophium dirhodum||N/A||28 June||17 May|
The very mild 2013-14 winter indicates that the first flights of M. persicae should be relatively early and therefore have the potential to develop to significant levels. The prediction for the total of M. persicae caught by 31 July is 48 at Dundee and 53 at Edinburgh. The 75% confidence intervals for these predictions are 14 at the lower end and 165 at the upper for Dundee and 14 at the lower end and 192 at the upper for Edinburgh. Therefore, whilst populations of M. persicae may be expected to build up to significant levels during 2014, this risk should be considered in relation to the lowest recorded levels of PLRV inoculum within the Scottish seed crop. Therefore, it is unlikely that there will be a high risk of leafroll transmission in crops of potato varieties other than those that are highly susceptible. However, M. persicae is also a vector of PVY but it appears that only in exceptional year do populations of this species develop within crops to such an extent as to present a risk comparable to that provided by the usually much more numerous cereal aphids.
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