Aphids and Seed Potatoes

Although our own certified seed production in the UK takes place in areas deemed of low virus risk, seed is currently grown on a wider range of sites than was the case before extension of certified areas.



In addition, there is considerable variation in the risk of virus transmission by aphids between years due to differing aphid population dynamics. This means that whilst there is often a need to spray against aphids, the need should be assessed to prevent unnecessary spraying.



<b>Background</b>



PVY, the cause of severe mosaic virus, is the most important virus of seed potatoes in the UK. A range of symptoms including leaf drop streak and tuber necrosis can be seen and are often specific to certain varieties.



The transmission of PVY, and of PLRV (Potato leaf roll virus) from infected to healthy plants is by aphid feeding and movement. The major culprit is Myzus persicae � the peach potato aphid, although it is not the only species capable of virus transmission.



<b>Control</b>



Prevention of the spread of virus diseases will require knowledge of aphid species present, the level of infection in crops and an understanding of how the population is changing. The effect of aphid predator numbers will also have an affect on spray decisions and choice of product.



<b>Aphid Monitoring</b>



The need to identify the species present and population levels and change is, fortunately, easily met. By placing aphid traps in crops and having their contents assessed on a weekly basis then control decisions are informed by the best possible knowledge of aphid populations.



We have had traps in crops for several years and have despatched them for analysis to DEFRA�s central science laboratory. This year we will be posting the results on our web site and issuing text message spray alerts to participating growers.



<b>Product Choice and Spray Programmes</b>



The subject of pesticide resistance in Myzus persicae populations is a complex one. The implication for spray regimes however is more straightforward.



� Do not rely on a single product or on products from the same chemical group

� Do not use reduced rates of products

� Include at least one application of pymetrozine (Plenum WG)

� Monitor the effectiveness of each spray



In addition, good practice will ensure the following:



� Use predator friendly products wherever possible

� Base spray decisions on crop inspections � not generalised warnings



The following products are approved for aphid control in potato seed and ware crops.



<b>Active Ingredient & Example Product Names</b>



Deltamethrin + Pirimicarb (Evidence)

Lambda � cyhalothrin (Hallmark Zeon)

Lambda � cyhalothrin + pirimicarb (Dovetail)

Pirimicarb (Aphox, Phantom)

Pymetrozine (Plenum WG)



Note � as of this season dimethoate is NOT approved for control of Myzus persicae and its approval on potatoes ceases completely after 30 April 2004.



Always adhere to the full label conditions of product use.



For details of our aphid monitoring programme contact Andy Steven or visit www.higgins.eu.com.