Early start for seed potato virus protection

Seed potato growers will need to start their insecticide applications earlier and put together more comprehensive programmes to tackle an increasing threat of virus transmission by aphids, according to leading Scottish advisor, Stuart Wale of SAC.

Speaking at a series of Syngenta Potato meetings across Scotland this week (14 - 18 January), Dr Wale reported that some of the non-persistent viruses - such as Virus A - are appearing earlier in the season. “We have witnessed an

unexpected increase in virus levels, even before aphids conventionally associated with virus spread have been caught in monitoring traps.”

Dr Wale advises that growers will have to revise the practice of waiting for aphid warnings to be issued, or treating when there are signs of them building up in the crop. “The suggestion is that it is non-colonising aphids, such as Cereal Aphids, migrating through the potato crop that are feeding on plants and transmitting the viruses.

“As a result of the rapid action, the reduction in virus levels with Actara is as good as can be currently achieved with pyrethroids”

“The changing physiology of virus transmission suggests that growers will need to start programmes as soon as the crop has emerged this season.” He acknowledges that this may mean growers have to spray more often over the course of the season, but that high grade seed producers have to err on the side of caution - especially on varieties susceptible to virus A such as Russet Burbank and Estima.

“Tolerance of virus infection in Scottish seed is among the lowest in the world, which makes it a key selling point. The incidences we have seen are still extremely low, but do give cause for concern. Growers must act now, to prevent any escalation.”

He believes new insecticide products available in growers’ armoury will allow the more comprehensive approach without creating a risk of resistance developing. Dr Wale advocates that fast aphid knockdown is a key element in

preventing virus transmission, along with the potential of residual activity and repellency to stop aphids landing and feeding on the crop.

Actara gives a new solution for seed producers. Syngenta Technical Manager, Michael Tait, highlighted this season’s new potato insecticide, Actara, will give the essential fast knockdown - comparable to the pyrethroids currently used by growers. “Furthermore, with up to three weeks residual activity and the fact that there is no known resistance makes it a strong base for all seed potato growers’ programmes this season,” he added.

Mr Tait reported trials had shown Actara was faster acting than other new insecticides, such as flonicamid, and could provide a higher level of aphid control, including the most damaging species, Myzus persicae. The long lasting residual activity also provided high levels of control over three weeks after application, when aphid numbers had started to recover on crops treated with other products.

“As a result of the rapid action, the reduction in virus levels with Actara is as good as can be currently achieved with pyrethroids,” he said. “Most importantly, the fast knockdown means that Actara can also reduce transmission of the non-persistent viruses that are rapidly transmitted by feeding aphids.”

Mr Tait added that seed growers are permitted to make a maximum of two applications of Actara in their programmes. He believes the first Actara spray was best placed early in the aphid spray programme to clear out any aphids resistant to other insecticides, and to give protection

through the crucial early growth stages susceptible to virus transmission.

“While Actara is fast acting, some growers may still opt to include Hallmark Zeon in tank mix, to maximize repellency against aphid attack. This strategy will enhance knockdown speed, along with repellency properties that can discourage further aphid activity in the crop,” he advised.

At the end of the season, an application of Actara or Plenum - which also offers a resistance busting option - will kill off resistant aphids that could overwinter and affect next year’s crop; Hallmark Zeon is an essential addition with Plenum when used in seed crops, adds Mr Tait.

Ware crop growers are permitted only one Actara application per season, which is most likely to be used during rapid canopy development when aphid numbers can build rapidly in hot weather.