Seed potato growers need to start their insecticide applications earlier and put together more comprehensive programmes to tackle the increasing threat of virus transmission by aphids, Scottish advisor Dr Stuart Wale has warned.

The advice was given at a series of Syngenta potato meetings across Scotland this week.

Wale reported that some of the non-persistent viruses, such as virus A, are appearing earlier in the season.

He said: “We have witnessed an unexpected increase in virus levels, even before aphids conventionally associated with virus spread have been caught in monitoring traps.”

Wale advised 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 changing physiology of virus transmission suggests that growers will need to start programmes as soon as the crop has emerged this season,” he said.

This may mean that growers will have to spray more often over the course of the season, he admitted, but he stressed 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.

Syngenta technical manager Michael Tait highlighted this season’s new potato insecticide, Actara, will give the essential fast aphid knockdown, comparable to the pyrethroids currently used by growers.

Tait reported that 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.

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

Syngenta regional manager Tom Mitchell told Scottish potato growers that fears over options for weed control this season had been allayed with the launch of Retro, a diquat-based contact herbicide that will be a direct replacement for the no longer available PDQ.

Trials have shown Retro can be expected to give the same results enjoyed with PDQ, he said.

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