Aphid action reaps rewards of potato virus reduction

Pete Saunders
Pete Saunders

Potato aphid numbers are now building up, coinciding with many seed crops at early growth stages that are particularly vulnerable to virus infection. The cold, slow start to the growing season for seed crops could see early infection risk increasing.

Seed growers had already been advised to include a pyrethroid insecticide in tank-mix with blight treatments every seven days, reported SRUC specialist, Dr Andy Evans. And with the main vector of potato viruses, Myzus persicae (Peach Potato Aphid) picked up in monitoring across Scotland and the north of England, they should now be looking to include a resistance breaking insecticide in alternate treatments, he advocated.

“A pyrethroid is especially important to manage non-potato colonising migrating aphids that may be carrying viruses and transmitting disease in as little as 30 seconds as they move across a field,” he advised.

Treatment with Hallmark Zeon has also been shown to offer deterrent activity to stop migrating aphids settling or feeding.

Dr Evans highlighted Carrot Willow Aphid and the increasing numbers of Cereal Aphids, for example, that could be spreading infection. “Virus could be picked up from surrounding ware crops, or especially dumps and volunteer potatoes, which we know from studies can frequently be a source of infection,” he warned.

But with Myzus also now present in crops and hedgerows, populations are likely to build up rapidly with any warm dry weather. A rapid increase in numbers in any Myzus colony can quickly trigger the appearance of winged aphids and mass migration.

He cited resistance busting insecticides, such as Actara and Plenum, will be essential tools to include in the programme. They do need to be effectively timed to allow for the restriction of just two neonicotinoid applications, and to utilise Plenum outside of the crop flowering period.

Syngenta Insecticide Technical Manager, Pete Saunders, added that growers can optimise results with Hallmark Zeon, Plenum and Actara from application using angled nozzles, alternating forward and backwards, to enhance crop penetration and coverage of lower leaves. “The target is principally the same as for blight application, so growers will get the best from both elements of the tank mix.

“For earlier applications, until the crop canopy is complete, application in water volume of 100 to 200 l/ha will give good retention on the leaf and optimise sprayer output,” he said. “But where crops get very leafy increasing water volume, up to 400 l/ha, can assure canopy penetration and leaf coverage.”

Dr Andy Evans added that growers and agronomists had made significant advances in reducing virus infection levels in seed crops over recent seasons. He attributed improvements to the combination of implementing the effective new insecticide programmes and better awareness of cultural practices. That has included removal of dumps and volunteer infection sources and intensive roguing of seed crops to remove potentially infected plants.

“There has been a real beneficial reduction in the background reservoir of virus,” he reported. “Potato Leaf Roll Virus (PLRV) is now at very low levels, and whilst non-persistent viruses are still about, such as Potato Virus Y, we have been able to hold them at relatively low levels, compared to several seasons ago.

“It remains vital that growers and agronomists maintain the same attention and efforts for aphid control right through the growing season to burn-down, and even any green regrowth, to prevent any reoccurrence of virus issues,” he added.