Potato Review

www.potatoreview.com POTATO REVIEW MARCH/APRIL 2022 13 VIRUS / APHIDS POTATO INSECTICIDE RESTRICTIONS – KEY POINTS • Growers advised not to use flonicamid in potatoes until further notice • The advice leaves InSyst as the only systemic product to control colonising aphids • Potato leaf roll virus levels in seed have increased in last two seasons • Lack of chemicals means all IPM methods must be adopted now to stop spread • Use clean input stocks, straw mulch, mineral oil and InSyst as an integrated approach • Consider wildlife strips around/through seed crops to encourage natural predators • Purge strips on headlands can help minimise non-persistent virus spread • Control potato volunteers in surrounding arable fields which are a virus reservoir crop and bare soil, reducing the chances of them landing on plants. In the trials across two sites, 6t/ha of straw was spread across seven beds at a time with a Teagle Tomahawk 8555 Dual Chopper after pre-emergence residual herbicide application and just prior to emergence. The trial scenario was manipulated to be high risk, with infector rows planted in between the plots to increase the chances of virus transmission. Eric says the data showed that straw mulch alone reduced PVY transmission by 40% and PLRV by 59% compared to the untreated plots. With PLRV typically transmitting later, after full crop canopy when straw mulches are less effective, this was a surprise, but Eric believes it may have been as a result of a season when canopies were generally more open. Crop protection The trial also combined the straw mulch with a crop protection programme, which included mineral oil product Crop Spray 11E applied from 30% emergence up to tuber initiation. This was integrated within a programme of four systemic sprays of Tepekki-InSyst- Tepekki-InSyst starting at E50 in response to colonising aphids being caught in yellow water traps as soon as the crop was emerging. A full programme boosted PVY control from 40% to 55% and PLRV control from 59% to 85%, showing the value of using this integrated strategy. “The thing to note is that good levels of control were achieved without pyrethroids, which are wrongly targeted at migratory species like willow-carrot aphid dominant in this trial early- to mid-season. We know they have developed insensitivity to pyrethroids. In this trial, the mineral oil has shown it can mitigate early transmission by cleaning their stylets of virus particles as they feed in the crop,” said Eric. The other practical message from the mulch trial is that wheat straw is more appropriate, as it rotted down better through the season and was readily separated from the crop on the harvester. This year growers will only have the two InSyst systemic sprays and Eric says careful monitoring for colonising aphid activity will be essential to optimise timing. Without AHDB Potatoes funding, growers will no longer have free access to data from FERA’s network of yellow water traps and having one on their farm will cost £500 per trap. Share data However, they must opt in to sharing data, which will enable other subscribers to see their data and vice versa. Scottish Agronomy are actively encouraging seed producers to sign up to improve monitoring on a regional scale. There will also be free access suction trap data as a further decision support tool and Insyst programmes should start as soon as winged colonising aphids like Myzus Persicae are picked up regionally. The final thing to consider is methods to encourage natural predators in and around seed potato crops and it’s been shown that such measures are practical with some careful planning. Eric says wildflower mixtures can be sown in strips not only around the field perimeter, but through the crop on tramlines or between tramline boom tips to ensure the whole crop benefits. These will act as conduits for wildlife and build up aphid predators mid to late season to mitigate colonising aphids. Mixtures should be made up of small, simple flowers like cornflower, common vetch and yarrow and drift reduction nozzles such as Lechler IDTA or Syngenta’s 3D ninety nozzles should be used for late blight and desiccation to ensure strips remain a no spray zone. Eric says his clients have also had success with cereal purge strips, whereby headlands are drilled with spring barley straight after potato planting. “These attract migratory aphids as they initially move into a field and clean their stylet of non-persistent virus in the barley before harmlessly flying onto the seed potatoes. It is clear we no longer have the chemical armoury, so as an industry we must look at integrating all these practices into action to halt the spread of virus,” he said. “It is clear we no longer have the chemical armoury, so as an industry we must look at integrating all these practices into action to halt the spread of virus.” Wildflower strips through potato fields can help encourage natural aphid predators mid to late season, reducing the risk of virus transmission