For the first time in a generation, sugar beet growers will have to establish their crops without neonicotinoid seed treatments this season. Dominic Kilburn seeks advice.
The EU’s decision to extend the ban of neonicotinoid seed treatments to all outdoor crops, and not just for flowering types, will have an impact for the first time over the next few weeks as drilling of the 2019 sugar beet crop gets underway.
According to Northants based Indigro and AICC agronomist Damian McAuley, virus yellows has not been an issue for his growers on the basis of neonicotinoid chemistry being ever present as the standard seed treatment to protect crops from the virus, but the ban now leaves growers with precious few options for control.
“Yes, sugar beet farmers coped without those seed treatments in the past, but I would find it hard to tell my growers that if they do nothing about it, their yields could potentially fall this coming season by one third,” he says.
“I’ve seen the data, and the impact of virus yellows on sugar beet can result in a yield loss of between 30–40 per cent, and that’s a real concern,” he adds.
With an emergency authorisation application for the use of neonicotinoid seed treatments (thiamethoxam and clothiadinin) for 2019 refused, chemical options for growers to control virus carrying aphids this season are limited to foliar applied Teppeki (flonicamid).
According to Mr McAuley, Teppeki should be applied only when thresholds have been met (one green wingless aphid per four plants) and up to the 12-leaf stage, after which time plants develop resistance to virus yellows.
“Use of Teppeki is limited to one application per crop, and so, with 21 days’ persistence, timing is everything as we need to get the crop to late May/early June when it can look after itself.”
Growers must engage with the BBRO for advice, and any other forecasting system that predicts when aphids are moving into crops, to help with application timing and make the most of the chemical’s persistence, he stressed.
Mr McAuley rules out the use of pyrethroids for aphid control; a high percentage of the main aphid threat, myzus persicae, has complete resistance to pyrethroid and carbetamide insecticides, while their risk to beneficial insects is too great.
“With every product revocation we get it means that, like much of the agronomy today, cultural control is key,” he says. “It’s about old fashioned farming – a bespoke approach to each field and crop, and attention to detail.”
Lincolnshire-based ProCam agronomist Andrew Mellors agrees that while virus yellows hasn’t been an issue in the relatively recent past, attention to detail going forward will be key in helping to maintain control.
“Where they can, growers need to avoid creating additional green bridges for aphids; beet clamps, dumps and cleanings will all need to be managed to prevent them greening up,” he advises.
He says that it’s critical to get the crop to the 12-leaf stage as soon as possible and that starts with drilling into a “warming” seedbed that is moist, fine and firm.
Trace elements and biostimulants should also be considered from the 4-leaf stage onwards to help reduce stress and the time it takes to get plants to the 12-leaf stage, he adds.
“Importantly, once you get to the threshold for applying Teppeki, then go for it. The product hasn’t got quick knock-down, so if you delay applying it once you get to the threshold, then you risk the virus spreading through the crop. Apply it too early however, and its protection will run out of steam after 21 days, and before the plants are mature enough to resist the virus,” he says.
“Weed control is also a factor,” concludes Mr Mellors. “Herbicides are of course vital in reducing crop competition but growers need to find the right balance between sufficient weed control but without knocking back the crop and checking its growth during establishment.”