Twitter has been all of a flutter since the announcement of a derogation for thiamethoxam seed treatment for sugar beet. The newspapers have carried emotive headlines and people have rushed to sign online petitions to ask the government to change its mind. People care about bees.
When it comes to the science that surrounds the neonic debate, the waters have been very murky. With vested interests on both sides, it’s been hard to know what to believe but a substantial body of research seems to be shedding light on what actually happens to these chemicals and their metabolites once treated seed has been planted.
The evidence put forward shows one of the problems with neonics is they’re very persistent in the soil and are highly soluble, so residues can move both downwards and laterally in the soil profile. Those facts suggest that using them in non-flowering crops still poses a risk to invertebrates, countering one of the arguments often put forward to support use in sugar beet.
It’s for these reasons that the derogation has restrictions on following cropping and weed control, designed to mitigate the risk of soil residues being taken up by flowering plants where they may have sub-lethal effects on pollinators.
There are very mixed feelings even within the industry on the return of the neonics, though many sugar beet farmers are understandably relieved that help is at hand should the unprecedented virus threat seen last season be repeated. The handful of insecticides (mostly EAMUs) pressed into filling the hole left after the neonic ban have been woefully inadequate. All the same, it’s surprising the bar to activate the derogation has been set so low, the trigger being a predicted virus forecast of just 9%.
There’s no denying that neonic seed treatments made aphid control very easy – providing a one-stop shop to keep virus levels at a low or non-existent level. They were so good that the industry became completely reliant on just one tool, and very little thought went into looking at alternative methods of control.
Hopes are set on breeding sugar beet varieties with resistance to the yellowing viruses but that shouldn’t mean research should rest on its laurels, comfortable in the knowledge that (this year at least) a neonic may be available to take the strain. This seems to be one of the wider concerns around the derogation.
My bet is that farmers themselves will be the innovators and kick along the research, as seen last season where some growers looked at under-sown barley, released aphid predators into fields and this spring are already looking at companion and intercrop options for the crop.
Agroecological research in the US by John Kempf demonstrates that it’s possible to grow sugar beet crops that are inherently resistant to aphid feeding, with no need to recourse to genetics. By using a complete systems approach – looking at soil chemistry and biology, water quality and SAP analysis of plant tissues – he says it’s possible to manage nutrition in such a way that plants are unattractive to aphids. A further consideration is that seedling health depends on the nutrition received by the mother plant that produced the seed it’s growing from.
In a Zoom meeting well attended by UK growers, he offered to work with them to implement his approach, which is founded on the premise that aphids are only capable of feeding on unhealthy plants. A belief backed up by research from US entomologist, Dr Tom Dykstra, who describes aphids as ‘the lowest of the low’, being equipped to only feed on (unhealthy) plants which have a Brix of below 6. Above that and the sugar levels in the healthier plant will kill aphids because they can’t digest the sugar.
So perhaps it’s time to rethink how we grow sugar beet – from seed production to the farmer’s field – with an emphasis on helping the plant help itself. Current practices put plants under stress from an early stage, before they have much root to sustain them, which coincides with early herbicide application. Is this practice affecting the plant’s attractiveness to aphids? Too much nitrogen affects the constituents of plant sap, providing another reason aphids can syphon off nutrients and in sugar beet, the timing of nitrogen application coincides with peak aphid threat. Is this something that could be looked at?
There’s a real opportunity to embrace some blue-sky thinking when it comes to controlling pests and avoid falling back into a system that relies on just one way of controlling the virus problem. That isn’t a good position to be in.
Based in Ludlow, Shrops, CPM technical editor Lucy de la Pasture has worked as an agronomist. @Lucy_delaP
